碳酸盐岩储层孔洞与水力裂缝扩展相互作用的力学机理研究

Successful development in carbonate reservoirs requires vugs and caves should be connected through hydraulic fracturing because fossil resources in carbonate formations are mainly stored in those vugs and caves. However, few previous studies investigated the influence of vugs and caves on the propagation of hydraulic fractures, thereby it is not clear how fractures can connect those carbonate vugs and caves. This unclear problem leads to the difficulty of design and operation for the hydraulic fracturing in carbonate reservoirs. Therefore, the objective of this project proposal is to investigate and solve this problem from the standpoint of rock mechanics. The key methodology includes the tri-axial hydraulic fracturing experiment and numerical simulation. In the experiment, the artificial vugs and caves with various sizes, shapes, and directions are contained in the carbonate cubic sample. The acoustic emission and CT scanning are used to trace fracture trajectory. Based on the experiment, the mechanical effect of vugs and caves is determined, and a prediction model is developed to simulate the behavior when the hydraulic fractures reach the vugs and caves. The behavior includes passing through, stopping, and detouring. Finally, a numerical simulation model is established and provides theoretical and technical support for hydraulic fracturing in the vuggy carbonate formation.

水力裂缝沟通孔洞储集空间是保持碳酸盐岩油气高产的根本关键。目前孔洞与水力裂缝的相互作用力学机理不明确，水力裂缝在孔洞储集空间的扩展规律不清楚，导致碳酸盐岩大型深穿透酸压设计与施工缺乏理论依据、效果不佳。针对这一难题，围绕碳酸盐岩孔洞与水力裂缝的相互作用力学机理的科学问题，利用地质和测井资料以及井下岩心和天然露头研究孔洞的尺度、形态与空间分布特征，制备含孔洞的碳酸盐岩岩心开展大型真三轴水力压裂物理模拟实验，通过声发射监测和CT扫描技术表征水力裂缝扩展过程，分析水力裂缝扩展与孔洞之间的相互力学作用规律，建立水力裂缝遇到孔洞后的停滞、贯穿和转向的多尺度判别模型，发展含孔洞碳酸盐岩储层水力裂缝扩展模型与数值计算方法，揭示碳酸盐岩孔洞的尺度、形态与分布对水力裂缝扩展的力学影响机理，为碳酸盐岩储层改造提供理论支撑与技术指导。

针对缝洞型碳酸盐岩储层酸压设计与施工过程中水力裂缝在孔洞储集空间的扩展力学机理不明确和沟通规律不清楚的难题，利用地质和测井资料以及井下岩心和天然露头研究了孔洞的尺度、形态与空间分布特征，制备了含孔洞的碳酸盐岩岩心并开展了大型真三轴水力压裂物理模拟实验，通过声发射监测和CT扫描技术表征水力裂缝扩展过程，分析了水力裂缝扩展与孔洞之间的相互力学作用规律，解决了碳酸盐岩孔洞与水力裂缝的相互作用力学机理的科学问题，建立了水力裂缝遇到孔洞后的停滞、贯穿和转向的多尺度判别模型，发展了含孔洞碳酸盐岩储层水力裂缝扩展模型与数值计算方法，揭示碳酸盐岩孔洞的尺度、形态与分布对水力裂缝扩展的力学影响机理，为碳酸盐岩储层改造提供理论支撑与技术指导。项目成果在新疆塔里木盆地缝洞型碳酸盐岩储层酸化压裂储层改造设计中得到了应用，效果良好。