呼图壁储气库注采作业诱发应力场变化的机理及影响

Underground gas storage (UGS) in depleted hydrocarbon reservoirs is a strategic practice to cope with the growing energy demand in China. The Hutubi underground gas storage is the largest one in China. In response to summer gas injection and winter gas extraction the reservoir expands and contracts essentially elastically as a major consequence of the fluid pore pressure fluctuations. The mechanism and the potential consequences of the stress variations due to the deformation of the reservoir and the cap stratum are still to be studied. Firstly, the parameters about the geomechanical properties of the Hutubi gas storage reservoir and the cap stratum should be attained according the previous research work during the development of the Hutubi hydrocarbon reservoir and the construction of the Hutubi underground gas storage. Meanwhile, the in-situ stress field, the near and far field stress regime should be determined according to the former research findings. Secondly, one prediction model for stress variation law under the seasonal injection and extraction conditions shall be built up through the poroelastic theory and the deformation analysis method in reservoir space (DARS). At last, the critical stress boundary conditions for the activation and inerting of regional faults and fractures shall be established by the mature geomechanical theories. Abundant seismic observation data can be used to verify the prediction model and the critical stress boundaries. The potential research findings will offer scientific evidences for the interpretation and assessment of induced seismicity by the gas injection and extraction, and will offer technical supports for the long-term safe operation and management of the underground gas storage and the future increase of production capability. Therefore, the research is of great scientific, economic and social significance.

利用枯竭油气藏建设地下储气库是国家应对能源需求增长的重要举措。新疆呼图壁储气库是国内最大的储气库。储气库夏季注气和冬季抽气作业导致的储层内流体孔隙压力波动会诱发储层岩体膨胀和收缩变形，这种变形诱发的储层及盖层岩体的地应力场变化的机理和产生的可能影响仍有待研究。首先基于呼图壁气田和储气库开采和建设中已经形成的科学认识，获得储层和盖层岩体的地质力学属性参数。同时基于前人成果确定储气库工程区、近远场区区域地应力状态。然后基于多孔介质弹性理论和储层空间变形分析法建立储气库工程区在抽采循环作业条件下的地应力场变化预测模型。最后依据成熟的断层力学分析理论建立工程区区域断层的活化和惰化临界应力边界条件。利用可靠的地震观测数据来检验预测模型和应力边界条件的有效性。研究成果可为注采作业诱发地震的解释和评估提供科学依据，为储气库中长期安全运营和未来的扩容增产提供技术支撑，具有十分显著的科学、经济和社会意义。

利用枯竭油气藏建设地下储气库是国家应对能源需求增长的重要举措。新疆呼图壁储气库是国内最大的储气库。储气库夏季注气和冬季抽气作业导致的储层内流体孔隙压力波动会诱发储层岩体膨胀和收缩变形。呼图壁储气库运行初期出现了多次1.0级及以上地震，甚至出现了2次3.0级及以上地震，研究储气库工区注采诱发地层应力场变化及断层易滑动性对地震的影响具有重要意义。首先基于呼图壁气田和储气库开采和建设中已经形成的科学认识，获得储层和盖层岩体的地质力学属性参数。项目研究工作通过钻孔崩落数据和震源机制解反演了工区应力方向，并且基于钻孔崩落数据及钻孔诱发张裂缝，利用应力多边形理论来约束应力量值范围；然后，根据多孔介质弹性理论来估算气田开采和储气库周期注采情况下地层应力的变化，进而讨论断层滑动趋势与地震的关系；在此基础上，提出H储气库最大允许孔隙压力值。研究结果表明：①呼图壁地区最大水平主应力方向分别为N21°E 和~N23°E，呼图壁储气库工区应力方向为N23°E，=与区域构造应力场方向一致；② 呼图壁储气库注采前储层段水平最大、最小和垂直主应力量值分别为151.3 ± 11.6 MPa，72.7 ± 3.0 MPa和80.2 ± 1.2 MPa，应力结构为走滑型。③在呼图壁油气田开采前储层段应力结构处于为逆冲型应力状态，而随着油气开采逐步转换为走滑状态型，储气库的周期注采导致应力状态结构在在走滑与逆冲型间转换；④断层滑动趋势随着油气开采降低，而储气库注气会增加断层滑动的风险，其呼图壁断层滑动趋势值随着储气库周期注采而周期变化；⑤诱发地震发生的临界断层滑动趋势值为0.45±0.03，避免地震发生的最大允许地层孔隙压力为27.7MPa，并且该值可能会随着注采应力平衡而有所提高。项目研究成果可为注采作业诱发地震的解释和评估提供科学依据，为储气库中长期安全运营和未来的扩容增产提供技术支撑，具有十分显著的科学、经济和社会意义。