Study on Filtration Property of Hypercritical CO2 Fracturing Fluid for Shale Reservoirs
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摘要: 压裂施工过程中,压裂液的滤失量是影响压裂裂缝几何形态和压裂效果的主要因素,但目前中国还没有对页岩储层超临界CO2压裂液滤失规律实验方面的报道。因此,结合中国典型页岩气储层特征,研究了非线性滤失条件下,不同初始相态的CO2压裂液在地层岩心中的滤失规律,在此基础上分析了CO2压裂液滤失规律的主要影响因素,以及不同实验条件下CO2压裂液的滤失机理。实验结果表明,CO2压裂液的滤失规律受注入压力、压差、裂缝开启度及压裂液黏度等因素的影响,随着注入压力、压差、裂缝开启度的增大,CO2压裂液滤失速率增大;不同滤失实验条件下,影响CO2压裂液滤失规律的主导因素不同,当CO2压裂液处于超临界状态(7.38 MPa,31.1℃)时,由于黏度较大,超临界CO2压裂液的滤失系数相对较小。Abstract: Filter loss of fracturing fluid plays a major role in the geometry of fractures created by the fracturing fluid and the performance of fracturing. Reports on the filtration property of hypercritical CO2 fracturing fluid used in shale formation fracturing have not been found at present. Experiments have been conducted on shale reservoir cores (buried at 1,300-2,300 m, with natural fractures developed) taken from the Longmaxi Formation in Sichuan Basin, using a self-made filtration simulator, to study the filtration property of CO2 fracturing fluids with different initial phase states, at 55℃ and (confining pressure) 20 MPa, and different injection pressures and back pressures. Analyses of the experimental data indicate that in the conditions mentioned above, the filtration coefficient of CO2 fracturing fluids is between 1.00×10-4 m/min0.5 and 48.17×10-4 m/min0.5, with the spurt loss being negative. The filtration rate of CO2 fracturing fluid increases with increases in injection pressure, differential pressure, and the widths of fractures. The dominant factor affecting the filtration property of CO2 fracturing fluid in different conditions is different; at hypercritical state (7.38 MPa, 31.1℃), the CO2 fracturing fluid, because of its high viscosity, has a lower filtration coefficient.
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Key words:
- Shale reservoir /
- Hypercritical CO2 /
- Fracturing fluid /
- Filtration property
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