页岩吸水对储层的作用机理研究

Study on Shale Water Absorption Mechanism on Reservoir

水力压裂导致的页岩吸水使储层结构与矿物组分发生改变,开展页岩吸水研究对指导页岩气开发具有重要意义。对页岩吸水过程进行动态监测,分析页岩吸水对储层结构与矿物组分的影响规律,形成相关定性与定量分析方法。研究结果表明:1)水在黏土矿物等组分的吸水能力作用下通过原生裂缝快速进入页岩内部,随后发生缓慢渗吸过程,矿物溶解及水化作用的进行导致页岩在原生裂缝附近产生新的次生裂缝;2)黏土矿物在页岩吸水前期快速发生水化作用,水化作用主要发生于富含Na+与SO 2-4的矿物组分中,分析认为伊利石是黏土矿物发生水化作用的主要组分;3)铁白云石等脆性矿物的溶解强度明显高于黏土矿物的水化作用强度,分析认为脆性矿物溶解与黏土水化作用共同导致页岩吸水前后矿物组分改变。通过定性与定量分析页岩吸水过程储层结构与矿物组分的变化,初步获取了页岩吸水对页岩结构与组分的影响规律,以期指导实际生产开发。

Shale water absorption caused by hydraulic fracturing changes the reservoir structure and mineral composition.It is of great significance to conduct shale water absorption research to guide shale gas development.Dynamically monitor the process of shale water absorption,analyze the influence of shale water absorption on reservoir structure and mineral composition,and form relevant qualitative and quantitative analysis methods.The research results show that:1)Under the action of the strong water absorption capacity of clay minerals and other components,water quickly enters the interior of the shale through the primary fracture,and then a slow imbibition process occurs,the progress of mineral dissolution and hydration results in new secondary fractures of shale near the primary fracture.2)Clay minerals rapidly hydrated in the initial stage of shale water absorption.Hydration mainly occurred in mineral components rich in Na+and SO 2-4.Analysis indicated that illite was the main component of clay minerals hydrated.3)The dissolution strength of brittle minerals such as iron dolomite is significantly higher than the hydration strength of clay minerals.The analysis shows that the dissolution of brittle minerals and clay hydration together lead to changes in mineral composition before and after shale water absorption.By qualitatively and quantitatively analyzing the changes in the reservoir structure and mineral composition during shale water absorption,the influence law of shale water absorption on the shale structure and composition was preliminarily obtained in order to guide the actual production and development.