长宁区块页岩水化起裂机理及应用

MECHANISM OF SHALE HYDRATION CRACKING AND APPLICATION AT CHANGNING BLOCK

页岩储层大规模水力压裂后,大量压入地层的压裂液滞留在页岩地层中,会导致页岩与压裂液发生水化起裂作用,影响压后返排规律。为了探索页岩水化起裂机理,文章开展了压裂液对页岩的伤害实验、页岩的自吸及水化起裂实验,实验结果表明,压裂液滞留地层的积极作用(裂缝起裂扩展)和消极作用(水相圈闭损害)是同时存在的;页岩的自吸过程具有相同的趋势,可分为快速渗吸段、过渡段和平稳段三个阶段,不同的页岩裂缝发育程度、黏土矿物含量及浸泡时间对页岩自吸量的影响是不同的;页岩自吸后会引起页岩的裂缝扩展及次生裂缝的产生,增加裂缝复杂程度。同时,建立了页岩水化起裂预测模型,编制了页岩水化起裂分析软件,能够准确的预测页岩水化起裂情况。结合长宁区块A井区页岩气井焖井时间与测试产量关系统计,长宁区块最优的焖井时间为5~10 d,研究结果对于页岩气井焖井时间优化具有较好的指导意义。

After large-scale hydraulic fracturing of shale reservoirs,a large amount of fracturing fluid pressed into the stratum will remain in the shale formation,which will lead to hydration and fracturing of shale and fracturing fluid,affecting the back-flow after fracturing.In order to explore the mechanism of shale hydration cracking initiation,the damage experiment of fracturing fluid on shale and self-absorbing of shale and hydration initiation test are carried out.The experimental results show that,①the positive effect of the fracturing fluid retention in formation(crack initiation and extension)and the negative effect(water phase trap damage)are simultaneous;②the self-sucking process of shale has the same trend and can be divided into three stages,rapid infiltration stage,transition stage and stationary stage.The effects of shale fracture development,clay mineral content and soaking time on shale self-sucking is different;③shale self-sucking will cause shale crack propagation and secondary cracks,increasing the complexity of cracks.At the same time,the shale hydration cracking prediction model is established,and the shale hydration cracking initiation analysis software is compiled,which can accurately predict the shale hydration cracking.According to the statistics of the relationship between soaking time and test output in shale gas wells at Changning block A,the optimal soaking time at Changning block is 5~10 days.The research results have good guiding significance for shale gas well soaking time optimization.