- Email: [email protected]
Laboratory experiment and field application of high pressure and high quality steam flooding
Journal Pre-proof Laboratory experiment and field application of high pressure and high quality steam flooding Yan Zhao PII:
S0920-4105(20)30111-X
DOI:
https://doi.org/10.1016/j.petrol.2020.107016
Reference:
PETROL 107016
To appear in:
Journal of Petroleum Science and Engineering
Received Date: 24 May 2019 Revised Date:
30 January 2020
Accepted Date: 1 February 2020
Please cite this article as: Zhao, Y., Laboratory experiment and field application of high pressure and high quality steam flooding, Journal of Petroleum Science and Engineering (2020), doi: https:// doi.org/10.1016/j.petrol.2020.107016. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
2
Laboratory experiment and field application of high pressure and high quality steam flooding
3
YanZhao
4
(Shengli College, China University of Petroleum, Dongying City, Shandong Province, 257000, China)
5
Corresponding author. Shengli College, China University of Petroleum, Dongying City, Shandong Province,
1
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Steam flooding is an effective way to improve oil recovery after steam huff and puff for heavy oil reservoirs. The typical screening criteria for steam flooding requires reservoir pressure to be less than 5 MPa, the steam quality of conventional steam flooding in bottom hole is about 30%, heavy oil reservoir in Shengli Oilfield with character of deep burial depth, active edge and bottom water and high formation pressure (7-8 MPa), the increase of oil recovery using conventional steam flooding is not obvious, Therefore, the formation and development of steam chamber during steam flooding are studied by indoor physical simulation experiments, the feasibility of high-quality steam flooding under high pressure is analyzed. The experimental results show that the quality of steam injection has obvious influence on the expansion of steam chamber. As the steam quality increases under high pressure, the specific volume of underground steam increases, the formation time of steam chamber is shortened, the expansion distance of steam chamber increases, the effective steam flooding time is prolonged, and recovery rate improves obviously . Field tests of high-quality steam flooding under high presure were carried out in Gudao Zhongerbei heavy oil reservoir of Shengli Oilfield, the result shows that the bottom-hole steam quality of steam injection wells is 50 % and above (20% higher than conventional steam flooding), the steam chamber was effectively expanded and the performance of producing rate for production wells improves obviously. The recovery rate of the test area reached 52.1%, which was 16.8% higher than that of steam huff and puff. High-quality steam flooding technology was an effective way to improve the recovery rate of high-pressure heavy oil reservoirs.
29
Key words: heavy oil; steam flooding; pressure; steam quality; recovery factor
30 31 32 33 34 35 36 37 38 39 40 41 42 43
Introduction
257000, China.E-mail address: [email protected] (YanZhao).
Abstract
Steam flooding is an effective way to further increase oil recovery rate after huff and puff in heavy oil reservoirs [1-4]. The increase rate of oil recovery by successful steam flooding is very high all ove the world. According to the conventional steam flooding screening criteria, for heavy oil reservoirs with reservoir pressure higher than 5 MPa, it is not suitable to use steam flooding to improve oil recovery rate[5-7]. Shengli Oilfield has abundant heavy oil resources. By 2018, 557 million tons of heavy oil geological reserves have been produced in Shengli Oilfield. More than 90% of the productions is deep heavy oil with buried depth of 1000 1400 meters, and most of them have edge and bottom water [8-9]. Therefore, the pressure drop is slow using huff and puff method. It is very difficult for the pressure of heavy oil reserves with reservoir pressure to be reduced to 5 MPa. The field practice of conventional steam flooding (about 30% steam injection quality) has shown that when the reservoir pressure increase, the recovery factor of steam flooding decreases obviously [10-11]. In recent years, high-quality steam injection technology has made great progress [12-13]. Bottom-hole steam quality of Shengli Oilfield deep heavy oil reservoir has
44 45 46 47 48
increased from 30% to 50%. For this reason, physical simulation experiments of high- quality steam flooding under 7MPa condition have been carried out. These experiments are very helpful to both monitor the development of steam chamber during steam flooding, and study the feasibility of high- quality steam flooding under high pressure. This provides an effective way to increase oil recovery rate of high-pressure heavy oil reservoir.
49
1. Experimental design
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
1.1. Experimental device This experiment adopts a self-developed two-dimensional proportional high-pressure steam thermal recovery physical simulation device (Fig. 1). The simulation device consists of injection system, model body, output system, measurement and control system. The model body is a vertical two-dimensional high-pressure model, which can withstand 10 MPa pressure and 300 temperature. It can simulate the profile of vertical heterogeneity between injection and production wells. The injection system mainly composes of high-pressure constant-speed pump, steam generator, intermediate container, pipe and valve components, which can generate steam for injection with different quality. The main output system is the oil-water metering device, which completes the separation and measurement of the model produced liquid. The measurement and control system include pressure monitoring device and temperature acquisition device. The pressure monitoring device monitors the pressure at the inlet and outlet, and reflects the variation of model pressure in real time. The temperature acquisition device collects the temperature change at the temperature measuring point in the model in real time through thermocouples at each layer, and stores, processes and displays the temperature field map on computer.
66 67 68 69 70 71 72 73 74 75 76 77 78 79
Fig.1
Two-dimension physical model of steam recovery
1.2. Physical model According to the similarity criterion of steam flooding physical simulation, using Ng5 heavy oil reservoir in Zhongerbei of Gudao Oilfield as the prototype and combining with reservoir geological development parameters, a two-dimensional physical simulation model of vertical heterogeneity is established to simulate the cross-well profile of one injection and one production well. The model is 700 mm wide and 90 mm high. It has seven simulated layers in vertical direction. There are 17 thermocouples in each layer and 119 thermocouples in total (Table 1). Any temperature profile in the reservoir can be obtained by interpolation. The steam chamber distribution and the steam front in the vertical direction can be judged by the temperature profile. The tubing string is made of stainless-steel pipe with a diameter of 6 mm and is sliced at the reservoir to simulate the perforation section of field wells. The oil used in the experiment is the crude oil from the Zhongerbei formation in Gudao. The surface (50 ) dead oil viscosity is 3783
80 81 82 83
mPa·s, the surface dead oil density is 0.9764 g/cm3, the initial reservoir temperature is 65 C, the reservoir model pressure is 7 MPa, the production time is 25.7 min, and the steam injection speed is 25 mL/min. Table1
Physical property parameters of each layer thickness cm
permeability 10-3μm2
K1layer
1.59
1594
K2layer
1.33
1606
interlayer
1.49
K3layer
0.95
1495
K4layer
1.18
1477
interlayer
1.07
K5layer
1.39
Total
9.00
Layering/lamination
1381
84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106
1.3. Experimental scheme and steps Three experimental schemes have been designed. Scheme 1 injects steam with 10% steam quality, scheme 2 injects steam with 30% steam quality and scheme 3 injects steam with 50% steam quality. In order to make comparation, temperature field changes during steam flooding were monitored by temperature sensors, oil-water separation and quantitative analysis were carried out for the model produced liquid, production indexes of different schemes were determined, and the effects of steam injection quality on the effect of steam flooding development and steam chamber sweeping pattern were studied. The experimental include the following steps: model loading. Firstly, load the model with different particle sizes sand, and the air permeability is tested by single tube model to make the air permeability equal to the model permeability. The using sand is the fractured sand with uniform particle size after acid treatment. After filling the model by water injection sedimentation method, the water leakage test is carried out. The test pressure, 9 MPa, not reducing in 1h is regarded as qualified. Then the water in the model will be released. Vacuumized the model. And then be saturated with distilled water. The pore volume and porosity are measured by T-type. Model initialization. The oil saturation and irreducible water saturation of each layer are calculated by injecting the experimental oil into the model at a constant low speed until no water is produced at the outlet. The temperature and pressure of the model are adjusted to keep it stable at the simulated temperature and pressure for 12 hours. Steam flooding simulation under different experimental schemes. The steam injection rate is 25 mL/min. The inlet and outlet pressure and the temperature field of each layer are recorded regularly, and the oil production, water production and injection quantity are measured.
107
2.Experimental results and analysis
108 109 110 111 112 113 114
2.1. Variation of steam chamber It can be seen from the variation of longitudinal temperature field of scheme 1, scheme 2 and scheme 3 models with injection volume (fig. 2-4) that the steam quality of scheme 1 is 10%. Most of the injected steam is hot water, and the amount of dry steam is small. The latent heat of vaporization is low. The time efficiency of injecting heat is low. The temperature field expands slowly. When the amount of injected steam (water equivalent) reaches 3.0 PV, steam chamber begins to form in the upper permeable layer. With the continuous injection of steam, the steam
115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
chamber gradually expands forward. The steam drive ends when the steam injection amount (water equivalent) reaches 4.6 PV,. From the direction of the injection well to the production well, several different temperature zones are formed, namely, the steam chamber near the injection well, the condensation hot water zone behind the steam chamber, and the original temperature zone near the production well. The expansion distance of the steam chamber is small. Only about 1/10 of the well spacing, most of the models are hot water zones, accounts for nearly 6/10 of the well spacing. There is no steam chamber in the middle and lower permeable layers. It shows that, under the condition of 7 MPa pressure and 10% steam injection quality, the underground flooding mode is basically hot water flooding. The steam injection quality of scheme 2 is 30%, the expansion speed of temperature field is accelerated. When the injection volume reaches 2.2 PV, the steam chamber begins to form in the upper two permeable layers. The steam drive ends when the injection volume (water equivalent) reaches 5.5 PV,. The expansion distance of the steam chamber is larger than that of scheme 1, accounting for nearly one sixth of the well spacing, but the development of the steam chamber is still unsatisfactory. Scheme 3’s steam injection quality is 50%, and when the injection volume reaches 1.3 PV, the steam chamber begins to form in all upper three permeable layers. When steam injection volume (water equivalent) reaches 6.5 PV, steam flooding ends. The expansion distance of steam chamber increases obviously, approaching 1/2 of well spacing, reservoir temperature rises obviously, the expansion distance of steam chamber in upper permeable layer is larger, showing the characteristics of steam overlap. Compared with the steam chamber formation time, the steam flooding time and the expansion distance of the steam chamber at the end of steam flooding of scheme 1, scheme 2 and scheme 3, it can be found that with the increase of steam injection quality, the formation time of steam chamber decrease, the steam flooding time becomes longer, and the expansion distance of steam cavity becomes larger at the end of steam flooding. The reason is that in the process of steam flooding, when the reservoir is heated to the saturation temperature of the steam, the steam chamber starts to form. During this period, a large amount of steam is needed to condense into hot water, release heat to heat crude oil and rock. High quality of steam injection can take high latent heat of steam vaporization resulting in high time efficiency of injecting heat, shorter time of forming steam chamber and faster expansion speed. At the same time, heating and viscosity reduction are the main factors of steam flooding. The higher the quality of steam injection, the higher the enthalpy of heat carried, the more fully heated of the crude oil, the better the flow ability of the crude oil, the lower the mobility ratio of water to oil, the weaker the steam coning, and the more balanced of the steam advancing, so the steam flooding time becomes longer.
150 151
Fig.2
the temperature field in experimental scheme 1
Fig.3
the temperature field in experimental scheme 2
152 153
154
155 156 157 158 159 160 161 162 163 164 165 166 167
Fig.4
the temperature field in experimental scheme 3
2.2. Development effect By comparing the recovery percentage of three experimental schemes with the variation of injection pore volume multiple (Fig. 5), it can be seen that the ultimate recovery percentage of scheme 3 is 59.9%, the steam flooding time is the longest, the ultimate recovery percent of scheme 2 is 51.9%, the ultimate recovery percentage of scheme 1 is 45.6%. The steam injection quality increases from 10% to 50% under 7 MPa reservoir pressure, while the recovery percentage of steam flooding stage increases by 14.3%. The steam injection quality has a significant impact on the recovery of steam flooding. Increasing the steam injection quality can effectively improve the development effect of deep heavy oil steam flooding. The main reason is that when the steam injection quality is improved, the expansion distance of the steam chamber becomes larger, and the oil displacement efficiency of the steam chamber is obviously higher than that of the hot water zone at the same temperature, so the steam displacement recovery degree is obviously improved.
168 169
Fig.5
Change of recovery percentage in experimental scheme 1,2,3
170
3. Pilot test
171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187
3.1. Basic information of the test area The test area is located in the main part of Zhongerbei Ng5 heavy oil unit in Gudao, Shengli Oilfield. Four large well spacing groups with 141×200m and four small well spacing groups with 100×141m are deployed. The oil-bearing area is 0.51 km2 and the OOIP is 122×104t. The target stratum in the test area is gentle with buried depth of 1286-1316m and some certain edge water in the north. The effective thickness is 10.2m, the porosity is 31%, the average air permeability is 2300×10-3µm2, and the crude oil viscosity is 546.3 mPa·s under reservoir condition. It belongs to the fluvial facies deposited unconsolidated sandstone reservoir with high porosity and high permeability. Steam stimulation recovery development was started in October 1992 in the test area. Displacement characteristic curve method and numerical simulation method was used in this area, the steam stimulation recovery rates of large and small well spacing groups were 35.2% and 35.5% respectively. In October 2010, small well spacing groups changed to high quality steam flooding, by then the formation pressure ranged from 7 MPa to 8 MPa, the recovery percentage was 31.4% and the water cut was 89.0%. In March 2011, large well spacing groups turned to the same recovery method, and the formation pressure was 7 8 MPa, the recovery percentage was 33.5% and the water cut was 91.8%.
188 189 190 191 192 193 194 195 196 197
3.2. Steam injection status High quality steam injection boiler is used in this area. The field application shows that the steam quality at the outlet of the boiler can approach 99%. In order to reduce wellbore heat loss, high vacuum insulated tubing is used in wellbore steam injection string, and heat insulation bushing and heat insulation compensator are used to insulate hot spots of steam injection string. The apparent thermal conductivity coefficient of steam injection tubing string is only 0.0068W/(m· ). After adopting the above measures to improve bottom-hole steam quality, 8 steam injection wells were sampled and tested for bottom-hole steam quality under the 5 t/h steam injection speed. The actual bottom-hole steam quality can reach more than 50% and meet the requirements of high- quality steam flooding.
198 199 200 201 202 203 204 205 206 207 208 209
3.3. Test effect From the production curve of the test area, the daily oil production rate of 17 wells in four small well spacing groups increased from 20.2 t/d to 101 t/d, the total water cut decreased from 89% to the lowest 74.6%, the daily oil production of 21 wells in the four large well spacing groups increased from 61 t/d to 113 t/d, and the total water cut decreased from 89.7% to the lowest 85.5%. Up to June 2016, the daily oil production of eight well groups in the test area was 108 t/d, the total water cut was 90.4%, the cumulative oil production was 23.6×104 t, the recovery percentage was 52.1%, and the recovery factor increased by 16.8%. The cumulative oil production of four small well spacing groups was 10.3 ×104t, the stage oil-gas ratio was 0.16t/t, the recovery percent was 55.8%, and the recovery rate has been increased by 20.3%; the cumulative oil production of four large well spacing groups was 13.3 ×104t, the stage oil-gas ratio is 0.15t/t, the recovery percentage was 50.0%, and the recovery rate has been increased by 14.8%.
210
211 212 213 214 215 216 217 218
Fig.6
Production curve of pilot test
In October 2014, a sealed coring well 26XJ532 was drilled on the main stream line, 77.7 m away from the steam injection well in the 26-N533 small well spacing group. The average remaining oil saturation in core analysis was 19.8%, and the inter-well oil saturation was greatly reduced. The oil displacement effect of upper reservoir was better, and the remaining oil saturation in core analysis was only 15.7% (fig.7). After oil-water saturation correction, the average remaining oil saturation is 27.7%, the average oil displacement efficiency is 62.4%, and the upper reservoir oil displacement efficiency is 70.5%.
219 220
Fig.7
Remaining oil saturation of sealed coring well 26XJ532
221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245
4. Conclusion (1) Laboratory experiment results show that steam quality has a significant effect on the expansion of steam chamber during steam flooding. Under the condition of 7MPa, the formation time of steam chamber is shortened, the total steam flooding time is longer, and the expansion distance of steam chamber is larger at the end of steam flooding. At the same time, under the condition of 7MPa, as the steam quality increases, the steam flooding recovery is greatly improved. (2) High pressure and high steam quality flooding has achieved good results in Gudao Zhongerbei heavy oil unit of Shengli Oilfield. The steam flooding recovery rate is 52.1% at 7MPa reservoir pressure and 50% steam quality, which is increased by 16.8%. (3) Laboratory and field tests show that high dryness quality flooding technology is feasible, and it is an effective method to improve the recovery of high-pressure heavy oil reservoirs.
Acknowledgements This work was sponsored by National Science and Technology Major Project of China (2016ZX05011-003), Sinopec scientific research project (P17003).
References [1] Yue Qingshan,1998. Thermal technology for Steam Injection in Heavy Oil Reservoirs. Beijing: Petroleum Industrial Press, 26-147. [2] Liu Wenzhang,1997. Thermal engineering for heavy oil reservoirs. Beijing: Petroleum Industrial Press, 348-393. [3] Shen Pingping,2005. Thermal technology for EOR. Beijing: Petroleum Industrial Press, 23-56. [4] Yang Zhanwei, Zhao Qishuang, Chen Gang, 2012. Optimization of development mothods for heavy oil
246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266
reservoir of KS Oilfield. Fault-Block Oil
Gas Field, 19(1),21-24.
[5] Zhang Yitang, Li Xiuluan, Zhang Xia,2008. Four fundamental principles for design and follow-up of steam flooding in heavy oil reservoirs. Oil Drilling & Production Technology, 35(6),715-719 [6] Yue Qingshan, Li Pingke,1997. Effect of reservoir pressure on development result of steam drive. Special Oil & Gas Reservoirs, 4(4), 15-18 [7] Su Yuliang, Gao Haitao,2009. Influencing factors of thermal efficiency during heavy oil steam drive. Fault-Block Oil
Gas Field, 16(2), 72-74.
[8] Yang Yuanliang,2011. Pilot test of steam flooding in super heavy oil reservoirs in Shan 56 area. Journal of Oil and Gas Technology, 33(1), 142-144. [9] Tao Lei, Li Zhaomin, Bi Yiquan, Li Binfei,2010. Multi-combination exploiting technique of ultra-heavy oil reservoirs with deep and thin layers in Shengli oilfield. Petroleum Exploration and Development, 37(6), 732-736. [10] Cao Yanbin, Liu Dongqing, Wang Shantang, 2014. Three-dimensional physical simulation and application of chemistry assistant steam flooding on middle and deep heavy oil reservoir. Acta Petroleum SINICA, 35(4), 739-744. [11] Song Yang,2013. Optimization design of steam flooding for horizontal well in thin heavy oil reservoir. Fault-Block Oil
Gas Field, 20(2), 239-241.
[12] Shi Qinfang,2013. Special(Micro)Overheat Steam Generator Research and Application in Oilfield. Journal of Petrochemical Universities, 26(2), 63-67 [13] Shi Qinfang,2013. Design of the water treatment system for high quality steam generator. Automation & Instrumentation, 3(2), 65-66
Highlight (1) Laboratory experiments show that steam quality has a significant effect on the expansion of steam chamber during steam flooding. Under the condition of 7MPa, the formation time of steam chamber is shortened, the total steam flooding time is longer, and the expansion distance of steam chamber is larger at the end of steam flooding. At the same time, under the condition of 7MPa, as the steam quality increases, the steam flooding recovery is dramatically improved. (2) High pressure and high steam quality flooding has achieved good results in Gudao Zhongerbei heavy oil unit in Shengli Oilfield. The steam flooding recovery rate is 52.1% at 7MPa reservoir pressure and 50% steam quality, which is increased by 16.8%. (3) Laboratory and field tests show that high dryness quality steam flooding technology is feasible, and it is an effective method to improve the recovery of high-pressure heavy oil reservoirs.
S0920-4105(20)30111-X
DOI:
https://doi.org/10.1016/j.petrol.2020.107016
Reference:
PETROL 107016
To appear in:
Journal of Petroleum Science and Engineering
Received Date: 24 May 2019 Revised Date:
30 January 2020
Accepted Date: 1 February 2020
Please cite this article as: Zhao, Y., Laboratory experiment and field application of high pressure and high quality steam flooding, Journal of Petroleum Science and Engineering (2020), doi: https:// doi.org/10.1016/j.petrol.2020.107016. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
2
Laboratory experiment and field application of high pressure and high quality steam flooding
3
YanZhao
4
(Shengli College, China University of Petroleum, Dongying City, Shandong Province, 257000, China)
5
Corresponding author. Shengli College, China University of Petroleum, Dongying City, Shandong Province,
1
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Steam flooding is an effective way to improve oil recovery after steam huff and puff for heavy oil reservoirs. The typical screening criteria for steam flooding requires reservoir pressure to be less than 5 MPa, the steam quality of conventional steam flooding in bottom hole is about 30%, heavy oil reservoir in Shengli Oilfield with character of deep burial depth, active edge and bottom water and high formation pressure (7-8 MPa), the increase of oil recovery using conventional steam flooding is not obvious, Therefore, the formation and development of steam chamber during steam flooding are studied by indoor physical simulation experiments, the feasibility of high-quality steam flooding under high pressure is analyzed. The experimental results show that the quality of steam injection has obvious influence on the expansion of steam chamber. As the steam quality increases under high pressure, the specific volume of underground steam increases, the formation time of steam chamber is shortened, the expansion distance of steam chamber increases, the effective steam flooding time is prolonged, and recovery rate improves obviously . Field tests of high-quality steam flooding under high presure were carried out in Gudao Zhongerbei heavy oil reservoir of Shengli Oilfield, the result shows that the bottom-hole steam quality of steam injection wells is 50 % and above (20% higher than conventional steam flooding), the steam chamber was effectively expanded and the performance of producing rate for production wells improves obviously. The recovery rate of the test area reached 52.1%, which was 16.8% higher than that of steam huff and puff. High-quality steam flooding technology was an effective way to improve the recovery rate of high-pressure heavy oil reservoirs.
29
Key words: heavy oil; steam flooding; pressure; steam quality; recovery factor
30 31 32 33 34 35 36 37 38 39 40 41 42 43
Introduction
257000, China.E-mail address: [email protected] (YanZhao).
Abstract
Steam flooding is an effective way to further increase oil recovery rate after huff and puff in heavy oil reservoirs [1-4]. The increase rate of oil recovery by successful steam flooding is very high all ove the world. According to the conventional steam flooding screening criteria, for heavy oil reservoirs with reservoir pressure higher than 5 MPa, it is not suitable to use steam flooding to improve oil recovery rate[5-7]. Shengli Oilfield has abundant heavy oil resources. By 2018, 557 million tons of heavy oil geological reserves have been produced in Shengli Oilfield. More than 90% of the productions is deep heavy oil with buried depth of 1000 1400 meters, and most of them have edge and bottom water [8-9]. Therefore, the pressure drop is slow using huff and puff method. It is very difficult for the pressure of heavy oil reserves with reservoir pressure to be reduced to 5 MPa. The field practice of conventional steam flooding (about 30% steam injection quality) has shown that when the reservoir pressure increase, the recovery factor of steam flooding decreases obviously [10-11]. In recent years, high-quality steam injection technology has made great progress [12-13]. Bottom-hole steam quality of Shengli Oilfield deep heavy oil reservoir has
44 45 46 47 48
increased from 30% to 50%. For this reason, physical simulation experiments of high- quality steam flooding under 7MPa condition have been carried out. These experiments are very helpful to both monitor the development of steam chamber during steam flooding, and study the feasibility of high- quality steam flooding under high pressure. This provides an effective way to increase oil recovery rate of high-pressure heavy oil reservoir.
49
1. Experimental design
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
1.1. Experimental device This experiment adopts a self-developed two-dimensional proportional high-pressure steam thermal recovery physical simulation device (Fig. 1). The simulation device consists of injection system, model body, output system, measurement and control system. The model body is a vertical two-dimensional high-pressure model, which can withstand 10 MPa pressure and 300 temperature. It can simulate the profile of vertical heterogeneity between injection and production wells. The injection system mainly composes of high-pressure constant-speed pump, steam generator, intermediate container, pipe and valve components, which can generate steam for injection with different quality. The main output system is the oil-water metering device, which completes the separation and measurement of the model produced liquid. The measurement and control system include pressure monitoring device and temperature acquisition device. The pressure monitoring device monitors the pressure at the inlet and outlet, and reflects the variation of model pressure in real time. The temperature acquisition device collects the temperature change at the temperature measuring point in the model in real time through thermocouples at each layer, and stores, processes and displays the temperature field map on computer.
66 67 68 69 70 71 72 73 74 75 76 77 78 79
Fig.1
Two-dimension physical model of steam recovery
1.2. Physical model According to the similarity criterion of steam flooding physical simulation, using Ng5 heavy oil reservoir in Zhongerbei of Gudao Oilfield as the prototype and combining with reservoir geological development parameters, a two-dimensional physical simulation model of vertical heterogeneity is established to simulate the cross-well profile of one injection and one production well. The model is 700 mm wide and 90 mm high. It has seven simulated layers in vertical direction. There are 17 thermocouples in each layer and 119 thermocouples in total (Table 1). Any temperature profile in the reservoir can be obtained by interpolation. The steam chamber distribution and the steam front in the vertical direction can be judged by the temperature profile. The tubing string is made of stainless-steel pipe with a diameter of 6 mm and is sliced at the reservoir to simulate the perforation section of field wells. The oil used in the experiment is the crude oil from the Zhongerbei formation in Gudao. The surface (50 ) dead oil viscosity is 3783
80 81 82 83
mPa·s, the surface dead oil density is 0.9764 g/cm3, the initial reservoir temperature is 65 C, the reservoir model pressure is 7 MPa, the production time is 25.7 min, and the steam injection speed is 25 mL/min. Table1
Physical property parameters of each layer thickness cm
permeability 10-3μm2
K1layer
1.59
1594
K2layer
1.33
1606
interlayer
1.49
K3layer
0.95
1495
K4layer
1.18
1477
interlayer
1.07
K5layer
1.39
Total
9.00
Layering/lamination
1381
84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106
1.3. Experimental scheme and steps Three experimental schemes have been designed. Scheme 1 injects steam with 10% steam quality, scheme 2 injects steam with 30% steam quality and scheme 3 injects steam with 50% steam quality. In order to make comparation, temperature field changes during steam flooding were monitored by temperature sensors, oil-water separation and quantitative analysis were carried out for the model produced liquid, production indexes of different schemes were determined, and the effects of steam injection quality on the effect of steam flooding development and steam chamber sweeping pattern were studied. The experimental include the following steps: model loading. Firstly, load the model with different particle sizes sand, and the air permeability is tested by single tube model to make the air permeability equal to the model permeability. The using sand is the fractured sand with uniform particle size after acid treatment. After filling the model by water injection sedimentation method, the water leakage test is carried out. The test pressure, 9 MPa, not reducing in 1h is regarded as qualified. Then the water in the model will be released. Vacuumized the model. And then be saturated with distilled water. The pore volume and porosity are measured by T-type. Model initialization. The oil saturation and irreducible water saturation of each layer are calculated by injecting the experimental oil into the model at a constant low speed until no water is produced at the outlet. The temperature and pressure of the model are adjusted to keep it stable at the simulated temperature and pressure for 12 hours. Steam flooding simulation under different experimental schemes. The steam injection rate is 25 mL/min. The inlet and outlet pressure and the temperature field of each layer are recorded regularly, and the oil production, water production and injection quantity are measured.
107
2.Experimental results and analysis
108 109 110 111 112 113 114
2.1. Variation of steam chamber It can be seen from the variation of longitudinal temperature field of scheme 1, scheme 2 and scheme 3 models with injection volume (fig. 2-4) that the steam quality of scheme 1 is 10%. Most of the injected steam is hot water, and the amount of dry steam is small. The latent heat of vaporization is low. The time efficiency of injecting heat is low. The temperature field expands slowly. When the amount of injected steam (water equivalent) reaches 3.0 PV, steam chamber begins to form in the upper permeable layer. With the continuous injection of steam, the steam
115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
chamber gradually expands forward. The steam drive ends when the steam injection amount (water equivalent) reaches 4.6 PV,. From the direction of the injection well to the production well, several different temperature zones are formed, namely, the steam chamber near the injection well, the condensation hot water zone behind the steam chamber, and the original temperature zone near the production well. The expansion distance of the steam chamber is small. Only about 1/10 of the well spacing, most of the models are hot water zones, accounts for nearly 6/10 of the well spacing. There is no steam chamber in the middle and lower permeable layers. It shows that, under the condition of 7 MPa pressure and 10% steam injection quality, the underground flooding mode is basically hot water flooding. The steam injection quality of scheme 2 is 30%, the expansion speed of temperature field is accelerated. When the injection volume reaches 2.2 PV, the steam chamber begins to form in the upper two permeable layers. The steam drive ends when the injection volume (water equivalent) reaches 5.5 PV,. The expansion distance of the steam chamber is larger than that of scheme 1, accounting for nearly one sixth of the well spacing, but the development of the steam chamber is still unsatisfactory. Scheme 3’s steam injection quality is 50%, and when the injection volume reaches 1.3 PV, the steam chamber begins to form in all upper three permeable layers. When steam injection volume (water equivalent) reaches 6.5 PV, steam flooding ends. The expansion distance of steam chamber increases obviously, approaching 1/2 of well spacing, reservoir temperature rises obviously, the expansion distance of steam chamber in upper permeable layer is larger, showing the characteristics of steam overlap. Compared with the steam chamber formation time, the steam flooding time and the expansion distance of the steam chamber at the end of steam flooding of scheme 1, scheme 2 and scheme 3, it can be found that with the increase of steam injection quality, the formation time of steam chamber decrease, the steam flooding time becomes longer, and the expansion distance of steam cavity becomes larger at the end of steam flooding. The reason is that in the process of steam flooding, when the reservoir is heated to the saturation temperature of the steam, the steam chamber starts to form. During this period, a large amount of steam is needed to condense into hot water, release heat to heat crude oil and rock. High quality of steam injection can take high latent heat of steam vaporization resulting in high time efficiency of injecting heat, shorter time of forming steam chamber and faster expansion speed. At the same time, heating and viscosity reduction are the main factors of steam flooding. The higher the quality of steam injection, the higher the enthalpy of heat carried, the more fully heated of the crude oil, the better the flow ability of the crude oil, the lower the mobility ratio of water to oil, the weaker the steam coning, and the more balanced of the steam advancing, so the steam flooding time becomes longer.
150 151
Fig.2
the temperature field in experimental scheme 1
Fig.3
the temperature field in experimental scheme 2
152 153
154
155 156 157 158 159 160 161 162 163 164 165 166 167
Fig.4
the temperature field in experimental scheme 3
2.2. Development effect By comparing the recovery percentage of three experimental schemes with the variation of injection pore volume multiple (Fig. 5), it can be seen that the ultimate recovery percentage of scheme 3 is 59.9%, the steam flooding time is the longest, the ultimate recovery percent of scheme 2 is 51.9%, the ultimate recovery percentage of scheme 1 is 45.6%. The steam injection quality increases from 10% to 50% under 7 MPa reservoir pressure, while the recovery percentage of steam flooding stage increases by 14.3%. The steam injection quality has a significant impact on the recovery of steam flooding. Increasing the steam injection quality can effectively improve the development effect of deep heavy oil steam flooding. The main reason is that when the steam injection quality is improved, the expansion distance of the steam chamber becomes larger, and the oil displacement efficiency of the steam chamber is obviously higher than that of the hot water zone at the same temperature, so the steam displacement recovery degree is obviously improved.
168 169
Fig.5
Change of recovery percentage in experimental scheme 1,2,3
170
3. Pilot test
171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187
3.1. Basic information of the test area The test area is located in the main part of Zhongerbei Ng5 heavy oil unit in Gudao, Shengli Oilfield. Four large well spacing groups with 141×200m and four small well spacing groups with 100×141m are deployed. The oil-bearing area is 0.51 km2 and the OOIP is 122×104t. The target stratum in the test area is gentle with buried depth of 1286-1316m and some certain edge water in the north. The effective thickness is 10.2m, the porosity is 31%, the average air permeability is 2300×10-3µm2, and the crude oil viscosity is 546.3 mPa·s under reservoir condition. It belongs to the fluvial facies deposited unconsolidated sandstone reservoir with high porosity and high permeability. Steam stimulation recovery development was started in October 1992 in the test area. Displacement characteristic curve method and numerical simulation method was used in this area, the steam stimulation recovery rates of large and small well spacing groups were 35.2% and 35.5% respectively. In October 2010, small well spacing groups changed to high quality steam flooding, by then the formation pressure ranged from 7 MPa to 8 MPa, the recovery percentage was 31.4% and the water cut was 89.0%. In March 2011, large well spacing groups turned to the same recovery method, and the formation pressure was 7 8 MPa, the recovery percentage was 33.5% and the water cut was 91.8%.
188 189 190 191 192 193 194 195 196 197
3.2. Steam injection status High quality steam injection boiler is used in this area. The field application shows that the steam quality at the outlet of the boiler can approach 99%. In order to reduce wellbore heat loss, high vacuum insulated tubing is used in wellbore steam injection string, and heat insulation bushing and heat insulation compensator are used to insulate hot spots of steam injection string. The apparent thermal conductivity coefficient of steam injection tubing string is only 0.0068W/(m· ). After adopting the above measures to improve bottom-hole steam quality, 8 steam injection wells were sampled and tested for bottom-hole steam quality under the 5 t/h steam injection speed. The actual bottom-hole steam quality can reach more than 50% and meet the requirements of high- quality steam flooding.
198 199 200 201 202 203 204 205 206 207 208 209
3.3. Test effect From the production curve of the test area, the daily oil production rate of 17 wells in four small well spacing groups increased from 20.2 t/d to 101 t/d, the total water cut decreased from 89% to the lowest 74.6%, the daily oil production of 21 wells in the four large well spacing groups increased from 61 t/d to 113 t/d, and the total water cut decreased from 89.7% to the lowest 85.5%. Up to June 2016, the daily oil production of eight well groups in the test area was 108 t/d, the total water cut was 90.4%, the cumulative oil production was 23.6×104 t, the recovery percentage was 52.1%, and the recovery factor increased by 16.8%. The cumulative oil production of four small well spacing groups was 10.3 ×104t, the stage oil-gas ratio was 0.16t/t, the recovery percent was 55.8%, and the recovery rate has been increased by 20.3%; the cumulative oil production of four large well spacing groups was 13.3 ×104t, the stage oil-gas ratio is 0.15t/t, the recovery percentage was 50.0%, and the recovery rate has been increased by 14.8%.
210
211 212 213 214 215 216 217 218
Fig.6
Production curve of pilot test
In October 2014, a sealed coring well 26XJ532 was drilled on the main stream line, 77.7 m away from the steam injection well in the 26-N533 small well spacing group. The average remaining oil saturation in core analysis was 19.8%, and the inter-well oil saturation was greatly reduced. The oil displacement effect of upper reservoir was better, and the remaining oil saturation in core analysis was only 15.7% (fig.7). After oil-water saturation correction, the average remaining oil saturation is 27.7%, the average oil displacement efficiency is 62.4%, and the upper reservoir oil displacement efficiency is 70.5%.
219 220
Fig.7
Remaining oil saturation of sealed coring well 26XJ532
221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245
4. Conclusion (1) Laboratory experiment results show that steam quality has a significant effect on the expansion of steam chamber during steam flooding. Under the condition of 7MPa, the formation time of steam chamber is shortened, the total steam flooding time is longer, and the expansion distance of steam chamber is larger at the end of steam flooding. At the same time, under the condition of 7MPa, as the steam quality increases, the steam flooding recovery is greatly improved. (2) High pressure and high steam quality flooding has achieved good results in Gudao Zhongerbei heavy oil unit of Shengli Oilfield. The steam flooding recovery rate is 52.1% at 7MPa reservoir pressure and 50% steam quality, which is increased by 16.8%. (3) Laboratory and field tests show that high dryness quality flooding technology is feasible, and it is an effective method to improve the recovery of high-pressure heavy oil reservoirs.
Acknowledgements This work was sponsored by National Science and Technology Major Project of China (2016ZX05011-003), Sinopec scientific research project (P17003).
References [1] Yue Qingshan,1998. Thermal technology for Steam Injection in Heavy Oil Reservoirs. Beijing: Petroleum Industrial Press, 26-147. [2] Liu Wenzhang,1997. Thermal engineering for heavy oil reservoirs. Beijing: Petroleum Industrial Press, 348-393. [3] Shen Pingping,2005. Thermal technology for EOR. Beijing: Petroleum Industrial Press, 23-56. [4] Yang Zhanwei, Zhao Qishuang, Chen Gang, 2012. Optimization of development mothods for heavy oil
246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266
reservoir of KS Oilfield. Fault-Block Oil
Gas Field, 19(1),21-24.
[5] Zhang Yitang, Li Xiuluan, Zhang Xia,2008. Four fundamental principles for design and follow-up of steam flooding in heavy oil reservoirs. Oil Drilling & Production Technology, 35(6),715-719 [6] Yue Qingshan, Li Pingke,1997. Effect of reservoir pressure on development result of steam drive. Special Oil & Gas Reservoirs, 4(4), 15-18 [7] Su Yuliang, Gao Haitao,2009. Influencing factors of thermal efficiency during heavy oil steam drive. Fault-Block Oil
Gas Field, 16(2), 72-74.
[8] Yang Yuanliang,2011. Pilot test of steam flooding in super heavy oil reservoirs in Shan 56 area. Journal of Oil and Gas Technology, 33(1), 142-144. [9] Tao Lei, Li Zhaomin, Bi Yiquan, Li Binfei,2010. Multi-combination exploiting technique of ultra-heavy oil reservoirs with deep and thin layers in Shengli oilfield. Petroleum Exploration and Development, 37(6), 732-736. [10] Cao Yanbin, Liu Dongqing, Wang Shantang, 2014. Three-dimensional physical simulation and application of chemistry assistant steam flooding on middle and deep heavy oil reservoir. Acta Petroleum SINICA, 35(4), 739-744. [11] Song Yang,2013. Optimization design of steam flooding for horizontal well in thin heavy oil reservoir. Fault-Block Oil
Gas Field, 20(2), 239-241.
[12] Shi Qinfang,2013. Special(Micro)Overheat Steam Generator Research and Application in Oilfield. Journal of Petrochemical Universities, 26(2), 63-67 [13] Shi Qinfang,2013. Design of the water treatment system for high quality steam generator. Automation & Instrumentation, 3(2), 65-66
Highlight (1) Laboratory experiments show that steam quality has a significant effect on the expansion of steam chamber during steam flooding. Under the condition of 7MPa, the formation time of steam chamber is shortened, the total steam flooding time is longer, and the expansion distance of steam chamber is larger at the end of steam flooding. At the same time, under the condition of 7MPa, as the steam quality increases, the steam flooding recovery is dramatically improved. (2) High pressure and high steam quality flooding has achieved good results in Gudao Zhongerbei heavy oil unit in Shengli Oilfield. The steam flooding recovery rate is 52.1% at 7MPa reservoir pressure and 50% steam quality, which is increased by 16.8%. (3) Laboratory and field tests show that high dryness quality steam flooding technology is feasible, and it is an effective method to improve the recovery of high-pressure heavy oil reservoirs.