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Gas flooding is one of the important technologies to enhance oil recovery and contributes over one third of world's EOR production. This paper provide a research method based on the combination of gravity assisted gas drainage and pattern gas flooding, trying to solve the problem that formation structure is complex possessing large dip angle and small formation amplitude concurrently. This design is finally applied in scheme of H Reservoir which includes H-L Reservoir and H-Y Reservoir. Gravity assisted gas drainage and pattern gas flooding has been applied separately in the development of structural higher part and structural lower part. Laboratory physical simulation experiment, fine reservoir description and residual oil distribution have been researched to obtain higher oil recovery and gas-oil exchange rate. Multiple series of well patterns have been designed to according with multi-layer reservoirs. Stereoscopic well pattern will be reconstructed with gas flooding in the lower layers and existing development mode in the upper layers. This design has been used in the reservoir scheme of sandstone reservoir H. The combination gas flooding design and relative research methods proposed in this paper have been implemented in the reservoir scheme of H Reservoir. The design and development model was applied in the H-L Reservoir enhanced recovery program and field practice. After 20 years’ prediction, the cumulative gas injection was about 100 Bcf, the cumulative oil production was about 15 MMBbls, the water content at the end of the period was reduced to 60%, and the degree of recovery was improved by more than 20 percentage points compared with the water drive. The design and development model was applied in the H-Y Reservoir enhanced recovery program and field practice. After 30 years’ prediction, the cumulative condensate oil production was about 15 MMBbls, and the cumulative condensate gas production was more than 1000 Bcf. The EOR at the end of the test period was improved by over 28 percentage points compared with that of the depletion program. The improved EOR technique of combination of gravity assisted gas drainage and pattern gas flooding is creatively applied in formation with large dip angle and small structure amplitude concurrently in this paper, and bring about a striking effect. Other technologies such as fine reservoir description, stereoscopic well pattern, perforation upward layer by layer, GAGD, et al. will also achieve jelly results. In addition, the application of CO2 GAGD - pattern flooding could converse into CCUS later, while HC- GAGD - pattern flooding could converse into gas storage later.
Gas flooding is one of the important technologies to enhance oil recovery and contributes over one third of world's EOR production. This paper provide a research method based on the combination of gravity assisted gas drainage and pattern gas flooding, trying to solve the problem that formation structure is complex possessing large dip angle and small formation amplitude concurrently. This design is finally applied in scheme of H Reservoir which includes H-L Reservoir and H-Y Reservoir. Gravity assisted gas drainage and pattern gas flooding has been applied separately in the development of structural higher part and structural lower part. Laboratory physical simulation experiment, fine reservoir description and residual oil distribution have been researched to obtain higher oil recovery and gas-oil exchange rate. Multiple series of well patterns have been designed to according with multi-layer reservoirs. Stereoscopic well pattern will be reconstructed with gas flooding in the lower layers and existing development mode in the upper layers. This design has been used in the reservoir scheme of sandstone reservoir H. The combination gas flooding design and relative research methods proposed in this paper have been implemented in the reservoir scheme of H Reservoir. The design and development model was applied in the H-L Reservoir enhanced recovery program and field practice. After 20 years’ prediction, the cumulative gas injection was about 100 Bcf, the cumulative oil production was about 15 MMBbls, the water content at the end of the period was reduced to 60%, and the degree of recovery was improved by more than 20 percentage points compared with the water drive. The design and development model was applied in the H-Y Reservoir enhanced recovery program and field practice. After 30 years’ prediction, the cumulative condensate oil production was about 15 MMBbls, and the cumulative condensate gas production was more than 1000 Bcf. The EOR at the end of the test period was improved by over 28 percentage points compared with that of the depletion program. The improved EOR technique of combination of gravity assisted gas drainage and pattern gas flooding is creatively applied in formation with large dip angle and small structure amplitude concurrently in this paper, and bring about a striking effect. Other technologies such as fine reservoir description, stereoscopic well pattern, perforation upward layer by layer, GAGD, et al. will also achieve jelly results. In addition, the application of CO2 GAGD - pattern flooding could converse into CCUS later, while HC- GAGD - pattern flooding could converse into gas storage later.
This paper provide several improved miscible assistants, trying to mitigate the problem that CO2 miscible flooding is difficult to achieve in reservoirs because of the high miscible pressures, which leads to a lower recovery up to expectations. These miscible assistants could be easily mixed with crude oil by adding into CO2 and reduce the interfacial tension to drive down the minimum miscible pressure (MMP) in order to enhance sweep efficiency. Some efforts have been made to improve this situation. The effective method is to draw the experiences from structure characteristics of surfactants applied in micro emulsion of CO2-water systems. Amphiphilic organic assistants were designed to synthetize with fluoro-alkane chains and non-fluoro-OAc chains as the CO2-philic ends, as well as alkane structure as the lipophilic ends. The minimization of MMP of CO2 miscible processing assistants has been analyzed and optimized by surface tension testing in CO2-kerosene system and CO2-crude oil system. The crude oil was obtained from field test pilot in L Reservoir. The results of interfacial tension tests show that per-acetylated glucose dodecyl ester molecules have the ability to lower the interfacial tension most in these five kinds of new miscible processing assistants in two categories. Citric acid triisopropyl ester molecules take the second place, and others almost make no difference. The probable reason is that kerosene is mainly composed of C12 and lack of heavy components, which cause a weak interaction between independent hydroxyl of citric acid and tartaric acid assistant and hydrogen bond of kerosene. The results of interfacial tension tests show that all these miscible assistants possess good effects on minimizing the interfacial tension of the CO2-crudes system, and could also definitely reduce the MMP. Among these, per-acetylated glucose dodecyl ester molecules and citric acid isopropyl ester molecules perform most excellent, and could decrease the MMP of CO2 flooding by 27.5%. The assistants have been implemented in the CO2 flooding plan of L Reservoir with 4 gas injectors and 15 producers. After 15 years’ development simulation, cumulated oil production will reach 3.4 MMbbl with recovery increasing from 41.6% (only CO2 flooding) to 46.6%. Injection test shows that 1400 tons CO2 has been injected with 3800 bbl oil produced. The improved miscible assistants provided perform as well as other existing assistants in reducing interfacial tension and enhancing sweep efficiency in CO2 flooding. Compared with assistants of light hydrocarbon, these assistants require a little quantity to improve the miscible flooding, which could break the economic limits. Compared with the traditional fluoride assistants, these assistants are quite different in molecular structure and could cause little pollution and have been applied in field test.
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