超临界二氧化碳压裂过程中注入压力对致密砂岩力学特征的影响

Effects of supercritical carbon dioxide fracturing on rock mechanics characteristics of tight sandstone gas reservoirs

张艳 楼一珊 牟春国 白建文 贾建鹏

ZHANG Yan LOU Yishan MOU Chunguo BAI Jianwen JIA Jianpeng

长江大学石油工程学院 中国石油长庆油田分公司油气工艺研究院

School of Petroleum Engineering, Yangtze University, Wuhan, Hubei, 430100, China Oil & Gas Technology Research Institute of Petro China Changqing Oilfield Company, Xi’an 710018, China

针对致密砂岩气藏采用超临界二氧化碳压裂技术开发中，未考虑二氧化碳流体对储层岩石力学影响，从而导致设计压裂施工参数与现场实际不吻合问题，取苏里格气田2 800 m左右石盒子组地层岩心，在围压38 MPa、温度85 ℃下，模拟地层条件开展超临界二氧化碳压裂致密砂岩岩石力学特征实验，测试二氧化碳注入压力从3 MPa增加到35 MPa，然后加轴向压力至岩石破坏，获得致密砂岩岩石应力—应变曲线。研究表明，随超临界二氧化碳注入压力增大，致密砂岩抗压强度、弹性模量均减小，泊松比则增加，脆性指数先略微增大而后呈减小趋势。拟合出脆性指数与二氧化碳注入压力的关系式，相关系数为0.903 6，注入压力为4.55 MPa时脆性指数极值为0.483 5。超临界二氧化碳压裂时应考虑注入压力对岩石力学参数的影响，弹性模量、泊松比、脆性指数等岩石力学参数影响致密砂岩裂缝起裂及扩展规律。

Aiming at the development of supercritical carbon dioxide fracture on tight sandstone gas reservoirs, the carbon dioxide fluid effect on rock mechanics is not considered, and the fracturing parameters are not consistent with the oilfield. The test of rock mechanics on tight sandstone by supercritical carbon dioxide fracturing in simulating lab test Confining pressure 38 MPa and temperature 85 ℃, injection pressure of supercritical carbon dioxide is from 0 to 35 MPa. Axial pressure on the tight sandstone result in damage, the stress - strain curve of tight sandstone rock was obtained. With the increase of supercritical carbon dioxide injection pressure, the compressive strength and elastic modulus of tight sandstone decreases, Poisson’s ratio increases, and the brittleness index increases first and then decreases. The fitting brittleness index and carbon dioxide injection pressure are several binomial relations. The maximum of brittleness index is 0.483 5 when injection pressure is equal to 4.55 MPa. The results show that the influence of injection pressure on rock mechanics parameters should be taken into account in supercritical carbon dioxide fracturing. Rock mechanics parameters such as elastic modulus, Poisson’s ratio and brittleness index should influence the initiation and propagation law of cracks in tight sandstone in the late stage.

10.13639/j.odpt.2019.02.019