热采环境泥岩层应力演化规律及破坏机理研究

Study on Stress Evolution and Failure Mechanism of Mudstone Layer in Thermal Recovery Environment

深入认识热采环境下泥岩层的应力演化规律及破坏机理,有助于科学有效地解决稠油藏注汽过程中的盖层破裂问题及隔夹层遮挡问题。首先,从理论上定量研究了热采油藏泥岩层的传热、增压机制,分析了变温、变压条件下泥岩层不同的应力演化规律及破坏模式;然后,针对一加拿大热采项目的盖层破坏事件,开展了泥岩盖层热-水-应力全耦合数值模拟研究,揭示了热采环境下泥岩层的破坏机理及关键影响因素。结果表明,热采环境中泥岩层应力演化主要受热增压影响;孔隙压力远高于注汽压力,峰值位于孔隙水最大热压力系数所对应的温度附近;孔隙压力峰值附近岩层可能发生拉伸破坏和剪切破坏。热采油藏合理注汽方案的制定必须充分考虑泥岩层的热-水-应力耦合效应。

The in-depth understanding of stress evolution and failure mechanism of the mudstone layer,in a thermal recovery environment,is helpful for scientifically and effectively solving the problem of cap rock cracking and interlayer blocking in the process of steam injection for heavy oil reservoirs.Firstly,the heat transfer and pressurization mechanism of the mudstone layer,in the reservoir thermal recovery process,are studied quantitatively,based on theory.The different stress evolution trends and failure modes of the mudstone layer are analyzed under variable temperature and pressure conditions.Then,using the cap rock fracture event as an example,which occurred in one of the thermal recovery projects in Canada,the heat-water-stress coupling numerical simulation of mudstone cap rock is performed.Thereby,the failure mechanism and key influencing factors of the mudstone layer,in the thermal recovery environment,are revealed.The results show that the stress evolution of the mudstone layer,in the thermal recovery environment,is mainly affected by heat-induced pressurization.Pore pressure is much higher than injection pressure and the peak value is located near the temperature corresponding to the maximum thermal pressure coefficient of pore water.The rock layers adjacent to the peak of the pore pressure are possibly subjected to tensile and shear damage.The development of a reasonable steam injection scheme,for the thermal recovery of reservoirs,must take into account the heat-water-stress coupling effect of the mudstone strata.