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Hydrodynamics and energy analysis of heavy crude oil transportation through horizontal pipelines using novel surfactant
Journal of Petroleum Science and Engineering 178 (2019) 140–151
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Hydrodynamics and energy analysis of heavy crude oil transportation through horizontal pipelines using novel surfactant
T
Manojkumar Gudalaa, Shirsendu Banerjeeb, Tarun Kumar Naiyaa,∗, Ajay Mandala, Subbaiah T.c, Rama Mohan Rao T.d a
Department of Petroleum Engineering, Indian Institute of Technology (ISM), Dhanbad, India School of Chemical Technology, Kalinga Institute of Industrial Technology, Bhubaneswar, India c Department of Chemical Engineering, Vignan's Foundation for Science, Technology & Research (Deemed to be University), Vadlamudi, Guntur, 522213, AP, India d Department of Mechanical Engineering, Vasavi College of Engineering, Hyderabad, India b
ARTICLE INFO
ABSTRACT
Keywords: Heavy crude oil Natural surfactant Pressure drop Shear viscosity pumping power requirement Flow increment
Improvement of flow properties of crude oil through pipelines, the effect of temperature, diameter, water cut, and novel extracted surfactant on pressure drop, shear viscosity was studied along with energy analysis. The impact of diameter, temperature, and the addition of novel surfactant extracted from Madhuca longifolia (Mahua) on pressure drop, shear viscosity, pumping power saving and flow increment were investigated during heavy crude oil flow in horizontal pipelines. Minimum pressure drop was observed in 0.0508 m ID pipeline owing to the collective effect of temperature and 2000 ppm Mahua during the flow of 85% heavy crude oil+15% water. Shear viscosity reduced appreciably in 0.0381 m and 0.0508 m ID pipelines after addition of 2000 ppm Mahua at a temperature of 50 °C. Maximum power saving (130.8%) was achieved and maximum flow increment of 121.8% was accomplished after addition of 2000 ppm Mahua to 85% heavy oil and 15% water mixture during its transportation in 0.0508 m ID pipeline at a 50 °C and at the rate of 7.2 m3/hr. The natural surfactant is substantially efficient to decrease the pumping power consumption for heavy crude oil transportation. It was concluded that the extracted novel natural surfactant is very beneficial for being used as an emulsifier, viscosity reducer, flow improver and also an alternative for the commercial surfactant.
1. Introduction Heavy and extra-heavy crude oil and bitumen occupy a substantial quantity of fossil fuels worldwide. Recent exploration activities estimate that these unconventional oil reserves, which include heavy oils, extra-heavy oils, and bitumen comprise more than 6 × 109 barrels globally (Santos et al., 2014a,b). These heavy crude oils generally have very high viscosity, and their production and transportation using the conventional methods are difficult. Exploration, production, and processing of these crude oils may be subsidiary for the global energy demand and other petroleum derivatives. Heavy crude oils are categorized by high molecular weight with a high content of long chain hydrocarbons, high viscosity, and boiling point. Heavy oils generally comprise four fractions which include saturate, aromatic, resin, and asphaltenes (Ashoori et al., 2017). High density, high viscosity, and little flowability conditions make it difficult to transport heavy and extra heavy crude oil. Therefore, it is vital to reduce the viscosity of heavy and extra heavy crude oil through in-situ operations or
∗
immediate actions after extraction to reduce their costs. During production and transportation of heavy crude oil, their flowability will be significantly changed as their viscosity increases when the temperature decreases and eventually high-pressure drop prevails. Unfortunately, this indefinite issue causes problems during their transportation and even makes production wells blocked (Li et al., 2017). Banerjee et al. (2015)investigated the impact of novel extracted surfactant on pour point, viscosity, interfacial tension and also rheological behavior of Indian heavy crude oil. They concluded that heavy crude oil follows the Power law model. They also concluded that novel extracted surfactant (soapnut) is best suitable to reduce the viscosity, interfacial tension, yield stress, and thixotropic area. In general practice, oil-water emulsion flows in the pipeline is unsteady and irregular (Loh and Premanadhan, 2016). Crude oil-water emulsions have demonstrated positive aspects of energy saving. The issues include cost and power required to produce crude oil-water emulsion and breakage during the processing. The flowing system becomes stable only when using emulsifier or surfactant covers the oil
Corresponding author. E-mail address: [email protected] (T.K. Naiya).
https://doi.org/10.1016/j.petrol.2019.03.027 Received 13 December 2018; Received in revised form 22 February 2019; Accepted 8 March 2019 Available online 14 March 2019 0920-4105/ © 2019 Elsevier B.V. All rights reserved.
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droplets. One of the major concerns is the cost of the surfactant/ emulsifier and the impact of these chemicals on the environment (Loh and Premanadhan, 2016). To solve the complex problems associated with the transportation of heavy crude oil, extensive experimental and theoretical studies have been carried out using both rheological behavior estimation and lab scale flow loop experiments (Gudala et al., 2017; Santos et al., 2017; Zhang et al., 2015; Zhang and Xu, 2016). Rheometers are most frequently employed for the measurement of the viscosity of a fluid. They provide a simple measurement at a high shear rate (Banerjee et al., 2015; Wen et al., 2016). Precise evaluations of rheological behavior, dynamic (shear) viscosity, and pressure drop during transportation of crude oil-water emulsion flow in pipelines are very essential. The understanding of rheological behavior and shear viscosity of fluid/mixtures is required for design, selection, and operation of the equipment involved for mixing, storing, and pumping of oil-water emulsions in pipelines (Wei et al., 2013). Several researchers have studied rheological behavior only using rheometer at different concentrations of water and emulsifier with temperature impact (Banerjee et al., 2015; Loh and Premanadhan, 2016; Sami et al., 2017; Santos et al., 2017; Wen et al., 2016). Zhang et al. (2015) investigated the flow characteristics of heavy crude oil by using rheometer as well as flow loop experiments. They concluded that yield stress and shear stress have a linear relationship when measured by the rheometer and yield stress showed exponential decay with temperature. A good agreement was observed between yield stress and flow rate with experimental data and pipeline flow. Zhang and Xu (2016) studied rheology of synthetic emulsions and their flow properties by using rheometer and laboratory scale flow loop setup. Their investigations revealed that shear-thinning behavior was exhibited near phase inversion region during rheology measurements and phase inversion points were dependent on shear rate. From the flow loop measurements, they found that the phase inversion point was independent of both mixture velocity and pipe diameter at a volume fraction of 0.8 L/L. Savins (1964) concluded that smaller diameter pipelines having more drag reduction because of the action of drag reducer molecules on the boundary layer flow, and the boundary layer takes a larger portion of the total flow in the smaller pipes, subsequent larger pressure drop reductions. Keleşoǧlu et al. (2012) investigated the flowability of water-in-North Sea crude oil in rheometer in addition to flow loop setup. They found that at low temperatures, crude oil, and its emulsions exhibits shear thinning (Power law) behavior. They also found that pressure gradients increase with an increase in the aqueous phase in crude oil emulsions because of the flow rate increments and above 10% of aqueous phase flows were not fully dispersed. Gudala et al. (2017) investigated the impact of naturally extracted surfactant on the rheological behavior of the heavy crude oil and drag reduction analysis. They concluded that crude oil follows the Power law model after adding surfactant at each temperature. They also concluded that drag reduction was substantial after addition of novel surfactant. Heavy crude oils and their emulsions exhibited non-Newtonian behavior, specifically follow Power Law model at all conditions (Gudala et al., 2017; Sami et al., 2017; Santos et al., 2017). Santos et al. (2017) investigated the rheological behavior and frictional energy losses in a 0.75- inch ID horizontal pipeline during the laminar flow of crude oil-water emulsions. They concluded that experimental shear viscosity was three times lower than the original oil viscosity, pressure drop reduced 20 times the value of pure oil flow, inline emulsification was feasible during the pumping and energy required for emulsification is saved. Due to the ability of water and surfactant as a drag reducer, emulsion stability improver and also viscosity reducer, it is beneficial to investigate the shear (flow) viscosity and pressure drop at different flow rates with and without the addition of surfactant and water. This work aims to investigate the pressure drop and shear viscosity of heavy crude oil flow in presence of water and novel extracted surfactant. This work also deals with the comparison of commercial and novel surfactant on pressure drops. Moreover, the impact of Mahua on pumping power
saving and flow increment during the transportation of heavy crude oilwater emulsion was also investigated. 2. Materials and methods 2.1. Materials Heavy crude oil was collected from western regions of India (Mehsana Asset) and used as a test fluid. Ethanol, n-heptane, toluene, sodium sulphate and methanol for extraction of surfactant was procured from Bengal Chemicals, Kolkata, India and Merck Specialities, Mumbai, India. Tergitol 15-S-12, a commercial surfactant was procured from Sigma-Aldrich Chemicals Pvt. Ltd, Banglore, India. Glass microfiber Whatman filter (N934) paper for characterization of crude was purchased from Finar Chemicals, New Delhi, India. 2.2. Characterization of heavy crude oil The density of crude oil determined by using ASTM D891 is 939 kg/ m3 (20 °C), and API gravity was measured using the ASTM D28 method and it was 16.82 at 60 °F. This indicates that the crude used in the study is heavy in nature. ASTM D97-06 method was used to determine the pour point of the heavy crude oil sample and it was 37 °C. Wax content of heavy crude oil was determined by using the BP237 method and is 5.6%. The amount of saturates, asphaltenes, resins and aromatics (SARA) (wt%) contained were measured using SARA analysis and these are 52.23%, 10.48%, 14.23%, and 9.01% respectively. The details of characterization and FTIR spectra were represented in Table 1 and shown in Fig. 1. 2.3. Preparation and characterization of natural surfactant The preparation of surfactant was made using 50 g of Madhuca longifolia fruit shells with a slight modification of the extraction Table 1 Characterization and FTIR spectra of heavy crude oil.
Characterization
FTIR Spectra
Characteristic(s)
Unit
Amount
Exp Method
Saturates Aromatic Resins Asphaltene Pour point Surface tension at 30 °C API Gravity Wax content Water content
Wt % Wt % Wt % Wt % °C mN/m
52.23 9.01 14.23 10.48 37 32.5
SARA SARA SARA SARA ASTM D97-06 Du-nuoy Ring
°API % %
16.82 5.6 5.1
ASTM D28 BP-237 Dean Stark
Wave Number (cm−1)
Functional group
Range (cm−1)
3607
OeH (Monomeric alcohols) OeH (H bonded alcohols, phenols) OeH (H bonded carboxylic acids) OeH (H bonded carboxylic acids) C=H (Aromatic rings) C=O (Aldehydes, ketones, carboxylic acids, esters) C=H (Aromatic rings) NO2 (Nitro compounds) CeO (ethers, carboxylic acids) C=H (Alkenes) (weak)
3590–3650
3419.3 2728.2 2666.7 2417.0 1700.7 1600.0 1306.3 1082.0 723.8
141
3200–3600 2500–2750 2500–2750 2400–2550 1670–1760 1500–1600 1300–1370 1050–1300 675–995
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Fig. 1. FTIR spectra of heavy crude oil.
refluxed for 48 h using reflux condenser. The next step was filtration, followed by distillation of the residue until all the water was collected separately leaving behind mahua oil. Sodium sulphate and ethyl acetate were used to extract the brownish red liquid surfactant from raffinate. The extracted surfactant was passed through anionic and cationic resins to determine the cationic and anionic content respectively. Total organic content was also determined using a carbon sulphur analyzer. Standard methods have been used to characterize the surfactants and results are shown in Table 2. As presented in Table 2, Mahua is basically a non-ionic surfactant with 2.92% cationic content and about 10.67% non-ionic content. It is slightly heavier than water as indicated by the specific gravity with a pronounced specific conductance of 73 microseimens. An FTIR spectrum of natural surfactant is depicted in Fig. 2 to represent the functional groups (Table 2). It was confirmed from FTIR spectra (Fig. 2) that, carboxylic acids and esters were present in the extracted surfactant (Table 2) present in it. Mahua is a natural, biodegradable material which does not have any toxic constituents. Owing to its surfactant properties, it was used for reducing the energy for transporting heavy crude oils via pipelines was done. The research produced encouraging results after the crude oil was beneficiated with mahua. Tests conducted in the laboratory showed that the surfactant has a relatively low boiling point (around 60 °C). There is also a supplementary benefit of it being non-toxic in nature. These properties (especially low boiling point) make it easy to be recovered from the crude oil refineries. Since the surfactant is biodegradable, it won't pose
Table 2 Characterization and FTIR spectra of surfactant extracted from Mahua.
Characterization
FTIR Spectra
Characteristic(s)
Amount
Colour and appearance Specific conductance at 25 °C Specific gravity at 25 °C Total Organic Content (TOC) Non Ionic content Anionic content Cationic content
Brownish red and liquid 73 Microsiemens 1.064 14.32% 10.67% 0.73% 2.92%
Wave Number (cm−1)
Functional group
Range (cm−1)
2157.45 1652.75 1449.23 1379.32 1311.45 1086 721.23
Alkynes Alkenes Alkanes Alkanes Amines Carboxylic acids Alkenes (weak)
2100–2200 1610–1680 1340–1470 1340–1470 1180–1360 1050–1100 675–995
procedures employed by Bhalekar et al. (2017) and Tekin et al. (2016) for extraction of surfactants from soapnut. 50 g of Madhuca longifolia fruits are washed with water and air dried followed by removal of the seeds. The fruits are then vacuum dried to eradicate any moisture left. 300 ml of water was used for refluxing. Skins of Madhuca longifolia were
Fig. 2. FTIR spectra of extracted surfactant Madhuca longifolia (Mahua).
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2.4. Experimental setup for flow behavior study
Table 3 Surface tension of heavy oil and its emulsions at different temperatures. Composition
The experimental test section consisted of two horizontal stainlesssteel pipes (SS304) of 0.0381 m and 0.0508 m ID, both of which were 2.5 m in length, water jacket over the pipes surrounded by insulation to minimize heat loss (Fig. 3). Heavy crude oil and coolant (water) temperatures were adjusted to desired values by controlling bath and chilling circulator temperatures. The percentage of water in the crude oil was varied from 0% to 15% while the temperature was varied from 25 °C to 50 °C. For water-in-oil dispersed flow, water and crude oil were mixed in the oil tank with different proportions of water and oil. The concentration of surfactant was varied from 0 to 2000 ppm in the 15% water and 85% heavy crude oil (V/V), while the temperatures ranged from 25 °C to 50 °C and flow rates were measured using digital flow meters ( ± 5%). Pressure drop was measured using a pressure transducer. The oil-water mixture was circulated through an oil pump into the test pipe to perform pressure drop measurements at different flow rates and temperatures.
Temperature Surface Tension mN/m
Heavy oil 95% Heavy 90% Heavy 85% Heavy 85% Heavy 85% Heavy 85% Heavy 85% Heavy
oil oil oil oil oil oil oil
+ + + + + + +
5% water 10% water 15% water 15% water 15% water 15% water 15% water
+ 500 ppm Mahua + 1000 ppm Mahua +1500 ppm Mahua +2000 ppm Mahua
30 °C
40 °C
50 °C
32.5 32.1 31.6 31.2 30.5 30.1 29.6 29.1
31.8 31.5 31.2 30.9 29.9 29.1 28.3 27.8
30.4 30.1 29.7 29.1 28.5 28.1 27.7 27.1
any harm to the environment or possibly corrode the pipeline. Moreover, a low cost of extraction along with the other aforementioned advantages can make the use of this surfactant beneficial in oil industries. Table 3 presents the surface tension of heavy oil with and without water and Mahua at different temperatures. As evident from the table surface tension decreased with temperature, amount of water and Mahua. Surface tension decreases with increase in temperature due to the reduction of cohesive forces with an increased molecular thermal activity. The heavy oil contains organic acids and salts, alcohols and other natural surface-active agents. When the heavy oil is brought in contact with water, these natural surfactants accumulate at the interface and form an adsorbed film which lowers the surface tension of the heavy oil + water emulsion. Surface tension further decreased after the addition of surfactant. The reduction of surface tension of the heavy oil after addition of water and Mahua may be a contributing factor to reduce the pressure gradient by allowing heavy oil to spread out and allowing more water to flow through the near pipe wall (Robert and Vancko, 1997). It may reduce the wall shear stress and also improve the wall depletion effect. A reduction in the surface tension of the oil, with addition of drag reducing agent (DRA), (i.e., surfactant extracted from Mahua in this case) may be a contributing factor in explaining the mechanism of DRA. A reduction in the surface tension allows the liquid film to spread out, allowing more liquid (crude oil) to flow through the pipe. This spreading out of the liquid film resembles annular flow.
3. Results and discussions 3.1. Experimental pressure drop analysis during heavy crude oil flow The impact of diameter and temperature along with novel surfactant on pressure drop and shear viscosity was investigated. Pressure drop was measured by using the pressure transducers at both ends of the test section and the flow rate was measured by using flow meter (Fig. 3). 3.1.1. Effect of temperature and diameter on pressure drop Temperature was the most dominant factor during the pipeline transportation of heavy crude oil. Fig. 4 depicts the effect of temperature on the pressure drop during the transport of heavy crude oil in 0.0381 m and 0.0508 m ID pipelines. It was observed from the experimental results that pressure drops reduced appreciably in both the pipelines with an increase in temperature. As the temperature of the test fluid increases, the viscosity of the heavy crude oil/emulsions decreases which reduces the shear stress between flowing fluid and pipe wall and ultimately improve transportability (Martínez-Palou et al., 2011; Hart, 2014). The impact of flow rate along with temperature was also investigated as shown in the figure. Correspondingly, pressure drop reduced from 0.042 MPa/m to 0.0198 MPa/m (52.85%) and 0.034 MPa/
Fig. 3. Experimental setup pipeline for heavy oil flow.
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is that surfactant can also make a coating over the paraffin and inhibit them to coalesce which may significantly decrease the turbulent frictional factor (Wang et al., 2016). Moreover, wall slip effect is also a very significant contributing factor (Yoshimura and Prudhomme, 1988; Barnes, 1995). It can be concluded that Mahua is partly modifying the pipe wall surface. Thus, Mahua may control the excessive generation and growth of turbulent flow and reduce the pressure drop in all pipelines. Fig. 6 shows the comparison of two surfactants, the surfactant extracted from Madhuca longifolia and a commercial surfactant Tergitol on pressure drop via 0.0381 m ID and 0.0508 m ID pipelines. As evident in Fig. 6, the results are comparable. However, as the novel surfactant is easy to synthesize and easily available, it has an edge over the commercially used surfactant. Table 4 presents a comparison of the data obtained. Natural surfactant Mahua can replace the commercial surfactants to improve the flowability of heavy oils. 3.1.3. Development of friction factor correlations The Fanning friction factor is given by (Guo et al., 2018)
ff =
Fig. 4. Effect of diameter and temperature on the pressure drop during the flow of heavy oil.
2L
D p 2 mix Uavg
(1)
where, D is the diameter of the pipe (m), p is the pressure drop (Pa), L is the length of the pipeline (m), Uavg is the average velocity of the fluid (m/s), and mix is the density of the mixture (kg/m3). Reynolds number and mix are defined as
m to 0.0196 MPa/m (42.35%) when temperature increased from 25 °C to 50 °C during flow of the oil via 0.0381 m ID and 0.0508 m ID pipelines respectively at flow rates of 2.4 m3/h and 3.6 m3/h. The reason for this is suggested due to the reduction of heavy oil viscosity with temperature which reduces the shear stress between the heavy oil and pipe wall during transportation (Hart, 2014). Therefore, heating improves the transportability of heavy oil via pipelines by reducing the viscosity and consequently shear stress at the pipe wall (Saniere et al., 2004; Hart, 2014; Martínez-Palou et al., 2011). It was seen that pressure drop reduced with an increase in diameter at a constant flow rate and temperature. It reduced from 0.0354 MPa/m to 0.026 MPa/m (26.34%) when the inner diameter of the pipeline changed from 0.0381 m ID to 0.0508 m ID at a flow rate of 1.2 m3/hr and 25 °C. As the cross-sectional area of the pipeline decreases (i.e., at constant length) the velocity of the fluid in the narrower pipeline increases in order to maintain constant flow rate (i.e., Bernoulli's equation). This increased fluid velocity reduces the static pressure (Çengel and Cimbala, 2013). Similarly, if the inner diameter of the pipeline increases, the velocity of the fluid decreases to maintain a constant flow rate, which increases the static pressure. Therefore, the pressure drop decreases with an increase in the inner diameter (ID) of the pipeline at a constant flow rate and temperature (i.e., from 0.0381 m ID to 0.0508 m ID).
Rem =
mix
=
DUavg
mix
(2)
µshear o
+ (1
)
w
(3)
where, µshear is the shear viscosity (Pa.s), o and w are the densities of oil and water (kg/m3), and is the volume phase fraction of oil (%). The relation between friction factor and Reynolds number is shown in Fig. 7 (A-C) by using equations (1) and (2). It was observed that friction factor reduced with the amount of dispersed water and addition of natural surfactant in each temperature which is an analogous representation to the pressure drop. It was also seen that all the friction factors are in-line with the Reynolds number. Correlations were developed by using linear regression analysis for heavy crude oil flows without and with water and natural surfactant and shown in equations (4)–(6) respectively [Fig. 7(A-C)].
3.1.2. Impact of diameter and surfactant on pressure drop The impact of surfactant addition on pressure drop at different temperatures in both the pipelines is depicted in Fig. 5 for only crude oil flow in each pipeline. The addition of novel surfactant in water reduced the pressure drops effectively during the flow of crude oil in each pipeline. It was also observed that the minimum pressure drops were obtained after addition of 2000 ppm of Mahua to 85% heavy crude oil +15% water. Pressure drop reduction of 55.18% (0.027 MPa/m to 0.0121 MPa/m), and 76.12% (0.0272 MPa/m to 0.0065 MPa/m) was achieved in 0.0381 m (6.6 m3/hr) and 0.0508 m ID (7.2 m3/hr) pipelines respectively after addition of 15% water and 2000 ppm Mahua to heavy oil. High pressure drops occur during the flow of crude oil at low temperatures. High-pressure drop in a pipeline is unfavorable from the industrial point of view due to high pumping power requirement. The addition of Mahua may improve the pressure drop reduction by the forming rod-shaped micelles with shear degradation resistance performance. These rod-shaped micelles can absorb the excess energy of the turbulent flow (i.e., the generated shear stresses at the pipe wall surface) (Wang et al., 2016). The other reason for pressure drop reduction
f f ,0.0381m =
31.71 Re1.076 m
(4)
f f ,0.0508m =
28.4 Re1.114 m
5)
f f , all pipe =
24.2 0.9945 Rem
(6)
These correlations show that friction factors are diameter dependent. The friction factor generally decreases with the increase in the Reynolds number, especially at high concentrations of water and surfactants. Fig. 7 (A1-C1) depicts the percentage deviation of the experimental predicted values from equations (4)–(6). The results show that equations (4) and (5) depict deviation of ± 10% and equation (6) shows ± 20%. 3.1.4. Uncertainty in measurement The uncertainty in measurements was carried out on the pressure drop measurements. Quantitative measurements on pressure drop during the heavy oil transportation at different flow rate tend to be normally distributed. The SD (Standard Deviation) and SE (Standard Error) were determined using equations (7) and (8) respectively 144
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Fig. 5. Effect of Mahua on pressure drop during flow of heavy oil at 30 °C.
Fig. 6. Comparison of natural (Mahua) and commercial (Tergitol) surfactants on pressure drop in two pipelines to 85% HO + 15% W at 35 °C.
Table 4 Comparison of natural and commercial surfactant on pressure drops during the flow of 85% Heavy crude oil +15% Water at 5 m3/hr at 35 °C. Sl. No
Concentration, ppm
(Pressure gradient), MPa/m 0.0381 m-ID pipeline
1 2 3 3
500 1000 1500 2000
0.0508 m-ID pipeline
Mahua
Tergitol
Variation%
Mahua
Tergitol
Variation%
0.0251 0.0215 0.0207 0.0181
0.0242 0.0222 0.0197 0.0191
3.58 3.25 4.83 5.52
0.0169 0.0149 0.0132 0.0116
0.0176 0.0147 0.0133 0.0119
4.14 1.348 0.75 2.58
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Fig. 7. Correlation development for friction factor using Reynolds number (A–C) Percentage deviation of the experimental and friction factor equations (A1-C1).
Fig. 8. Uncertainty analysis (standard error) of pressure drop measurements.
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additive concentrations (Keleşoǧlu et al., 2012). The consistency index (K) shows the opposite change to the flow behavior index (n) (Fig. 9). The decrease in consistency index (K) and an increase in the flow behavior index (n) were achieved with an increase in temperature, water cut, and additives concentration (Fig. 9). The flow behavior index (n) represents the degree of non-Newtonian characteristic of the heavy oil/ emulsions. This decrease in consistency index (K) and an increase in flow behavior index (n) represents the decrease in the viscosity of the heavy oil/emulsions. Significant improvements in rheological behavior near the pipe wall have been observed after addition of Mahua (Fig. 9). The additive Mahua effectively reduced the consistency index (K) and increased the flow behavior index (n) during the flow of 85% heavy oil15% water via pipelines. After addition of Mahua to the heavy oil-water emulsions flow behavior index values tend towards unity (i.e., Newtonian behavior). This shows that the fluid changes its operational rheological behavior towards Newtonian behavior from shear thinning behavior with an increase in temperature, the volume of water, and the concentration of additive.
Table 5 Parameters of uncertainty analysis. Parameter
Value
Mean Standard Error Standard Deviation Sample Variance Kurtosis Minimum Maximum Confidence Level (95.0%)
2.042E-02 2.574E-04 7.563E-03 5.719E-05 −4.768E-01 3.585E-03 4.109E-02 5.053E-04
n i=1
SD
p
=
SE
p
=
SD
¯p L
pi L n
(7)
p
(8)
n
3.2.2. Effect of Mahua on shear viscosity Fig. 10 presents the effect of the Mahua on shear viscosity during the flow of 85% heavy oil +15% water in 0.0381 m ID, and 0.0508 m ID pipelines. As seen in Fig. 10 shear viscosity reduced after addition of Mahua in all the pipelines. It was also observed that the in-situ rheological behavior of 85% heavy oil+ 15% water tends to move towards Newtonian from the shear thinning behavior (n = 0.2181 to 0.9834) after addition of 2000 ppm Mahua at 50 °C. Viscosity reduction capacity of Mahua in comparison to other surfactants and solvents reported in the literature is shown in Table 6. Viscosity reduction data obtained with the surfactant is comparable with those from literature. Due to paraffin dissolution and diminishing of the excessive energy (i.e., for generated shear stresses at pipe wall surface) capabilities of Mahua, and with promotion of wall depletion effect can reduce the shear viscosity in all pipelines. Therefore, the addition of Mahua improves the operational rheological behavior during the transportation of 85% heavy oil +15% water in pipelines effectively.
th
where n is the sample size, pi is the pressure drop of i measurement, and p is the mean pressure drop from measurements. Fig. 8 depicts the standard error for the pressure drop measurement. The standard deviation of 7.563 × 10−3 and standard error of 2.57 × 10−4 was seen for the pressure drop measurements from the experimental setup (Table 5). This means that the investigations of pressure drop produced very low errors. 3.2. Studies on shear viscosity during pipeline flow of heavy crude oil/ emulsion During the of heavy oil transportation in pipelines, shear (i.e., operational) rate, shear viscosities, and flow behavior index were calculated using pressure drop and flow rates equations described by the Gudala et al. (2018).
n=
wall
a
=
d log( w ) d log( a )
(9)
p x
(10)
=
D 4
4Q D3
µshear = K
3.3. Effect of water cut, and mahua on flow development The mechanism of flow development using hydrodynamic entry length is explained in previous works. The distance from the entry to the maximum velocity (disappearing point of boundary layer) location is called the hydrodynamic entry/entrance length (Gudala et al., 2018). During transportation of fluid in horizontal pipes, hydrodynamic entry length depends not only on the Reynolds number but also on water cut and surfactant concentration. In this research hydrodynamic entry length was investigated at different flow rates, temperature, water cut and surfactant concentrations in the heavy crude oil. The hydrodynamic entrance length is calculated by using a correlation given by Durst et al. (2005) in equation (13). Correlation with exponents for a wide range of Reynolds number (0 < Rem < ) was developed by Durst et al. (2005) using numerical investigations which showed an error of 3% under suggestions of Churchill and Usagi (1972) where asymptotic behavior of hydrodynamic entry lengths was considered.
(11)
3n + 1 4n
n 1
32Q D3
n 1
(12)
where w wall shear stress (Pa), a is apparent wall shear rate (s−1), K is consistency index (Pa.sn), n is flow behavior index, Q is flow rate (m3/hr). 3.2.1. Effect of temperature, water cut and additives on consistency index (K) and flow behavior index (n) Viscosity is one of the crucial parameters of a fluid to be transported via pipelines. During the transportation of heavy crude oil (i.e., operational) shear rate (equation (11)) and shear viscosities (equation (12)) were calculated from the pressure drop and flow rate. For a real fluid, many flow models are present in the literature which relate viscosity with the shear stress (equation (10)) and shear rate. Fig. 9 presents the Power law model constants during the transportation of heavy oil after adding water and additives at a different temperature. To suggest whether a fluid is Newtonian or non-Newtonian, sometimes consistency index (k) and flow behavior index (n) is employed. A fluid is likely to show Newtonian characteristics if its flow behavior index is close to unity and consistency index has high values, and vice versa. The consistency index (K) (equation (12)) and flow behavior index (n) (equation (9)) are dependent on the temperature, water cut and
Lh = [0.6191.6 + (0.0567 Rem)1.6 ]1/1.6
(13)
Equation (13) is valid in the range of 0 < Rem < . At constant flow rate and diameter, Reynolds number was dependent on the density and shear viscosity of the heavy oil and its emulsions. It was seen that hydrodynamic entrance lengths (i.e., flow developing length) increased with the temperature of the flowing fluid at a constant flow rate (Fig. 11). It is due to variation in shear viscosity of the heavy oil with temperature. The hydrodynamic entrance lengths increased gradually with increasing water cut in the heavy oil at a constant flow rate. This may be due to the increasing wall depletion effect during crude oil flow after the addition of water in both the pipelines. It reduces the shear 147
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Fig. 9. Consistency index (K) and flow behavior index (n) of the heavy oil (HO) during the transportation in 0.0381 m ID and 0.0508 m ID pipelines at different temperatures, water cut (W) and Mahua concentration.
Fig. 10. Effect of mahua on shear viscosity during heavy oil flow through 0.0381 m ID and 0.0508 m ID pipelines at 45 °C. 148
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Table 6 Comparison of viscosity reduction capacity of Mahua with different solvents and surfactants. Sl. No I 1 2 3 4 5 6 7 8 9 10 II 11 12 13 14 15 16 17 18 19 20 21 22 23
Additive Solvent addition Xylene Xylene Toluene Benzene Emulsion Emulsion Light oil PRCW E1 Light crude oil Light Oil Surfactant addition EVA-80 EVA-80 EVA-80 EVA 32 EVA 32 EVA 32 EVA 32 EVA 32 E1T6 E3T6 Copolymer of ethylene and vinyl acetate 15% water and Mahua 15% water and Mahua
Amount of additive added
% viscosity reduction
Temperature, °C
Reference
5% v/v 3% v/v 5% v/v 5% v/v 10% v/v 20% v/v 10% v/v 5% v/v 30% v/v 50% v/v
27 22 26 24 11.5 49 87 77.9 98% 55%
40 40 40 40 45 45 45
Taraneh et al. (2008)
50 40
2000 ppm 2000 ppm 2000 ppm 2000 ppm 2000 ppm 2000 ppm 2000 ppm 2000 ppm 1000 ppm 1000 ppm 1000 ppm 2000 ppm 2000 ppm
88 78 58 64 85 52 28 29 17.69 12.05 22.1 48.9 57.5
20 15 10 40 20 15 10 5 40 40 40 45 45
Hasan et al. (2010) Etoumi (2007) Yaghi and Al-Bemani (2002) Ashrafizadeh and Kamran (2010) Taraneh et al. (2008)
Hafiz and Khidr (2007) Pedersen and Rønningsen (2003) This work (at 200 s−1 in 0.0381 m ID pipeline) This work (at 100 s−1in 0.0508 m ID pipeline)
for the fluid to obtain improved flow behavior.
viscosity and increases the hydrodynamic entrance length (Lh). It was also seen that Mahua has a significant effect on the hydrodynamic entrance lengths. It is due to the promotion of wall depletion effect after the addition of Mahua to the 85% heavy oil +15% water during the flow. The maximum hydrodynamic length was observed at 50 °C and 2000 ppm of mahua to the 85% heavy oil + 15% water during transportation in each pipeline (Fig. 11). This increase in hydrodynamic entrance length shows that the boundary layer develops slowly after addition of the water and mahua to the heavy oil at a constant flow rate and temperature. Therefore, the addition of water and mahua to the heavy oil slow down the boundary layer development by reducing the shear viscosity (i.e., hydrodynamic entrance length increase). As a result, the hydrodynamic entrance length will increase giving more time
3.4. Pumping power requirements for the flow of crude oil Instead of using a greater number of pumps and/or looping, surfactant addition is a preferable choice to increase transportation efficiency. Investigation of the pumping power of the system was done to explore this fact. Saving in pumping power was investigated in terms of head loss before and after addition of Mahua at different flow rates. The percentage of drag reduction in terms of friction factor was defined as
%DR = 1
fMahua f
× 100
Fig. 11. Effect of temperature, water cut, and Mahua on the hydrodynamic entrance length (Lh) during the flow of heavy oil via pipelines at flow rates. 149
(14)
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Fig. 12. Pumping power saving during the transportation of Heavy oil after the addition of water and Mahua at different flow rates and temperatures.
where, fMahua is friction factor after addition of Mahua and %DR is the drag reduction percentage. Head loss is calculated by simultaneous consideration of drag reduction (equation (14)) and Darcy-Weisbach equation. The relation between head loss before and after addition of Mahua was defined as
hL
Mahua
%DR × hL 100
= 1
diameter after addition of water and Mahua during the flow of heavy oil. Maximum pressure drops were achieved in 0.0381 m ID pipeline (at 25 °C) and minimum pressures drop occur in 0.0508 m ID pipeline during the flow of 85% heavy oil + 15% water after addition of 2000 ppm of Mahua at 50 °C. Mahua shows better pressure drop reduction capabilities due to its encouraging abilities such as modifying the pipe wall surface, control of excessive generation and growth of turbulence via pipelines. Correlations were developed by using the linear regression analysis to predict the friction factors with and without water and bio-additive for heavy oil transportation. The developed correlations show good agreement with the experimental results (i.e., deviation ± 10% and ± 20%). Minimum shear viscosity was detected in 0.0381 m ID and maximum occurs in 0.0508 m ID pipeline during the transportation of heavy oil at 50 °C and 25 °C respectively. Maximum flow behavior index of 0.9843 was seen after addition of 2000 ppm Mahua to the crude oil at 50 °C via 0.0508 m ID pipeline. Mahua showed excellent capabilities to improve the pumping power requirement saving and flow increments. The extracted novel natural surfactant is highly beneficial for being used as an emulsifier, pressure drop reducer, flow improver and decreasing the pumping power consumption.
(15)
where, hL is the head loss (m). The extracted surfactant reduced the friction and consequently the pumping requirement of this crude oil changed. The saving in pumping power requirements overcomes the head loss as a result of added surfactant at each flow rate and temperature can be expressed as follows (Al-Wahaibi et al., 2017)
Wps =
g (hL
hL
Mahua)
× QT
(16)
where Wsp is the saving in power required (%) and QT is the total volumetric flow rate (m3/hr). Fig. 12 depicts the percentage savings in the pumping power requirements during flow as a function of surfactant concentration with a flow rate ranging from 2.4 to 6.6 m3/hr (i.e., for 0.0381 m ID), 3-7.2 m3/hr (i.e., for 0.0508 m ID) and temperature ranging from 25 °C-50 °C. It can be seen that after the addition of Mahua to 85% heavy crude oil + 15% water, the amount of power saved increased progressively in all pipelines. Power saving was achieved to about 128.7% (6.6 m3/hr) and 130.8% (7.2 m3/hr) during the 85% heavy oil + 15% water transportation at 50 °C after addition of 2000 ppm Mahua in 0.0381 m, and 0.0508 m ID pipelines respectively. Results also show that the percentage of power saved increased with an increase in flow rate and temperature in all pipelines and decreased with an increase in inner diameter of the pipeline (Al-Wahaibi et al., 2017). This increasing pumping power saving is due to the fact that flow rate would increase the turbulence intensity which enhances the performance of Mahua by increasing the drag reduction, wall depletion effect (Al-Wahaibi et al., 2017; Santos et al., 2014a,b).
Acknowledgment IIT (ISM), Dhanbad, India, [FRS (42)/2012–2013/PE] and DST (SERB), India [Project no:EEQ/2016/00650], The authors would also like to thank ONGC Ltd, India for supplying the heavy crude oil. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.petrol.2019.03.027. References
4. Conclusions
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Hydrodynamics and energy analysis of heavy crude oil transportation through horizontal pipelines using novel surfactant
T
Manojkumar Gudalaa, Shirsendu Banerjeeb, Tarun Kumar Naiyaa,∗, Ajay Mandala, Subbaiah T.c, Rama Mohan Rao T.d a
Department of Petroleum Engineering, Indian Institute of Technology (ISM), Dhanbad, India School of Chemical Technology, Kalinga Institute of Industrial Technology, Bhubaneswar, India c Department of Chemical Engineering, Vignan's Foundation for Science, Technology & Research (Deemed to be University), Vadlamudi, Guntur, 522213, AP, India d Department of Mechanical Engineering, Vasavi College of Engineering, Hyderabad, India b
ARTICLE INFO
ABSTRACT
Keywords: Heavy crude oil Natural surfactant Pressure drop Shear viscosity pumping power requirement Flow increment
Improvement of flow properties of crude oil through pipelines, the effect of temperature, diameter, water cut, and novel extracted surfactant on pressure drop, shear viscosity was studied along with energy analysis. The impact of diameter, temperature, and the addition of novel surfactant extracted from Madhuca longifolia (Mahua) on pressure drop, shear viscosity, pumping power saving and flow increment were investigated during heavy crude oil flow in horizontal pipelines. Minimum pressure drop was observed in 0.0508 m ID pipeline owing to the collective effect of temperature and 2000 ppm Mahua during the flow of 85% heavy crude oil+15% water. Shear viscosity reduced appreciably in 0.0381 m and 0.0508 m ID pipelines after addition of 2000 ppm Mahua at a temperature of 50 °C. Maximum power saving (130.8%) was achieved and maximum flow increment of 121.8% was accomplished after addition of 2000 ppm Mahua to 85% heavy oil and 15% water mixture during its transportation in 0.0508 m ID pipeline at a 50 °C and at the rate of 7.2 m3/hr. The natural surfactant is substantially efficient to decrease the pumping power consumption for heavy crude oil transportation. It was concluded that the extracted novel natural surfactant is very beneficial for being used as an emulsifier, viscosity reducer, flow improver and also an alternative for the commercial surfactant.
1. Introduction Heavy and extra-heavy crude oil and bitumen occupy a substantial quantity of fossil fuels worldwide. Recent exploration activities estimate that these unconventional oil reserves, which include heavy oils, extra-heavy oils, and bitumen comprise more than 6 × 109 barrels globally (Santos et al., 2014a,b). These heavy crude oils generally have very high viscosity, and their production and transportation using the conventional methods are difficult. Exploration, production, and processing of these crude oils may be subsidiary for the global energy demand and other petroleum derivatives. Heavy crude oils are categorized by high molecular weight with a high content of long chain hydrocarbons, high viscosity, and boiling point. Heavy oils generally comprise four fractions which include saturate, aromatic, resin, and asphaltenes (Ashoori et al., 2017). High density, high viscosity, and little flowability conditions make it difficult to transport heavy and extra heavy crude oil. Therefore, it is vital to reduce the viscosity of heavy and extra heavy crude oil through in-situ operations or
∗
immediate actions after extraction to reduce their costs. During production and transportation of heavy crude oil, their flowability will be significantly changed as their viscosity increases when the temperature decreases and eventually high-pressure drop prevails. Unfortunately, this indefinite issue causes problems during their transportation and even makes production wells blocked (Li et al., 2017). Banerjee et al. (2015)investigated the impact of novel extracted surfactant on pour point, viscosity, interfacial tension and also rheological behavior of Indian heavy crude oil. They concluded that heavy crude oil follows the Power law model. They also concluded that novel extracted surfactant (soapnut) is best suitable to reduce the viscosity, interfacial tension, yield stress, and thixotropic area. In general practice, oil-water emulsion flows in the pipeline is unsteady and irregular (Loh and Premanadhan, 2016). Crude oil-water emulsions have demonstrated positive aspects of energy saving. The issues include cost and power required to produce crude oil-water emulsion and breakage during the processing. The flowing system becomes stable only when using emulsifier or surfactant covers the oil
Corresponding author. E-mail address: [email protected] (T.K. Naiya).
https://doi.org/10.1016/j.petrol.2019.03.027 Received 13 December 2018; Received in revised form 22 February 2019; Accepted 8 March 2019 Available online 14 March 2019 0920-4105/ © 2019 Elsevier B.V. All rights reserved.
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droplets. One of the major concerns is the cost of the surfactant/ emulsifier and the impact of these chemicals on the environment (Loh and Premanadhan, 2016). To solve the complex problems associated with the transportation of heavy crude oil, extensive experimental and theoretical studies have been carried out using both rheological behavior estimation and lab scale flow loop experiments (Gudala et al., 2017; Santos et al., 2017; Zhang et al., 2015; Zhang and Xu, 2016). Rheometers are most frequently employed for the measurement of the viscosity of a fluid. They provide a simple measurement at a high shear rate (Banerjee et al., 2015; Wen et al., 2016). Precise evaluations of rheological behavior, dynamic (shear) viscosity, and pressure drop during transportation of crude oil-water emulsion flow in pipelines are very essential. The understanding of rheological behavior and shear viscosity of fluid/mixtures is required for design, selection, and operation of the equipment involved for mixing, storing, and pumping of oil-water emulsions in pipelines (Wei et al., 2013). Several researchers have studied rheological behavior only using rheometer at different concentrations of water and emulsifier with temperature impact (Banerjee et al., 2015; Loh and Premanadhan, 2016; Sami et al., 2017; Santos et al., 2017; Wen et al., 2016). Zhang et al. (2015) investigated the flow characteristics of heavy crude oil by using rheometer as well as flow loop experiments. They concluded that yield stress and shear stress have a linear relationship when measured by the rheometer and yield stress showed exponential decay with temperature. A good agreement was observed between yield stress and flow rate with experimental data and pipeline flow. Zhang and Xu (2016) studied rheology of synthetic emulsions and their flow properties by using rheometer and laboratory scale flow loop setup. Their investigations revealed that shear-thinning behavior was exhibited near phase inversion region during rheology measurements and phase inversion points were dependent on shear rate. From the flow loop measurements, they found that the phase inversion point was independent of both mixture velocity and pipe diameter at a volume fraction of 0.8 L/L. Savins (1964) concluded that smaller diameter pipelines having more drag reduction because of the action of drag reducer molecules on the boundary layer flow, and the boundary layer takes a larger portion of the total flow in the smaller pipes, subsequent larger pressure drop reductions. Keleşoǧlu et al. (2012) investigated the flowability of water-in-North Sea crude oil in rheometer in addition to flow loop setup. They found that at low temperatures, crude oil, and its emulsions exhibits shear thinning (Power law) behavior. They also found that pressure gradients increase with an increase in the aqueous phase in crude oil emulsions because of the flow rate increments and above 10% of aqueous phase flows were not fully dispersed. Gudala et al. (2017) investigated the impact of naturally extracted surfactant on the rheological behavior of the heavy crude oil and drag reduction analysis. They concluded that crude oil follows the Power law model after adding surfactant at each temperature. They also concluded that drag reduction was substantial after addition of novel surfactant. Heavy crude oils and their emulsions exhibited non-Newtonian behavior, specifically follow Power Law model at all conditions (Gudala et al., 2017; Sami et al., 2017; Santos et al., 2017). Santos et al. (2017) investigated the rheological behavior and frictional energy losses in a 0.75- inch ID horizontal pipeline during the laminar flow of crude oil-water emulsions. They concluded that experimental shear viscosity was three times lower than the original oil viscosity, pressure drop reduced 20 times the value of pure oil flow, inline emulsification was feasible during the pumping and energy required for emulsification is saved. Due to the ability of water and surfactant as a drag reducer, emulsion stability improver and also viscosity reducer, it is beneficial to investigate the shear (flow) viscosity and pressure drop at different flow rates with and without the addition of surfactant and water. This work aims to investigate the pressure drop and shear viscosity of heavy crude oil flow in presence of water and novel extracted surfactant. This work also deals with the comparison of commercial and novel surfactant on pressure drops. Moreover, the impact of Mahua on pumping power
saving and flow increment during the transportation of heavy crude oilwater emulsion was also investigated. 2. Materials and methods 2.1. Materials Heavy crude oil was collected from western regions of India (Mehsana Asset) and used as a test fluid. Ethanol, n-heptane, toluene, sodium sulphate and methanol for extraction of surfactant was procured from Bengal Chemicals, Kolkata, India and Merck Specialities, Mumbai, India. Tergitol 15-S-12, a commercial surfactant was procured from Sigma-Aldrich Chemicals Pvt. Ltd, Banglore, India. Glass microfiber Whatman filter (N934) paper for characterization of crude was purchased from Finar Chemicals, New Delhi, India. 2.2. Characterization of heavy crude oil The density of crude oil determined by using ASTM D891 is 939 kg/ m3 (20 °C), and API gravity was measured using the ASTM D28 method and it was 16.82 at 60 °F. This indicates that the crude used in the study is heavy in nature. ASTM D97-06 method was used to determine the pour point of the heavy crude oil sample and it was 37 °C. Wax content of heavy crude oil was determined by using the BP237 method and is 5.6%. The amount of saturates, asphaltenes, resins and aromatics (SARA) (wt%) contained were measured using SARA analysis and these are 52.23%, 10.48%, 14.23%, and 9.01% respectively. The details of characterization and FTIR spectra were represented in Table 1 and shown in Fig. 1. 2.3. Preparation and characterization of natural surfactant The preparation of surfactant was made using 50 g of Madhuca longifolia fruit shells with a slight modification of the extraction Table 1 Characterization and FTIR spectra of heavy crude oil.
Characterization
FTIR Spectra
Characteristic(s)
Unit
Amount
Exp Method
Saturates Aromatic Resins Asphaltene Pour point Surface tension at 30 °C API Gravity Wax content Water content
Wt % Wt % Wt % Wt % °C mN/m
52.23 9.01 14.23 10.48 37 32.5
SARA SARA SARA SARA ASTM D97-06 Du-nuoy Ring
°API % %
16.82 5.6 5.1
ASTM D28 BP-237 Dean Stark
Wave Number (cm−1)
Functional group
Range (cm−1)
3607
OeH (Monomeric alcohols) OeH (H bonded alcohols, phenols) OeH (H bonded carboxylic acids) OeH (H bonded carboxylic acids) C=H (Aromatic rings) C=O (Aldehydes, ketones, carboxylic acids, esters) C=H (Aromatic rings) NO2 (Nitro compounds) CeO (ethers, carboxylic acids) C=H (Alkenes) (weak)
3590–3650
3419.3 2728.2 2666.7 2417.0 1700.7 1600.0 1306.3 1082.0 723.8
141
3200–3600 2500–2750 2500–2750 2400–2550 1670–1760 1500–1600 1300–1370 1050–1300 675–995
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Fig. 1. FTIR spectra of heavy crude oil.
refluxed for 48 h using reflux condenser. The next step was filtration, followed by distillation of the residue until all the water was collected separately leaving behind mahua oil. Sodium sulphate and ethyl acetate were used to extract the brownish red liquid surfactant from raffinate. The extracted surfactant was passed through anionic and cationic resins to determine the cationic and anionic content respectively. Total organic content was also determined using a carbon sulphur analyzer. Standard methods have been used to characterize the surfactants and results are shown in Table 2. As presented in Table 2, Mahua is basically a non-ionic surfactant with 2.92% cationic content and about 10.67% non-ionic content. It is slightly heavier than water as indicated by the specific gravity with a pronounced specific conductance of 73 microseimens. An FTIR spectrum of natural surfactant is depicted in Fig. 2 to represent the functional groups (Table 2). It was confirmed from FTIR spectra (Fig. 2) that, carboxylic acids and esters were present in the extracted surfactant (Table 2) present in it. Mahua is a natural, biodegradable material which does not have any toxic constituents. Owing to its surfactant properties, it was used for reducing the energy for transporting heavy crude oils via pipelines was done. The research produced encouraging results after the crude oil was beneficiated with mahua. Tests conducted in the laboratory showed that the surfactant has a relatively low boiling point (around 60 °C). There is also a supplementary benefit of it being non-toxic in nature. These properties (especially low boiling point) make it easy to be recovered from the crude oil refineries. Since the surfactant is biodegradable, it won't pose
Table 2 Characterization and FTIR spectra of surfactant extracted from Mahua.
Characterization
FTIR Spectra
Characteristic(s)
Amount
Colour and appearance Specific conductance at 25 °C Specific gravity at 25 °C Total Organic Content (TOC) Non Ionic content Anionic content Cationic content
Brownish red and liquid 73 Microsiemens 1.064 14.32% 10.67% 0.73% 2.92%
Wave Number (cm−1)
Functional group
Range (cm−1)
2157.45 1652.75 1449.23 1379.32 1311.45 1086 721.23
Alkynes Alkenes Alkanes Alkanes Amines Carboxylic acids Alkenes (weak)
2100–2200 1610–1680 1340–1470 1340–1470 1180–1360 1050–1100 675–995
procedures employed by Bhalekar et al. (2017) and Tekin et al. (2016) for extraction of surfactants from soapnut. 50 g of Madhuca longifolia fruits are washed with water and air dried followed by removal of the seeds. The fruits are then vacuum dried to eradicate any moisture left. 300 ml of water was used for refluxing. Skins of Madhuca longifolia were
Fig. 2. FTIR spectra of extracted surfactant Madhuca longifolia (Mahua).
142
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2.4. Experimental setup for flow behavior study
Table 3 Surface tension of heavy oil and its emulsions at different temperatures. Composition
The experimental test section consisted of two horizontal stainlesssteel pipes (SS304) of 0.0381 m and 0.0508 m ID, both of which were 2.5 m in length, water jacket over the pipes surrounded by insulation to minimize heat loss (Fig. 3). Heavy crude oil and coolant (water) temperatures were adjusted to desired values by controlling bath and chilling circulator temperatures. The percentage of water in the crude oil was varied from 0% to 15% while the temperature was varied from 25 °C to 50 °C. For water-in-oil dispersed flow, water and crude oil were mixed in the oil tank with different proportions of water and oil. The concentration of surfactant was varied from 0 to 2000 ppm in the 15% water and 85% heavy crude oil (V/V), while the temperatures ranged from 25 °C to 50 °C and flow rates were measured using digital flow meters ( ± 5%). Pressure drop was measured using a pressure transducer. The oil-water mixture was circulated through an oil pump into the test pipe to perform pressure drop measurements at different flow rates and temperatures.
Temperature Surface Tension mN/m
Heavy oil 95% Heavy 90% Heavy 85% Heavy 85% Heavy 85% Heavy 85% Heavy 85% Heavy
oil oil oil oil oil oil oil
+ + + + + + +
5% water 10% water 15% water 15% water 15% water 15% water 15% water
+ 500 ppm Mahua + 1000 ppm Mahua +1500 ppm Mahua +2000 ppm Mahua
30 °C
40 °C
50 °C
32.5 32.1 31.6 31.2 30.5 30.1 29.6 29.1
31.8 31.5 31.2 30.9 29.9 29.1 28.3 27.8
30.4 30.1 29.7 29.1 28.5 28.1 27.7 27.1
any harm to the environment or possibly corrode the pipeline. Moreover, a low cost of extraction along with the other aforementioned advantages can make the use of this surfactant beneficial in oil industries. Table 3 presents the surface tension of heavy oil with and without water and Mahua at different temperatures. As evident from the table surface tension decreased with temperature, amount of water and Mahua. Surface tension decreases with increase in temperature due to the reduction of cohesive forces with an increased molecular thermal activity. The heavy oil contains organic acids and salts, alcohols and other natural surface-active agents. When the heavy oil is brought in contact with water, these natural surfactants accumulate at the interface and form an adsorbed film which lowers the surface tension of the heavy oil + water emulsion. Surface tension further decreased after the addition of surfactant. The reduction of surface tension of the heavy oil after addition of water and Mahua may be a contributing factor to reduce the pressure gradient by allowing heavy oil to spread out and allowing more water to flow through the near pipe wall (Robert and Vancko, 1997). It may reduce the wall shear stress and also improve the wall depletion effect. A reduction in the surface tension of the oil, with addition of drag reducing agent (DRA), (i.e., surfactant extracted from Mahua in this case) may be a contributing factor in explaining the mechanism of DRA. A reduction in the surface tension allows the liquid film to spread out, allowing more liquid (crude oil) to flow through the pipe. This spreading out of the liquid film resembles annular flow.
3. Results and discussions 3.1. Experimental pressure drop analysis during heavy crude oil flow The impact of diameter and temperature along with novel surfactant on pressure drop and shear viscosity was investigated. Pressure drop was measured by using the pressure transducers at both ends of the test section and the flow rate was measured by using flow meter (Fig. 3). 3.1.1. Effect of temperature and diameter on pressure drop Temperature was the most dominant factor during the pipeline transportation of heavy crude oil. Fig. 4 depicts the effect of temperature on the pressure drop during the transport of heavy crude oil in 0.0381 m and 0.0508 m ID pipelines. It was observed from the experimental results that pressure drops reduced appreciably in both the pipelines with an increase in temperature. As the temperature of the test fluid increases, the viscosity of the heavy crude oil/emulsions decreases which reduces the shear stress between flowing fluid and pipe wall and ultimately improve transportability (Martínez-Palou et al., 2011; Hart, 2014). The impact of flow rate along with temperature was also investigated as shown in the figure. Correspondingly, pressure drop reduced from 0.042 MPa/m to 0.0198 MPa/m (52.85%) and 0.034 MPa/
Fig. 3. Experimental setup pipeline for heavy oil flow.
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is that surfactant can also make a coating over the paraffin and inhibit them to coalesce which may significantly decrease the turbulent frictional factor (Wang et al., 2016). Moreover, wall slip effect is also a very significant contributing factor (Yoshimura and Prudhomme, 1988; Barnes, 1995). It can be concluded that Mahua is partly modifying the pipe wall surface. Thus, Mahua may control the excessive generation and growth of turbulent flow and reduce the pressure drop in all pipelines. Fig. 6 shows the comparison of two surfactants, the surfactant extracted from Madhuca longifolia and a commercial surfactant Tergitol on pressure drop via 0.0381 m ID and 0.0508 m ID pipelines. As evident in Fig. 6, the results are comparable. However, as the novel surfactant is easy to synthesize and easily available, it has an edge over the commercially used surfactant. Table 4 presents a comparison of the data obtained. Natural surfactant Mahua can replace the commercial surfactants to improve the flowability of heavy oils. 3.1.3. Development of friction factor correlations The Fanning friction factor is given by (Guo et al., 2018)
ff =
Fig. 4. Effect of diameter and temperature on the pressure drop during the flow of heavy oil.
2L
D p 2 mix Uavg
(1)
where, D is the diameter of the pipe (m), p is the pressure drop (Pa), L is the length of the pipeline (m), Uavg is the average velocity of the fluid (m/s), and mix is the density of the mixture (kg/m3). Reynolds number and mix are defined as
m to 0.0196 MPa/m (42.35%) when temperature increased from 25 °C to 50 °C during flow of the oil via 0.0381 m ID and 0.0508 m ID pipelines respectively at flow rates of 2.4 m3/h and 3.6 m3/h. The reason for this is suggested due to the reduction of heavy oil viscosity with temperature which reduces the shear stress between the heavy oil and pipe wall during transportation (Hart, 2014). Therefore, heating improves the transportability of heavy oil via pipelines by reducing the viscosity and consequently shear stress at the pipe wall (Saniere et al., 2004; Hart, 2014; Martínez-Palou et al., 2011). It was seen that pressure drop reduced with an increase in diameter at a constant flow rate and temperature. It reduced from 0.0354 MPa/m to 0.026 MPa/m (26.34%) when the inner diameter of the pipeline changed from 0.0381 m ID to 0.0508 m ID at a flow rate of 1.2 m3/hr and 25 °C. As the cross-sectional area of the pipeline decreases (i.e., at constant length) the velocity of the fluid in the narrower pipeline increases in order to maintain constant flow rate (i.e., Bernoulli's equation). This increased fluid velocity reduces the static pressure (Çengel and Cimbala, 2013). Similarly, if the inner diameter of the pipeline increases, the velocity of the fluid decreases to maintain a constant flow rate, which increases the static pressure. Therefore, the pressure drop decreases with an increase in the inner diameter (ID) of the pipeline at a constant flow rate and temperature (i.e., from 0.0381 m ID to 0.0508 m ID).
Rem =
mix
=
DUavg
mix
(2)
µshear o
+ (1
)
w
(3)
where, µshear is the shear viscosity (Pa.s), o and w are the densities of oil and water (kg/m3), and is the volume phase fraction of oil (%). The relation between friction factor and Reynolds number is shown in Fig. 7 (A-C) by using equations (1) and (2). It was observed that friction factor reduced with the amount of dispersed water and addition of natural surfactant in each temperature which is an analogous representation to the pressure drop. It was also seen that all the friction factors are in-line with the Reynolds number. Correlations were developed by using linear regression analysis for heavy crude oil flows without and with water and natural surfactant and shown in equations (4)–(6) respectively [Fig. 7(A-C)].
3.1.2. Impact of diameter and surfactant on pressure drop The impact of surfactant addition on pressure drop at different temperatures in both the pipelines is depicted in Fig. 5 for only crude oil flow in each pipeline. The addition of novel surfactant in water reduced the pressure drops effectively during the flow of crude oil in each pipeline. It was also observed that the minimum pressure drops were obtained after addition of 2000 ppm of Mahua to 85% heavy crude oil +15% water. Pressure drop reduction of 55.18% (0.027 MPa/m to 0.0121 MPa/m), and 76.12% (0.0272 MPa/m to 0.0065 MPa/m) was achieved in 0.0381 m (6.6 m3/hr) and 0.0508 m ID (7.2 m3/hr) pipelines respectively after addition of 15% water and 2000 ppm Mahua to heavy oil. High pressure drops occur during the flow of crude oil at low temperatures. High-pressure drop in a pipeline is unfavorable from the industrial point of view due to high pumping power requirement. The addition of Mahua may improve the pressure drop reduction by the forming rod-shaped micelles with shear degradation resistance performance. These rod-shaped micelles can absorb the excess energy of the turbulent flow (i.e., the generated shear stresses at the pipe wall surface) (Wang et al., 2016). The other reason for pressure drop reduction
f f ,0.0381m =
31.71 Re1.076 m
(4)
f f ,0.0508m =
28.4 Re1.114 m
5)
f f , all pipe =
24.2 0.9945 Rem
(6)
These correlations show that friction factors are diameter dependent. The friction factor generally decreases with the increase in the Reynolds number, especially at high concentrations of water and surfactants. Fig. 7 (A1-C1) depicts the percentage deviation of the experimental predicted values from equations (4)–(6). The results show that equations (4) and (5) depict deviation of ± 10% and equation (6) shows ± 20%. 3.1.4. Uncertainty in measurement The uncertainty in measurements was carried out on the pressure drop measurements. Quantitative measurements on pressure drop during the heavy oil transportation at different flow rate tend to be normally distributed. The SD (Standard Deviation) and SE (Standard Error) were determined using equations (7) and (8) respectively 144
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Fig. 5. Effect of Mahua on pressure drop during flow of heavy oil at 30 °C.
Fig. 6. Comparison of natural (Mahua) and commercial (Tergitol) surfactants on pressure drop in two pipelines to 85% HO + 15% W at 35 °C.
Table 4 Comparison of natural and commercial surfactant on pressure drops during the flow of 85% Heavy crude oil +15% Water at 5 m3/hr at 35 °C. Sl. No
Concentration, ppm
(Pressure gradient), MPa/m 0.0381 m-ID pipeline
1 2 3 3
500 1000 1500 2000
0.0508 m-ID pipeline
Mahua
Tergitol
Variation%
Mahua
Tergitol
Variation%
0.0251 0.0215 0.0207 0.0181
0.0242 0.0222 0.0197 0.0191
3.58 3.25 4.83 5.52
0.0169 0.0149 0.0132 0.0116
0.0176 0.0147 0.0133 0.0119
4.14 1.348 0.75 2.58
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Fig. 7. Correlation development for friction factor using Reynolds number (A–C) Percentage deviation of the experimental and friction factor equations (A1-C1).
Fig. 8. Uncertainty analysis (standard error) of pressure drop measurements.
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additive concentrations (Keleşoǧlu et al., 2012). The consistency index (K) shows the opposite change to the flow behavior index (n) (Fig. 9). The decrease in consistency index (K) and an increase in the flow behavior index (n) were achieved with an increase in temperature, water cut, and additives concentration (Fig. 9). The flow behavior index (n) represents the degree of non-Newtonian characteristic of the heavy oil/ emulsions. This decrease in consistency index (K) and an increase in flow behavior index (n) represents the decrease in the viscosity of the heavy oil/emulsions. Significant improvements in rheological behavior near the pipe wall have been observed after addition of Mahua (Fig. 9). The additive Mahua effectively reduced the consistency index (K) and increased the flow behavior index (n) during the flow of 85% heavy oil15% water via pipelines. After addition of Mahua to the heavy oil-water emulsions flow behavior index values tend towards unity (i.e., Newtonian behavior). This shows that the fluid changes its operational rheological behavior towards Newtonian behavior from shear thinning behavior with an increase in temperature, the volume of water, and the concentration of additive.
Table 5 Parameters of uncertainty analysis. Parameter
Value
Mean Standard Error Standard Deviation Sample Variance Kurtosis Minimum Maximum Confidence Level (95.0%)
2.042E-02 2.574E-04 7.563E-03 5.719E-05 −4.768E-01 3.585E-03 4.109E-02 5.053E-04
n i=1
SD
p
=
SE
p
=
SD
¯p L
pi L n
(7)
p
(8)
n
3.2.2. Effect of Mahua on shear viscosity Fig. 10 presents the effect of the Mahua on shear viscosity during the flow of 85% heavy oil +15% water in 0.0381 m ID, and 0.0508 m ID pipelines. As seen in Fig. 10 shear viscosity reduced after addition of Mahua in all the pipelines. It was also observed that the in-situ rheological behavior of 85% heavy oil+ 15% water tends to move towards Newtonian from the shear thinning behavior (n = 0.2181 to 0.9834) after addition of 2000 ppm Mahua at 50 °C. Viscosity reduction capacity of Mahua in comparison to other surfactants and solvents reported in the literature is shown in Table 6. Viscosity reduction data obtained with the surfactant is comparable with those from literature. Due to paraffin dissolution and diminishing of the excessive energy (i.e., for generated shear stresses at pipe wall surface) capabilities of Mahua, and with promotion of wall depletion effect can reduce the shear viscosity in all pipelines. Therefore, the addition of Mahua improves the operational rheological behavior during the transportation of 85% heavy oil +15% water in pipelines effectively.
th
where n is the sample size, pi is the pressure drop of i measurement, and p is the mean pressure drop from measurements. Fig. 8 depicts the standard error for the pressure drop measurement. The standard deviation of 7.563 × 10−3 and standard error of 2.57 × 10−4 was seen for the pressure drop measurements from the experimental setup (Table 5). This means that the investigations of pressure drop produced very low errors. 3.2. Studies on shear viscosity during pipeline flow of heavy crude oil/ emulsion During the of heavy oil transportation in pipelines, shear (i.e., operational) rate, shear viscosities, and flow behavior index were calculated using pressure drop and flow rates equations described by the Gudala et al. (2018).
n=
wall
a
=
d log( w ) d log( a )
(9)
p x
(10)
=
D 4
4Q D3
µshear = K
3.3. Effect of water cut, and mahua on flow development The mechanism of flow development using hydrodynamic entry length is explained in previous works. The distance from the entry to the maximum velocity (disappearing point of boundary layer) location is called the hydrodynamic entry/entrance length (Gudala et al., 2018). During transportation of fluid in horizontal pipes, hydrodynamic entry length depends not only on the Reynolds number but also on water cut and surfactant concentration. In this research hydrodynamic entry length was investigated at different flow rates, temperature, water cut and surfactant concentrations in the heavy crude oil. The hydrodynamic entrance length is calculated by using a correlation given by Durst et al. (2005) in equation (13). Correlation with exponents for a wide range of Reynolds number (0 < Rem < ) was developed by Durst et al. (2005) using numerical investigations which showed an error of 3% under suggestions of Churchill and Usagi (1972) where asymptotic behavior of hydrodynamic entry lengths was considered.
(11)
3n + 1 4n
n 1
32Q D3
n 1
(12)
where w wall shear stress (Pa), a is apparent wall shear rate (s−1), K is consistency index (Pa.sn), n is flow behavior index, Q is flow rate (m3/hr). 3.2.1. Effect of temperature, water cut and additives on consistency index (K) and flow behavior index (n) Viscosity is one of the crucial parameters of a fluid to be transported via pipelines. During the transportation of heavy crude oil (i.e., operational) shear rate (equation (11)) and shear viscosities (equation (12)) were calculated from the pressure drop and flow rate. For a real fluid, many flow models are present in the literature which relate viscosity with the shear stress (equation (10)) and shear rate. Fig. 9 presents the Power law model constants during the transportation of heavy oil after adding water and additives at a different temperature. To suggest whether a fluid is Newtonian or non-Newtonian, sometimes consistency index (k) and flow behavior index (n) is employed. A fluid is likely to show Newtonian characteristics if its flow behavior index is close to unity and consistency index has high values, and vice versa. The consistency index (K) (equation (12)) and flow behavior index (n) (equation (9)) are dependent on the temperature, water cut and
Lh = [0.6191.6 + (0.0567 Rem)1.6 ]1/1.6
(13)
Equation (13) is valid in the range of 0 < Rem < . At constant flow rate and diameter, Reynolds number was dependent on the density and shear viscosity of the heavy oil and its emulsions. It was seen that hydrodynamic entrance lengths (i.e., flow developing length) increased with the temperature of the flowing fluid at a constant flow rate (Fig. 11). It is due to variation in shear viscosity of the heavy oil with temperature. The hydrodynamic entrance lengths increased gradually with increasing water cut in the heavy oil at a constant flow rate. This may be due to the increasing wall depletion effect during crude oil flow after the addition of water in both the pipelines. It reduces the shear 147
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Fig. 9. Consistency index (K) and flow behavior index (n) of the heavy oil (HO) during the transportation in 0.0381 m ID and 0.0508 m ID pipelines at different temperatures, water cut (W) and Mahua concentration.
Fig. 10. Effect of mahua on shear viscosity during heavy oil flow through 0.0381 m ID and 0.0508 m ID pipelines at 45 °C. 148
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Table 6 Comparison of viscosity reduction capacity of Mahua with different solvents and surfactants. Sl. No I 1 2 3 4 5 6 7 8 9 10 II 11 12 13 14 15 16 17 18 19 20 21 22 23
Additive Solvent addition Xylene Xylene Toluene Benzene Emulsion Emulsion Light oil PRCW E1 Light crude oil Light Oil Surfactant addition EVA-80 EVA-80 EVA-80 EVA 32 EVA 32 EVA 32 EVA 32 EVA 32 E1T6 E3T6 Copolymer of ethylene and vinyl acetate 15% water and Mahua 15% water and Mahua
Amount of additive added
% viscosity reduction
Temperature, °C
Reference
5% v/v 3% v/v 5% v/v 5% v/v 10% v/v 20% v/v 10% v/v 5% v/v 30% v/v 50% v/v
27 22 26 24 11.5 49 87 77.9 98% 55%
40 40 40 40 45 45 45
Taraneh et al. (2008)
50 40
2000 ppm 2000 ppm 2000 ppm 2000 ppm 2000 ppm 2000 ppm 2000 ppm 2000 ppm 1000 ppm 1000 ppm 1000 ppm 2000 ppm 2000 ppm
88 78 58 64 85 52 28 29 17.69 12.05 22.1 48.9 57.5
20 15 10 40 20 15 10 5 40 40 40 45 45
Hasan et al. (2010) Etoumi (2007) Yaghi and Al-Bemani (2002) Ashrafizadeh and Kamran (2010) Taraneh et al. (2008)
Hafiz and Khidr (2007) Pedersen and Rønningsen (2003) This work (at 200 s−1 in 0.0381 m ID pipeline) This work (at 100 s−1in 0.0508 m ID pipeline)
for the fluid to obtain improved flow behavior.
viscosity and increases the hydrodynamic entrance length (Lh). It was also seen that Mahua has a significant effect on the hydrodynamic entrance lengths. It is due to the promotion of wall depletion effect after the addition of Mahua to the 85% heavy oil +15% water during the flow. The maximum hydrodynamic length was observed at 50 °C and 2000 ppm of mahua to the 85% heavy oil + 15% water during transportation in each pipeline (Fig. 11). This increase in hydrodynamic entrance length shows that the boundary layer develops slowly after addition of the water and mahua to the heavy oil at a constant flow rate and temperature. Therefore, the addition of water and mahua to the heavy oil slow down the boundary layer development by reducing the shear viscosity (i.e., hydrodynamic entrance length increase). As a result, the hydrodynamic entrance length will increase giving more time
3.4. Pumping power requirements for the flow of crude oil Instead of using a greater number of pumps and/or looping, surfactant addition is a preferable choice to increase transportation efficiency. Investigation of the pumping power of the system was done to explore this fact. Saving in pumping power was investigated in terms of head loss before and after addition of Mahua at different flow rates. The percentage of drag reduction in terms of friction factor was defined as
%DR = 1
fMahua f
× 100
Fig. 11. Effect of temperature, water cut, and Mahua on the hydrodynamic entrance length (Lh) during the flow of heavy oil via pipelines at flow rates. 149
(14)
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Fig. 12. Pumping power saving during the transportation of Heavy oil after the addition of water and Mahua at different flow rates and temperatures.
where, fMahua is friction factor after addition of Mahua and %DR is the drag reduction percentage. Head loss is calculated by simultaneous consideration of drag reduction (equation (14)) and Darcy-Weisbach equation. The relation between head loss before and after addition of Mahua was defined as
hL
Mahua
%DR × hL 100
= 1
diameter after addition of water and Mahua during the flow of heavy oil. Maximum pressure drops were achieved in 0.0381 m ID pipeline (at 25 °C) and minimum pressures drop occur in 0.0508 m ID pipeline during the flow of 85% heavy oil + 15% water after addition of 2000 ppm of Mahua at 50 °C. Mahua shows better pressure drop reduction capabilities due to its encouraging abilities such as modifying the pipe wall surface, control of excessive generation and growth of turbulence via pipelines. Correlations were developed by using the linear regression analysis to predict the friction factors with and without water and bio-additive for heavy oil transportation. The developed correlations show good agreement with the experimental results (i.e., deviation ± 10% and ± 20%). Minimum shear viscosity was detected in 0.0381 m ID and maximum occurs in 0.0508 m ID pipeline during the transportation of heavy oil at 50 °C and 25 °C respectively. Maximum flow behavior index of 0.9843 was seen after addition of 2000 ppm Mahua to the crude oil at 50 °C via 0.0508 m ID pipeline. Mahua showed excellent capabilities to improve the pumping power requirement saving and flow increments. The extracted novel natural surfactant is highly beneficial for being used as an emulsifier, pressure drop reducer, flow improver and decreasing the pumping power consumption.
(15)
where, hL is the head loss (m). The extracted surfactant reduced the friction and consequently the pumping requirement of this crude oil changed. The saving in pumping power requirements overcomes the head loss as a result of added surfactant at each flow rate and temperature can be expressed as follows (Al-Wahaibi et al., 2017)
Wps =
g (hL
hL
Mahua)
× QT
(16)
where Wsp is the saving in power required (%) and QT is the total volumetric flow rate (m3/hr). Fig. 12 depicts the percentage savings in the pumping power requirements during flow as a function of surfactant concentration with a flow rate ranging from 2.4 to 6.6 m3/hr (i.e., for 0.0381 m ID), 3-7.2 m3/hr (i.e., for 0.0508 m ID) and temperature ranging from 25 °C-50 °C. It can be seen that after the addition of Mahua to 85% heavy crude oil + 15% water, the amount of power saved increased progressively in all pipelines. Power saving was achieved to about 128.7% (6.6 m3/hr) and 130.8% (7.2 m3/hr) during the 85% heavy oil + 15% water transportation at 50 °C after addition of 2000 ppm Mahua in 0.0381 m, and 0.0508 m ID pipelines respectively. Results also show that the percentage of power saved increased with an increase in flow rate and temperature in all pipelines and decreased with an increase in inner diameter of the pipeline (Al-Wahaibi et al., 2017). This increasing pumping power saving is due to the fact that flow rate would increase the turbulence intensity which enhances the performance of Mahua by increasing the drag reduction, wall depletion effect (Al-Wahaibi et al., 2017; Santos et al., 2014a,b).
Acknowledgment IIT (ISM), Dhanbad, India, [FRS (42)/2012–2013/PE] and DST (SERB), India [Project no:EEQ/2016/00650], The authors would also like to thank ONGC Ltd, India for supplying the heavy crude oil. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.petrol.2019.03.027. References
4. Conclusions
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