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Optimization of effective sulfur solvents for sour gas reservoir
Journal of Natural Gas Science and Engineering 36 (2016) 463e471
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Optimization of effective sulfur solvents for sour gas reservoir Jincheng Mao a, *, Xiaojiang Yang a, Dingli Wang a, Yang Zhang a, Suzhou Luo a, Gregory S. Smith b, Yongming Li a, Jinzhou Zhao a, ** a b
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, PR China Department of Chemistry, University of Cape Town, P. Bag X3, Rondebosch, 7700 Cape Town, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 May 2016 Received in revised form 17 October 2016 Accepted 22 October 2016 Available online 23 October 2016
Sulfur deposition attracts great attention for the exploration of oil and gas and is considered one of the most important hazardous processes in China, and all over the world. Thus, investigating a sulfur solvent is absolutely necessary and highly desirable in the sour gas reservoir development. In recent years, various sulfur solvents were developed and applied in different oilfields. However, they have disadvantages in their practical applications. In this paper, a solution is proposed to solve the problem and improve the sulfur dissolving ability. Three types of sulfur solvents were prepared, all of which have their own characteristics and advantages in different cases and compared with the existing sulfur solvents under the same conditions. The solubility of Dimethyl disulfide(DMDS)-based sulfur solvent system was up to 202.8 wt% at room temperature and 1020.0 wt% at 90 C. Amine solvent systems also achieved high sulfur solubility. The solubility of diethylene triamine-ethanolamine solvent system could reach 79.6 wt% at room temperature and 210.0 wt% in 90 C. It was shown that a more efficient sulfur solvent system can be achieved by remixing with suitable additives. This paper focuses on a preliminary study of optimizing effective sulfur solvents in order to solve the problems caused by sulfur deposition. In the long run, this may revolutionise the process of exploration, transportation and refining of crude oil or natural gas. Microscopic analysis by Scanning Electron Microscope (SEM) was used to facilitate understanding the mechanism of sulfur dissolution in each system and their differences. © 2016 Elsevier B.V. All rights reserved.
Keywords: Sulfur solvent DMDS Diethylene triamine Propylamine Phase transfer catalyst
1. Introduction Sour gas reservoirs are the most important composition of unconventional oil and gas reservoirs, and are widely distributed in China, even all over the world. According to statistical information mentioned in “Sour gas field development technology information publication (edited by China Petroleum and Chemical Corporation)”, more than 300 sour gas fields with industrial value have been discovered all over the world, especially in Russia and Canada, as well as in America, Germany and France. Sour gas is a type of acidic gas which contains 5 ppm H2S, but in China, 60% gas fields contain 20,000e40,000 ppm H2S, some are more than 100,000 ppm. For instance, the proved reserve of Puguang Gas Field is 114.363 billion m3 and the recoverable reserve is 87.832 billion m3, but it contains 1,195,000 ppm. In such gas reservoir
* Corresponding author. ** Corresponding author. E-mail address: [email protected] (J. Mao). http://dx.doi.org/10.1016/j.jngse.2016.10.034 1875-5100/© 2016 Elsevier B.V. All rights reserved.
development processes, accompanied with the gas flow, the elemental sulfur would be easily deposited as the condensate in the form of sulfur, especially when the pressure and temperature were reduced (Zeng et al., 2012; Lyle et al., 1978; Clark et al., 1989; Guo et al., 2015; Hu et al., 2011, 2014a). The reservoir and gathering pipeline can become plugged by such deposition of the sulfur, which seriously affects the production of gas well (Li et al., 2011a). In addition, steel can be seriously corroded by mixtures of sulfur and water. Gathering pipeline and casing would perforate and damage, wells may be shut down or even scraped when corrosion becomes too serious. Worst of all, natural gas leakage caused by it would lead to serious environmental pollution and harmful to human health. It is understood that sulfur usually exists in the form of hydrogen sulfide as a natural gas and hydrogen sulfide is highly toxic. Thus, losses brought by it could not be estimated. For example, a sour gas well blowout occurred in Kaixian county of Chongqing in China on December 23, 2003, injuring more than 93,000 people and killing 243 people. Direct economic losses reached nearly 82 million RMB, while indirect economic losses are
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
uncountable. Further to that, hydrogen sulfide leakages occur on a yearly basis in sour gas fields all over the world and kill people through leaks caused by pipeline damage. In order for sour gas reservoirs to be economical, a practical and economical method needs to be developed for exploiting these reservoirs. The problem needs to be solved urgently and it is absolutely necessary to carry out the research to develop sulfur dissolving technology and develop novel, efficient and low-cost sulfur solvent systems to prevent sulfur deposits in pipeline and ensure gathering pipeline work properly (Demirbas et al., 2015; Hilzman and Dennis, 1998; Nasr-El-Din and Al-Humaidan, 2001; Wilken, 1991; Hu et al., 2014b; Mahmoud, 2014; Hassan and Behnam, 2015). Herein, three kinds of sulfur solvents will described for different conditions. 2. Experimental and calculation method
that an aromatic ring can improve the sulfur solubility. It is therefore necessary to study the sulfur solubility of benzene derivatives. 3.1.2. Screening of benzyl solvents The results of the study on sulfur solubility of benzyl solvents are shown in Fig. 2. It can be seen that the sulfur solubility of styrene is higher than the other benzyl solvents. A comparison of the sulfur solubility of toluene and chlorobenzene shows that the CeCl bond can significantly increase the sulfur solubility. However, a comparison of styrene and chlorobenzene indicates that the double bond is more crucial to the sulfur solubility than CeCl bond. Unfortunately, styrene is easily volatilised at high temperatures (Zhang and Xia, 2012). The sulfur solubility of xylene is higher than styrene at 80 C. Considering the volatility and price of benzyl solvents, xylene would be employed in further screening experiments.
2.1. Experimental method A round bottom flask was charged with a given amount of elemental sulfur and solvent. The mixture was stirred with constant speed for 2 h. The undissolved sulfur could be recovered by filtration and dried in an oven at constant temperature (40 C) for 24 h. Then it was weighed for calculating the sulfur solubility. Sulfur dissolving experimental conditions: 25 C, 0.1 MPa. 2.2. Sulfur solubility calculation method It is well known that solubility is defined as the percentage of solute dissolved in the unit mass solvent. It is mathematically described by:
Y¼
M1 M2 100% M
(1)
where Y ¼ solubility of the solvent, M ¼ amount of the solvent, M1 ¼ initial amount of the sublimed sulfur, M2 ¼ final amount of the undissolved sublimed sulfur. 3. Screening experiment 3.1. Screening of main solvents In the experiments of main solvents screened, the amount of each solvent was set to 25 g. A given amount of sulfur was added to the solvent and ensured that it was saturated by sublimed sulfur, then calculating the solubility using the formula above. 3.1.1. Screening of common solvents The sulfur solubility in various common solvents was tested and the corresponding results are shown in Fig. 1. The results show that the solubility of DMDS is significantly higher than the other solvents. The difference of sulfur solubility might be relative to the chemical structures of solvents. DMDS is a stable pale yellow liquid which works as an effective product in the sulfide process because of its high sulfur content. It is also the sulfiding industry's reagent of choice because it offers more sulfur per pound of reagent when compared to its nearest competitor dimethyl sulfide. Initially, it is assumed that the sulfur and ether bond of DMDS may be attributed to its high solubility. However, DME which has an ether structure gave poor results. This is indicative that the sulfur bond will play a more important role to promote the sulfur solubility of the solvent and its dissolution mechanism can be explained as “like dissolves like”. Sulfur reagents usually have bad smell. With the various demands of oilfields, alternative sulfur solvents should be further explored. A comparison of dichloromethane and xylene indicates
3.1.3. Screening of amine solvents Amine solvents have been studied by many researchers. For example, Liu and co-workers revealed that diethylene triamine may be a possible candidate as a sulfur solvent (Liu et al., 2008a, 2008b). To acquire more efficient soluble systems, it is necessary to perform extensive research on amine solvents. Thus, thirteen amine solvents were chosen to test their sulfur solubilities, as shown in Fig. 3. In a different approach, the process of reacting anmine solvents with sulfur results in the release much heat and thus, an increase in the temperature of the solution, will lead to higher sulfur solubility. Notably, the sulfur solubility of diethylene triamine or propylamine is significantly higher than DMDS at room temperature. By raising the temperature, the dissolution rate of triethylene tetramine became faster than diethylene triamine. In 2014, Guo and coworkers found that the sulfur dissolution rate of triethylene tetramine was 24.65 g/min/L and diethylene triamine was only 22.25 g/ min/L (Guo, 2014). However, the sulfur solubility of diethylene triamine was higher than triethylene tetramine albeit at higher temperatures or room temperature. Therefore, it is incorrect to generally conclude that more amine groups in molecules can afford higher sulfur solubility. A comparison of ethanolamine, diethanolamine and triethanolamine indicates that a hydroxy group is unfavorable for the sulfur solubility. It can be seen that the sulfur solubilities of diethylene triamine and propylamine are both beyond 28 wt%. However, we found that during the course of filtration, the solution of diethylene triamine was too sticky to handle. In addition, the boiling point of propylamine is very low (about 48 C) and thus it is recommended to be used at room temperature. In order to reduce the viscosity of diethylene triamine sulfur solution, mixed solvent experiments were designed. Other solvents were set to 50 wt% of diethylene triamine and the relative results are shown in the Table 1. In view of the high price of DMDS and high volatility of propylamine, ethanolamine will be most suitable to reduce the viscosity of diethylene triamine sulfur solution and the optimal proportion was found to be 2:1 (diethylene triamine: ethanolamine). 3.1.4. Comparative analysis It can be seen from the above screening experiments that DMDS, diethylene triamine and propylamine are the most promising candidates as the efficient sulfur solvents. Besides the difference of solubility, some other phenomena were noticed during the course of experiments. The appearance of most of filtering sulfur is similar to the sublimed sulfur and sometimes the color becomes light. However, for the benzyl solvents, especially for benzene and chlorobenzene, some black particles were found in the filtering
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
Fig. 1. The solubility of common solvents.
Fig. 2. The sulfur solubility of benzyl solvents.
Fig. 3. The solubility of amine solvents.
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471 Table 1 Cosolvent screening experiments. Cosolvent
Initial sulfur (g)
Undissolved sulfur (g)
Filtering time (min)
Phenomenon
DMDS propylamine ethanolamine ethylenediamine triethylenetetramine xylene methyamine diethylene Driethylenediamine isopropylamine
7 7 7 7 7 7 7 7 7 7
0 0 0 0.71 12.02 15.04 15.35 16.48 19.71 19.84
10 15 16 14 20 20 20 20 20 20
turn turn turn turn turn turn turn turn turn turn
black black black black, layered black black, layered black black black black, layered
cakes as shown in Figs. 4e5. It is noteworthy that for the amine solvents, the color of the system significantly changed to brown after dissolving the sulfur, as shown in Fig. 6. It can be assumed from this special phenomena that black particles and dark viscous materials may be caused from their chemical reactions between them, to form some intermediates or complexes. Further determinations based on modern physical machines are underway in our laboratory.
3.2. Screening of various additives
Fig. 4. Filtering products of xylene sulfur solution.
Fig. 5. Filtering products chlorobenzene sulfur solution.
SULFA-HITECH which is an efficient sulfur solvent was prepared by Pennwalt of America in 1988 by adding a small amount of inorganic base (sodium hydrosulfide) and DMF to DMDS. However, the organic base-amine solvents were found efficient as sulfur solvents in the above experiment (Liu et al., 2008b). Therefore, the screening of organic and inorganic bases is extremely necessary. Xylene was used as the main solvent for the screening experiments in view of its low price. Results of the experiments are shown in Table 2. It can be seen that quinoline (organic bases) and sodium hydrosulfide (the inorganic bases) can significantly improve the sulfur solubility of xylene. A phase transfer catalyst (PTC) is a type of catalyst which is helpful to transfer reactants from one phase to another phase, making it easier to perform the reaction in a heterogeneous system (Starks, 1987). In principle, it is most likely improve the sulfur dissolving ability of sulfur solvents. Thus, PTCs were screened in a mixed solution of xylene and quinoline. Finally, it was found that 18-crown-6 was the only catalyst which can improve sulfur solubility of the solution. Detailed data of experiments are listed in Table 3. Furthermore, the efficient additive could enhance intermolecular forces of S8 by a large p bond, forming sandwich structures and thus improving the sulfur solubility of the system. Ferrocene is one such kind of sandwich complex which has an aromatic property, high boiling point, stable physical and chemical properties. The results of the experiment showed that ferrocene is a better phase transfer catalyst (18-crown-6) on the aspect of improving solubility of sulfur solvents. Therefore, it would make sense to mix these together with 18-crown-6 and other solvents, in an effort to achieve more efficient sulfur solvent systems.
4. The formation of formula
Fig. 6. Filtering products of diethylene triamine sulfur solution.
The formula of a sulfur solvent system depends on not only the suitable additives, but also on a certain ratio. The following experiments detail the various components of the system.
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471 Table 2 Screening experiments of various bases. Organic bases
Solubility (%)
Inorganic bases
Solubility (%)
quinoline DMAP pyridine hydroxyquinoline Propylamine triethylenediamine ethanolamine indole pyrazole N,N-dimethylaniline triethylenetetramine triethylamine blank piperidine 2-amino-6-chlorobenzothiazole diethylamine melamine diethylene triamine
3.36 3.32 3.24 3.16 3.16 3.04 3.00 2.92 2.80 2.76 2.76 2.72 2.72 2.64 2.60 2.48 2.44 2.00
sodium hydrosulfide sodium sulfide sodium sulfate sodium bisulfite sodium sulfite sodium thiosulfate sodium acetate sodium salicylate sodium bisulfate sodium bicarbonate blank disodium hydrogen phosphate sodium hydroxide sodium dihydrogen phosphate sodium persulfate sodium formate sodium carbonate
3.56 3.36 3.28 3.24 3.04 3.00 2.96 2.96 2.88 2.76 2.72 2.64 2.60 2.52 2.48 2.20 2.04
Table 3 Screening experiments of various phase transfer catalysts. PTC
Solubility (%)
Special phenomenon
18-Crown-6 blank cetyltrimethylammonium chloride Tetrabutylammonium chloride Tetramethylammonium chloride tetramethylammonium silicate Tetrabutylammonium acetate Tetramethylammonium Iodide PEG-400 dodecyl trimethyl ammonium bromides cetyltrimethylammonium bromide PEG-1000 PEG-2000 tetrabutylammonium bromide tetrabutylammonium iodide
3.52 3.36 3.16 3.08 3.04 3.00 2.88 2.88 2.72 2.36 2.32 2.32 2.24 2.20 2.00
nothing nothing nothing nothing nothing nothing nothing white precipitation black phase and points structure nothing black massive and flake structure white precipitation white precipitation nothing nothing
4.1. DMDS solvent system 4.1.1. Screening of auxiliaries It was found that auxiliaries can significantly improve sulfur solubility of a DMDS sulfur solvent by studying existing DMDS systems. Selecting a suitable auxiliary is extremely necessary to prepare an efficient sulfur solvent. In an auxiliary screening experiment, DMDS was set to be 5.0 g, sodium hydrosulfide was 0.5 wt% and the auxiliary was 5.0 wt%. Information from the results shown in the Fig. 7, indicate that DMSO is the best and it is slightly better than DMF used under the same conditions. 4.1.2. The formation of formula To our surprise, we found that quinoline would inhibit the solubility of a DMDS system. Thus, the preliminary DMDS system formula will consist of DMDS, DMSO and sodium hydrosulfide. However, the ratio of the composition in the system would greatly affect solubility of the sulfur solvent. The ratio of each reagent was determined by experiment: DMDS, DMSO (5.0 wt%) and sodium hydrosulfide (0.5 wt%). Results of the experiments are shown in Table 4. Based on the result of the above basic screening experiments, the ratio of the phase transfer catalyst and additive was studied. Results of the experiments are shown in Table 5 and the final formula of DMDS sulfur solvent system were DMDS, DMSO (5.0 wt%), sodium hydrosulfide (0.5 wt%), 18-crown-6 (1.0 wt%) and ferrocene
Fig. 7. Auxiliary solvents for DMDS system.
Table 4 Result of preliminary complex formulation experiment. DMSO (%)
5.00
5.00
2.50
2.50
Sodium hydrosulfide (%) Solubility (%)
0.50 168.2
1.00 154.0
0.50 150.8
1.00 135.2
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
(1.0 wt%). It can be seen from the table that the sulfur solubility of the system could reach 202.8 wt% at room temperature.
Table 5 Effect of catalysts on the solubility of DMDS solvent system. catalyst
Solubility (wt%)
18-crown-6 (wt%)
Ferrocene (wt%)
1.0 0.0 1.0 0.0
1.0 1.0 0.0 0.0
4.2. Amine solvents system 202.8 170.6 169.4 168.2
Table 6 Result of remixing with alkaline system. alkaline
Solubility (wt%)
quinoline sodium hydrosulfide
Propylamine
Diethylene triamine
65.4 68.2
63.8 65.2
75
Diethylene triamine Propylamine
70
Solubility (wt%)
65 60 55 50 45 40
5. Performance evaluation
0
1
2
3
4 5.1. Effect of temperature on sulfur solvent system achieved above
Ratio of sodium hydrosulfide (wt%) Fig. 8. Ratio determination of amount NaHS.
85
Propylamine Diethylene triamine
80 Solubility (wt%)
Propylene and diethylene triamine-ethanolamine were found to be efficient sulfur solvents in the above screening experiments. Thus, remixing experiments of amine solvents were investigated. The results listed in Table 6 indicate that quinoline and sodium hydrosulfide can significantly improve the solubility of amine solvents. In the experiment concerning formula formation of amine solvents and sodium hydrosulfide, it was found that the sulfur solubility was highest when sodium hydrosulfide accounts for 1.0 wt% of amine (propylamine and diethylene triamine) solvents. The results of the experiment are shown in Fig. 8. Based on the above research, NaHS was set to be 1.0 wt% of amine solvents, and the amount of quinoline was screened. Results are shown in Fig. 9 and it can be seen that the most suitable amount of quinoline is 2.0 wt% of the amine solvents. Considering the accelerated role of ferrocene and 18-crown-6 in improving the sulfur solubility of DMDS system, their effects on amine solvents were investigated carefully. In the experiments, amine solvents were set to be 5.0 g, sodium hydrosulfide was 1.0 wt% and quinoline was 2.0 wt%. Results are shown in Table 7. It can be observed that ferrocene and 18-crown-6 could not improve the solubility of the amine solvents, but inhibit the dissolving ability. Finally, the ratio of the amine sulfur solvent systems were determined to be as follows: propylamine, sodium hydrosulfide (1.0 wt%), quinoline (2.0 wt%), diethylene triamine-ethanolamine, sodium hydrosulfide (1.0 wt %), and quinoline (2.0 wt%). The solubility of propylamine system reached 80.4 wt% and the diethylene triamine system reached 79.6 wt% at room temperature.
75
70
Considering the volatility of propylamine, only the effects of temperature on DMDS and diethyllene triamine systems were investigated. Based on the optimal ratio of the reagents, sulfur dissolution experiments were analyzed at 25, 80 and 90 C. Results of the experiments are shown in Fig. 10. Information gleaned from the figure indicates that the solubility of the sulfur solvent systems increases with an increase in temperature. Notably, an increase in the amount of the DMDS system was most significant. The sulfur solubility of DMDS reached 1020 wt% at 90 C, which is the best result thus far. Upon increasing temperature, the reaction constant of sulfur dissolution is increased, which enhances the sulfur dissolving ability (Schmitt, 1991). In addition, polysulfide which is generated from DMDS and sulfur could further dissolve sulfur. Comparatively, the
Table 7 Screening important additives. Additives
65
0
1
2
3
Ratio of quinoline (wt%) Fig. 9. Ratio determination of quinoline.
4
Solubility (wt%)
18-crown-6 (wt%)
Ferrocene (wt%)
Propylamine
Diethylene triamine
0.0 1.0 0.0 1.0
0.0 1.0 1.0 0.0
80.4 77.6 64.4 63.8
79.6 75.4 63.2 62.8
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
the solvents, and the mechanism of dissolution.
5.3. Microscopic analysis and comparison
Fig. 10. Effect of temperature on the solubility of solvents.
temperature does not show such a dramatic influence on the solubility of the amine solvent system (210 wt% in 90 C). To this end, the solubility has been improved because of the raised temperature. The relative mechanism is underway in our laboratory.
Microscopic analysis aimed at facilitating the understanding of the mechanism of sulfur dissolution in each system and their differences, is as shown in Fig. 12. Compared with elemental sulfur, it was found that residual particles of the DMDS system had a low dispersion and large agglomerates due to solvent invasion. Elemental sulfur was dissolved in the DMDS system by being encapsulated and forming an emulsion liquid system. The residual of elemental sulfur in propylamine system could also be examined. However, these particles were more regular than the particles in the DMDS system and their shapes look like monocline crystal of sulfur. It is estimated that solid sulfur was composed of rhombic sulfur and monocline crystals of sulfur. Moreover, rhombic sulfur is recrystallized and thus dissolved more easily than monocline crystal of sulfur. The propylamine system was preferential to dissolve rhombic sulfur of solid sulfur. The residue of the diethylene triamine system was a quite different sticky material, a new resultant and we could not find solid particles at the same discharge rate. Elemental sulfur may be dissolved to smaller particles as the white matter shown in Fig. 12-e at the discharge rate of 5000X. Further analysis of the composition is in progress.
6. Conclusions 5.2. Effect of the formation water on the above sulfur solvent systems Experiments related to the effect of the formation water on sulfur solubility were studied. Results are shown in Fig. 11 and it can be seen that the solubility of the DMDS solvent system decreased significantly with an increase in formation water. It is more sensitive to temperature than amine solvent system. In addition, research related to compatibility indicate that the amine sulfur solvent system has a good compatibility with formation water, while the DMDS system has the opposite effect. Further study is in progress, including composition analysis of
Propylamine system Diethylene triamine system DMDS system
200 180
Solubility (wt%)
160 140 120 100 80 60
0
5
10
15
20
25
Formation water (wt%) Fig. 11. Effect of formation water on the solubility of solvents.
30
Starting from the sulfur deposition mechanism, some mainstream solvents, organic bases, inorganic bases, phase transfer catalysts and other additives were screened. Three types of sulfur solvents with higher solubility were prepared by complex formulation which expanded our understanding during the process of our study. 1. Some organic and inorganic bases could significantly improve the dissolving ability of the main solvents, like quinoline and sodium hydrosulfide. However, quinoline can inhibit the dissolving ability of DMDS. 2. Phase transfer catalysts (like 18-Crown-6) and additives (such as ferrocene) could significantly improve the sulfur solubility of DMDS system, while they are not suitable for amine solvents. 3. Solvents based on some benzene homologues (such as xylene and chlorobenzene) and selected amine (such as diethylene triamine) solvents would produce a spot of suspected intermediate in the sulfur-dissolving process. The mechanism of sulfur-dissolving of these solvents should be mainly in chemical reactions. 4. Amine sulfur solvent systems have good compatibility with formation water, glycol antifreeze, corrosion inhibitor (JCH2 and FL-7), but the DMDS system was opposite. With the consideration of DMDS's high price and its physical properties, amine sulfur solvent systems are more suitable to be used widely in the development of sour gas reservoirs. 5. Microscopic analysis and comparison indicate that elemental sulfur are dissolved in DMDS and propylamine systems mainly by being encapsulated and forming an emulsion liquid system, but dissolved thoroughly to smaller particles in diethylene triamine system. Though they have the excellent sulfur solubility, large-scale applications would bring enormous cost to industrial
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
Fig. 12. SEM pictures.
production. Research related to circulation utilization of the solvents are very worthy of consideration. Cases of applications in low temperature and corrosion in the process are also worthy to be noticed.
Appendix A. Annexed table
Abbreviations of some chemicals.
Acknowledgments The research is supported by Key Fund Project from Educational Commission of Sichuan Province of China (16CZ0008), Open Fund (PLN1409) and Scientific Project (G201601) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University), The Major Program of the National Natural Science Foundation of China (51490653) and 973 Program (2013CB228004).
Order
Chemical Name
abbreviation
1 2 3 4 5 6 7 8 9 10
dimethyl disulfide 1, 2-dimethoxyethane polyethylene glycol-400 polyethylene glycol-1000 polyethylene glycol-2000 N-Methyl pyrrolidinone N,N-dimethylacetamide N,N-dimethylformamide Dimethylsulfoxide N,N-dimethyl-4-aminopyridine
DMDS DME PEG-400 PEG-1000 PEG-2000 NMP DMAC DMF DMSO DMAP
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
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pipeline in Puguang gas field. Gathering Eng. 31, 75e79. Liu, J.C., Li, Y.C., Zeng, S.P., Xu, C.B., 2008a. Corrosion of sulfur solvent studied in laboratory. Sci. Technol. 35, 237e241. Liu, Y.J., Zeng, S.P., Liu, J.C., Wang, Z.L., Yan, G.Q., 2008b. Laboratory evaluation of sulfur solvent LJ-1. Oil Gas Field Surf. Eng. 27, 30e31. Lyle, F.F., Levhler, S., Brandt, J., Blount, F.E., Snavely, E.S., 1978. Information of steel corrosion in sour gas-well environments containing sulfur and ethylamine. Mater. Perform. 17, 24e31. Mahmoud, M.A., 2014. Effect of elemental-sulfur deposition on the rock petrophysical properties in sour gas reservoir. SPE J. 19, 703e715. Nasr-El-Din, H.A., Al-Humaidan, A.Y., 2001. Iron sulfide scale: formation, removal and prevention, SPE. Reserv. Eval. Eng. 1, 1e13. Schmitt, G., 1991. Effect of elemental sulfur on corrosion in sour gas systems. Corrosion 47, 285e308. Starks, C.M., 1987. Phase-transfer Catalysis: New Chemistry, Catalysts, and Applications. American Chemical Society, Washington. DC. Wilken, G., 1991. Application of alkylnaphthalene absorption oil as a sulfur solvent in sour-gas wells. SPE Prod. Eng. 6, 137e141. Zeng, S.P., Yang, X.W., Zhang, Q.M., Xu, C.B., Liu, J.C., Han, Y.K., Liang, X.Y., Yao, G.M., 2012. Investigating on the prediction model of sulfur deposition in high sour gas-well. Procedia Eng. 29, 4267e4272. Zhang, K.J., Xia, X.X., 2012. Research for novel sulfur solvents. J. Chem. agents 34, 55e57.
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Optimization of effective sulfur solvents for sour gas reservoir Jincheng Mao a, *, Xiaojiang Yang a, Dingli Wang a, Yang Zhang a, Suzhou Luo a, Gregory S. Smith b, Yongming Li a, Jinzhou Zhao a, ** a b
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, PR China Department of Chemistry, University of Cape Town, P. Bag X3, Rondebosch, 7700 Cape Town, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 May 2016 Received in revised form 17 October 2016 Accepted 22 October 2016 Available online 23 October 2016
Sulfur deposition attracts great attention for the exploration of oil and gas and is considered one of the most important hazardous processes in China, and all over the world. Thus, investigating a sulfur solvent is absolutely necessary and highly desirable in the sour gas reservoir development. In recent years, various sulfur solvents were developed and applied in different oilfields. However, they have disadvantages in their practical applications. In this paper, a solution is proposed to solve the problem and improve the sulfur dissolving ability. Three types of sulfur solvents were prepared, all of which have their own characteristics and advantages in different cases and compared with the existing sulfur solvents under the same conditions. The solubility of Dimethyl disulfide(DMDS)-based sulfur solvent system was up to 202.8 wt% at room temperature and 1020.0 wt% at 90 C. Amine solvent systems also achieved high sulfur solubility. The solubility of diethylene triamine-ethanolamine solvent system could reach 79.6 wt% at room temperature and 210.0 wt% in 90 C. It was shown that a more efficient sulfur solvent system can be achieved by remixing with suitable additives. This paper focuses on a preliminary study of optimizing effective sulfur solvents in order to solve the problems caused by sulfur deposition. In the long run, this may revolutionise the process of exploration, transportation and refining of crude oil or natural gas. Microscopic analysis by Scanning Electron Microscope (SEM) was used to facilitate understanding the mechanism of sulfur dissolution in each system and their differences. © 2016 Elsevier B.V. All rights reserved.
Keywords: Sulfur solvent DMDS Diethylene triamine Propylamine Phase transfer catalyst
1. Introduction Sour gas reservoirs are the most important composition of unconventional oil and gas reservoirs, and are widely distributed in China, even all over the world. According to statistical information mentioned in “Sour gas field development technology information publication (edited by China Petroleum and Chemical Corporation)”, more than 300 sour gas fields with industrial value have been discovered all over the world, especially in Russia and Canada, as well as in America, Germany and France. Sour gas is a type of acidic gas which contains 5 ppm H2S, but in China, 60% gas fields contain 20,000e40,000 ppm H2S, some are more than 100,000 ppm. For instance, the proved reserve of Puguang Gas Field is 114.363 billion m3 and the recoverable reserve is 87.832 billion m3, but it contains 1,195,000 ppm. In such gas reservoir
* Corresponding author. ** Corresponding author. E-mail address: [email protected] (J. Mao). http://dx.doi.org/10.1016/j.jngse.2016.10.034 1875-5100/© 2016 Elsevier B.V. All rights reserved.
development processes, accompanied with the gas flow, the elemental sulfur would be easily deposited as the condensate in the form of sulfur, especially when the pressure and temperature were reduced (Zeng et al., 2012; Lyle et al., 1978; Clark et al., 1989; Guo et al., 2015; Hu et al., 2011, 2014a). The reservoir and gathering pipeline can become plugged by such deposition of the sulfur, which seriously affects the production of gas well (Li et al., 2011a). In addition, steel can be seriously corroded by mixtures of sulfur and water. Gathering pipeline and casing would perforate and damage, wells may be shut down or even scraped when corrosion becomes too serious. Worst of all, natural gas leakage caused by it would lead to serious environmental pollution and harmful to human health. It is understood that sulfur usually exists in the form of hydrogen sulfide as a natural gas and hydrogen sulfide is highly toxic. Thus, losses brought by it could not be estimated. For example, a sour gas well blowout occurred in Kaixian county of Chongqing in China on December 23, 2003, injuring more than 93,000 people and killing 243 people. Direct economic losses reached nearly 82 million RMB, while indirect economic losses are
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uncountable. Further to that, hydrogen sulfide leakages occur on a yearly basis in sour gas fields all over the world and kill people through leaks caused by pipeline damage. In order for sour gas reservoirs to be economical, a practical and economical method needs to be developed for exploiting these reservoirs. The problem needs to be solved urgently and it is absolutely necessary to carry out the research to develop sulfur dissolving technology and develop novel, efficient and low-cost sulfur solvent systems to prevent sulfur deposits in pipeline and ensure gathering pipeline work properly (Demirbas et al., 2015; Hilzman and Dennis, 1998; Nasr-El-Din and Al-Humaidan, 2001; Wilken, 1991; Hu et al., 2014b; Mahmoud, 2014; Hassan and Behnam, 2015). Herein, three kinds of sulfur solvents will described for different conditions. 2. Experimental and calculation method
that an aromatic ring can improve the sulfur solubility. It is therefore necessary to study the sulfur solubility of benzene derivatives. 3.1.2. Screening of benzyl solvents The results of the study on sulfur solubility of benzyl solvents are shown in Fig. 2. It can be seen that the sulfur solubility of styrene is higher than the other benzyl solvents. A comparison of the sulfur solubility of toluene and chlorobenzene shows that the CeCl bond can significantly increase the sulfur solubility. However, a comparison of styrene and chlorobenzene indicates that the double bond is more crucial to the sulfur solubility than CeCl bond. Unfortunately, styrene is easily volatilised at high temperatures (Zhang and Xia, 2012). The sulfur solubility of xylene is higher than styrene at 80 C. Considering the volatility and price of benzyl solvents, xylene would be employed in further screening experiments.
2.1. Experimental method A round bottom flask was charged with a given amount of elemental sulfur and solvent. The mixture was stirred with constant speed for 2 h. The undissolved sulfur could be recovered by filtration and dried in an oven at constant temperature (40 C) for 24 h. Then it was weighed for calculating the sulfur solubility. Sulfur dissolving experimental conditions: 25 C, 0.1 MPa. 2.2. Sulfur solubility calculation method It is well known that solubility is defined as the percentage of solute dissolved in the unit mass solvent. It is mathematically described by:
Y¼
M1 M2 100% M
(1)
where Y ¼ solubility of the solvent, M ¼ amount of the solvent, M1 ¼ initial amount of the sublimed sulfur, M2 ¼ final amount of the undissolved sublimed sulfur. 3. Screening experiment 3.1. Screening of main solvents In the experiments of main solvents screened, the amount of each solvent was set to 25 g. A given amount of sulfur was added to the solvent and ensured that it was saturated by sublimed sulfur, then calculating the solubility using the formula above. 3.1.1. Screening of common solvents The sulfur solubility in various common solvents was tested and the corresponding results are shown in Fig. 1. The results show that the solubility of DMDS is significantly higher than the other solvents. The difference of sulfur solubility might be relative to the chemical structures of solvents. DMDS is a stable pale yellow liquid which works as an effective product in the sulfide process because of its high sulfur content. It is also the sulfiding industry's reagent of choice because it offers more sulfur per pound of reagent when compared to its nearest competitor dimethyl sulfide. Initially, it is assumed that the sulfur and ether bond of DMDS may be attributed to its high solubility. However, DME which has an ether structure gave poor results. This is indicative that the sulfur bond will play a more important role to promote the sulfur solubility of the solvent and its dissolution mechanism can be explained as “like dissolves like”. Sulfur reagents usually have bad smell. With the various demands of oilfields, alternative sulfur solvents should be further explored. A comparison of dichloromethane and xylene indicates
3.1.3. Screening of amine solvents Amine solvents have been studied by many researchers. For example, Liu and co-workers revealed that diethylene triamine may be a possible candidate as a sulfur solvent (Liu et al., 2008a, 2008b). To acquire more efficient soluble systems, it is necessary to perform extensive research on amine solvents. Thus, thirteen amine solvents were chosen to test their sulfur solubilities, as shown in Fig. 3. In a different approach, the process of reacting anmine solvents with sulfur results in the release much heat and thus, an increase in the temperature of the solution, will lead to higher sulfur solubility. Notably, the sulfur solubility of diethylene triamine or propylamine is significantly higher than DMDS at room temperature. By raising the temperature, the dissolution rate of triethylene tetramine became faster than diethylene triamine. In 2014, Guo and coworkers found that the sulfur dissolution rate of triethylene tetramine was 24.65 g/min/L and diethylene triamine was only 22.25 g/ min/L (Guo, 2014). However, the sulfur solubility of diethylene triamine was higher than triethylene tetramine albeit at higher temperatures or room temperature. Therefore, it is incorrect to generally conclude that more amine groups in molecules can afford higher sulfur solubility. A comparison of ethanolamine, diethanolamine and triethanolamine indicates that a hydroxy group is unfavorable for the sulfur solubility. It can be seen that the sulfur solubilities of diethylene triamine and propylamine are both beyond 28 wt%. However, we found that during the course of filtration, the solution of diethylene triamine was too sticky to handle. In addition, the boiling point of propylamine is very low (about 48 C) and thus it is recommended to be used at room temperature. In order to reduce the viscosity of diethylene triamine sulfur solution, mixed solvent experiments were designed. Other solvents were set to 50 wt% of diethylene triamine and the relative results are shown in the Table 1. In view of the high price of DMDS and high volatility of propylamine, ethanolamine will be most suitable to reduce the viscosity of diethylene triamine sulfur solution and the optimal proportion was found to be 2:1 (diethylene triamine: ethanolamine). 3.1.4. Comparative analysis It can be seen from the above screening experiments that DMDS, diethylene triamine and propylamine are the most promising candidates as the efficient sulfur solvents. Besides the difference of solubility, some other phenomena were noticed during the course of experiments. The appearance of most of filtering sulfur is similar to the sublimed sulfur and sometimes the color becomes light. However, for the benzyl solvents, especially for benzene and chlorobenzene, some black particles were found in the filtering
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
Fig. 1. The solubility of common solvents.
Fig. 2. The sulfur solubility of benzyl solvents.
Fig. 3. The solubility of amine solvents.
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471 Table 1 Cosolvent screening experiments. Cosolvent
Initial sulfur (g)
Undissolved sulfur (g)
Filtering time (min)
Phenomenon
DMDS propylamine ethanolamine ethylenediamine triethylenetetramine xylene methyamine diethylene Driethylenediamine isopropylamine
7 7 7 7 7 7 7 7 7 7
0 0 0 0.71 12.02 15.04 15.35 16.48 19.71 19.84
10 15 16 14 20 20 20 20 20 20
turn turn turn turn turn turn turn turn turn turn
black black black black, layered black black, layered black black black black, layered
cakes as shown in Figs. 4e5. It is noteworthy that for the amine solvents, the color of the system significantly changed to brown after dissolving the sulfur, as shown in Fig. 6. It can be assumed from this special phenomena that black particles and dark viscous materials may be caused from their chemical reactions between them, to form some intermediates or complexes. Further determinations based on modern physical machines are underway in our laboratory.
3.2. Screening of various additives
Fig. 4. Filtering products of xylene sulfur solution.
Fig. 5. Filtering products chlorobenzene sulfur solution.
SULFA-HITECH which is an efficient sulfur solvent was prepared by Pennwalt of America in 1988 by adding a small amount of inorganic base (sodium hydrosulfide) and DMF to DMDS. However, the organic base-amine solvents were found efficient as sulfur solvents in the above experiment (Liu et al., 2008b). Therefore, the screening of organic and inorganic bases is extremely necessary. Xylene was used as the main solvent for the screening experiments in view of its low price. Results of the experiments are shown in Table 2. It can be seen that quinoline (organic bases) and sodium hydrosulfide (the inorganic bases) can significantly improve the sulfur solubility of xylene. A phase transfer catalyst (PTC) is a type of catalyst which is helpful to transfer reactants from one phase to another phase, making it easier to perform the reaction in a heterogeneous system (Starks, 1987). In principle, it is most likely improve the sulfur dissolving ability of sulfur solvents. Thus, PTCs were screened in a mixed solution of xylene and quinoline. Finally, it was found that 18-crown-6 was the only catalyst which can improve sulfur solubility of the solution. Detailed data of experiments are listed in Table 3. Furthermore, the efficient additive could enhance intermolecular forces of S8 by a large p bond, forming sandwich structures and thus improving the sulfur solubility of the system. Ferrocene is one such kind of sandwich complex which has an aromatic property, high boiling point, stable physical and chemical properties. The results of the experiment showed that ferrocene is a better phase transfer catalyst (18-crown-6) on the aspect of improving solubility of sulfur solvents. Therefore, it would make sense to mix these together with 18-crown-6 and other solvents, in an effort to achieve more efficient sulfur solvent systems.
4. The formation of formula
Fig. 6. Filtering products of diethylene triamine sulfur solution.
The formula of a sulfur solvent system depends on not only the suitable additives, but also on a certain ratio. The following experiments detail the various components of the system.
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471 Table 2 Screening experiments of various bases. Organic bases
Solubility (%)
Inorganic bases
Solubility (%)
quinoline DMAP pyridine hydroxyquinoline Propylamine triethylenediamine ethanolamine indole pyrazole N,N-dimethylaniline triethylenetetramine triethylamine blank piperidine 2-amino-6-chlorobenzothiazole diethylamine melamine diethylene triamine
3.36 3.32 3.24 3.16 3.16 3.04 3.00 2.92 2.80 2.76 2.76 2.72 2.72 2.64 2.60 2.48 2.44 2.00
sodium hydrosulfide sodium sulfide sodium sulfate sodium bisulfite sodium sulfite sodium thiosulfate sodium acetate sodium salicylate sodium bisulfate sodium bicarbonate blank disodium hydrogen phosphate sodium hydroxide sodium dihydrogen phosphate sodium persulfate sodium formate sodium carbonate
3.56 3.36 3.28 3.24 3.04 3.00 2.96 2.96 2.88 2.76 2.72 2.64 2.60 2.52 2.48 2.20 2.04
Table 3 Screening experiments of various phase transfer catalysts. PTC
Solubility (%)
Special phenomenon
18-Crown-6 blank cetyltrimethylammonium chloride Tetrabutylammonium chloride Tetramethylammonium chloride tetramethylammonium silicate Tetrabutylammonium acetate Tetramethylammonium Iodide PEG-400 dodecyl trimethyl ammonium bromides cetyltrimethylammonium bromide PEG-1000 PEG-2000 tetrabutylammonium bromide tetrabutylammonium iodide
3.52 3.36 3.16 3.08 3.04 3.00 2.88 2.88 2.72 2.36 2.32 2.32 2.24 2.20 2.00
nothing nothing nothing nothing nothing nothing nothing white precipitation black phase and points structure nothing black massive and flake structure white precipitation white precipitation nothing nothing
4.1. DMDS solvent system 4.1.1. Screening of auxiliaries It was found that auxiliaries can significantly improve sulfur solubility of a DMDS sulfur solvent by studying existing DMDS systems. Selecting a suitable auxiliary is extremely necessary to prepare an efficient sulfur solvent. In an auxiliary screening experiment, DMDS was set to be 5.0 g, sodium hydrosulfide was 0.5 wt% and the auxiliary was 5.0 wt%. Information from the results shown in the Fig. 7, indicate that DMSO is the best and it is slightly better than DMF used under the same conditions. 4.1.2. The formation of formula To our surprise, we found that quinoline would inhibit the solubility of a DMDS system. Thus, the preliminary DMDS system formula will consist of DMDS, DMSO and sodium hydrosulfide. However, the ratio of the composition in the system would greatly affect solubility of the sulfur solvent. The ratio of each reagent was determined by experiment: DMDS, DMSO (5.0 wt%) and sodium hydrosulfide (0.5 wt%). Results of the experiments are shown in Table 4. Based on the result of the above basic screening experiments, the ratio of the phase transfer catalyst and additive was studied. Results of the experiments are shown in Table 5 and the final formula of DMDS sulfur solvent system were DMDS, DMSO (5.0 wt%), sodium hydrosulfide (0.5 wt%), 18-crown-6 (1.0 wt%) and ferrocene
Fig. 7. Auxiliary solvents for DMDS system.
Table 4 Result of preliminary complex formulation experiment. DMSO (%)
5.00
5.00
2.50
2.50
Sodium hydrosulfide (%) Solubility (%)
0.50 168.2
1.00 154.0
0.50 150.8
1.00 135.2
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
(1.0 wt%). It can be seen from the table that the sulfur solubility of the system could reach 202.8 wt% at room temperature.
Table 5 Effect of catalysts on the solubility of DMDS solvent system. catalyst
Solubility (wt%)
18-crown-6 (wt%)
Ferrocene (wt%)
1.0 0.0 1.0 0.0
1.0 1.0 0.0 0.0
4.2. Amine solvents system 202.8 170.6 169.4 168.2
Table 6 Result of remixing with alkaline system. alkaline
Solubility (wt%)
quinoline sodium hydrosulfide
Propylamine
Diethylene triamine
65.4 68.2
63.8 65.2
75
Diethylene triamine Propylamine
70
Solubility (wt%)
65 60 55 50 45 40
5. Performance evaluation
0
1
2
3
4 5.1. Effect of temperature on sulfur solvent system achieved above
Ratio of sodium hydrosulfide (wt%) Fig. 8. Ratio determination of amount NaHS.
85
Propylamine Diethylene triamine
80 Solubility (wt%)
Propylene and diethylene triamine-ethanolamine were found to be efficient sulfur solvents in the above screening experiments. Thus, remixing experiments of amine solvents were investigated. The results listed in Table 6 indicate that quinoline and sodium hydrosulfide can significantly improve the solubility of amine solvents. In the experiment concerning formula formation of amine solvents and sodium hydrosulfide, it was found that the sulfur solubility was highest when sodium hydrosulfide accounts for 1.0 wt% of amine (propylamine and diethylene triamine) solvents. The results of the experiment are shown in Fig. 8. Based on the above research, NaHS was set to be 1.0 wt% of amine solvents, and the amount of quinoline was screened. Results are shown in Fig. 9 and it can be seen that the most suitable amount of quinoline is 2.0 wt% of the amine solvents. Considering the accelerated role of ferrocene and 18-crown-6 in improving the sulfur solubility of DMDS system, their effects on amine solvents were investigated carefully. In the experiments, amine solvents were set to be 5.0 g, sodium hydrosulfide was 1.0 wt% and quinoline was 2.0 wt%. Results are shown in Table 7. It can be observed that ferrocene and 18-crown-6 could not improve the solubility of the amine solvents, but inhibit the dissolving ability. Finally, the ratio of the amine sulfur solvent systems were determined to be as follows: propylamine, sodium hydrosulfide (1.0 wt%), quinoline (2.0 wt%), diethylene triamine-ethanolamine, sodium hydrosulfide (1.0 wt %), and quinoline (2.0 wt%). The solubility of propylamine system reached 80.4 wt% and the diethylene triamine system reached 79.6 wt% at room temperature.
75
70
Considering the volatility of propylamine, only the effects of temperature on DMDS and diethyllene triamine systems were investigated. Based on the optimal ratio of the reagents, sulfur dissolution experiments were analyzed at 25, 80 and 90 C. Results of the experiments are shown in Fig. 10. Information gleaned from the figure indicates that the solubility of the sulfur solvent systems increases with an increase in temperature. Notably, an increase in the amount of the DMDS system was most significant. The sulfur solubility of DMDS reached 1020 wt% at 90 C, which is the best result thus far. Upon increasing temperature, the reaction constant of sulfur dissolution is increased, which enhances the sulfur dissolving ability (Schmitt, 1991). In addition, polysulfide which is generated from DMDS and sulfur could further dissolve sulfur. Comparatively, the
Table 7 Screening important additives. Additives
65
0
1
2
3
Ratio of quinoline (wt%) Fig. 9. Ratio determination of quinoline.
4
Solubility (wt%)
18-crown-6 (wt%)
Ferrocene (wt%)
Propylamine
Diethylene triamine
0.0 1.0 0.0 1.0
0.0 1.0 1.0 0.0
80.4 77.6 64.4 63.8
79.6 75.4 63.2 62.8
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
the solvents, and the mechanism of dissolution.
5.3. Microscopic analysis and comparison
Fig. 10. Effect of temperature on the solubility of solvents.
temperature does not show such a dramatic influence on the solubility of the amine solvent system (210 wt% in 90 C). To this end, the solubility has been improved because of the raised temperature. The relative mechanism is underway in our laboratory.
Microscopic analysis aimed at facilitating the understanding of the mechanism of sulfur dissolution in each system and their differences, is as shown in Fig. 12. Compared with elemental sulfur, it was found that residual particles of the DMDS system had a low dispersion and large agglomerates due to solvent invasion. Elemental sulfur was dissolved in the DMDS system by being encapsulated and forming an emulsion liquid system. The residual of elemental sulfur in propylamine system could also be examined. However, these particles were more regular than the particles in the DMDS system and their shapes look like monocline crystal of sulfur. It is estimated that solid sulfur was composed of rhombic sulfur and monocline crystals of sulfur. Moreover, rhombic sulfur is recrystallized and thus dissolved more easily than monocline crystal of sulfur. The propylamine system was preferential to dissolve rhombic sulfur of solid sulfur. The residue of the diethylene triamine system was a quite different sticky material, a new resultant and we could not find solid particles at the same discharge rate. Elemental sulfur may be dissolved to smaller particles as the white matter shown in Fig. 12-e at the discharge rate of 5000X. Further analysis of the composition is in progress.
6. Conclusions 5.2. Effect of the formation water on the above sulfur solvent systems Experiments related to the effect of the formation water on sulfur solubility were studied. Results are shown in Fig. 11 and it can be seen that the solubility of the DMDS solvent system decreased significantly with an increase in formation water. It is more sensitive to temperature than amine solvent system. In addition, research related to compatibility indicate that the amine sulfur solvent system has a good compatibility with formation water, while the DMDS system has the opposite effect. Further study is in progress, including composition analysis of
Propylamine system Diethylene triamine system DMDS system
200 180
Solubility (wt%)
160 140 120 100 80 60
0
5
10
15
20
25
Formation water (wt%) Fig. 11. Effect of formation water on the solubility of solvents.
30
Starting from the sulfur deposition mechanism, some mainstream solvents, organic bases, inorganic bases, phase transfer catalysts and other additives were screened. Three types of sulfur solvents with higher solubility were prepared by complex formulation which expanded our understanding during the process of our study. 1. Some organic and inorganic bases could significantly improve the dissolving ability of the main solvents, like quinoline and sodium hydrosulfide. However, quinoline can inhibit the dissolving ability of DMDS. 2. Phase transfer catalysts (like 18-Crown-6) and additives (such as ferrocene) could significantly improve the sulfur solubility of DMDS system, while they are not suitable for amine solvents. 3. Solvents based on some benzene homologues (such as xylene and chlorobenzene) and selected amine (such as diethylene triamine) solvents would produce a spot of suspected intermediate in the sulfur-dissolving process. The mechanism of sulfur-dissolving of these solvents should be mainly in chemical reactions. 4. Amine sulfur solvent systems have good compatibility with formation water, glycol antifreeze, corrosion inhibitor (JCH2 and FL-7), but the DMDS system was opposite. With the consideration of DMDS's high price and its physical properties, amine sulfur solvent systems are more suitable to be used widely in the development of sour gas reservoirs. 5. Microscopic analysis and comparison indicate that elemental sulfur are dissolved in DMDS and propylamine systems mainly by being encapsulated and forming an emulsion liquid system, but dissolved thoroughly to smaller particles in diethylene triamine system. Though they have the excellent sulfur solubility, large-scale applications would bring enormous cost to industrial
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
Fig. 12. SEM pictures.
production. Research related to circulation utilization of the solvents are very worthy of consideration. Cases of applications in low temperature and corrosion in the process are also worthy to be noticed.
Appendix A. Annexed table
Abbreviations of some chemicals.
Acknowledgments The research is supported by Key Fund Project from Educational Commission of Sichuan Province of China (16CZ0008), Open Fund (PLN1409) and Scientific Project (G201601) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University), The Major Program of the National Natural Science Foundation of China (51490653) and 973 Program (2013CB228004).
Order
Chemical Name
abbreviation
1 2 3 4 5 6 7 8 9 10
dimethyl disulfide 1, 2-dimethoxyethane polyethylene glycol-400 polyethylene glycol-1000 polyethylene glycol-2000 N-Methyl pyrrolidinone N,N-dimethylacetamide N,N-dimethylformamide Dimethylsulfoxide N,N-dimethyl-4-aminopyridine
DMDS DME PEG-400 PEG-1000 PEG-2000 NMP DMAC DMF DMSO DMAP
J. Mao et al. / Journal of Natural Gas Science and Engineering 36 (2016) 463e471
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