针对页岩储层流固耦合作用影响多尺度流体流动规律认识不清的问题,运用应力敏感实验和Biot系数测定方法,分别研究页岩基质与裂缝的固有特征对其应力的敏感程度,分析微观渗流与宏观有效应力的相互作用关系;基于有效应力原理,建立了页岩储层基质-裂缝孔隙度和渗透率在有效应力作用下的数学模型,分析了不同流固耦合参数对页岩储层多尺度渗流运动的影响。研究表明:基质和裂缝的平均应力敏感系数分别为0.220和0.081,基质的应力敏感性强于裂缝的应力敏感性;基质和裂缝的平均Biot系数分别为0.310和0.710,基质的Biot系数小于裂缝的Biot系数,裂缝发育的储层孔隙压力对储层产能的影响不能忽略;法向刚度、弹性模量、泊松比、初始孔隙度越小,Biot系数越大,基质和缝网的流固耦合作用越强,渗透率下降越明显;解吸附膨胀作用造成页岩骨架颗粒的变形,页岩基质流固耦合作用增强;有支撑剂填充的人工裂缝,支撑颗粒越大、铺砂层数越多,裂缝的法向刚度越大,裂缝导流能力越强,流固耦合作用越弱。该渗流模型更全面地考虑流固耦合力学参数的影响,能更精确地分析流固耦合作用对不同尺度页岩渗流规律的影响,极大地简化计算分析且提升计算速度。研究成果可为页岩储层的有效开发提供理论依据。
In response to the insufficient understanding of multi-scale fluid flow behavior under fluid-solid coupling in shale reservoirs,stress sensitivity experiments and Biot coefficient measurements were employed to study the inherent characteristics of shale matrix and fractures and their sensitivity to stress respectively.The interactions between micro-scale seepage and macro-scale effective stress were analyzed.Based on the effective stress principle,mathematical models were established for shale reservoir matrix-fracture porosity and permeability under effective stress,and the impacts of various fluid-solid coupling parameters on multi-scale flow in shale reservoirs were analyzed.The results show that the average stress sensitivity coefficients of the matrix and fractures are 0.220 and 0.081 respectively,indicating the matrix is more stress-sensitive than fractures.The average Biot coefficients of the matrix and fractures are 0.310 and 0.710 respectively,indicating the matrix's Biot coefficient is smaller than that of the fractures,thus pore pressure in fracture-developed reservoirs has a non-negligible impact on reservoir productivity.The smaller the normal stiffness,elastic modulus,Poisson's ratio,and initial porosity,the larger the Biot coefficient,and the stronger the fluid-solid coupling interaction between the matrix and fracture network,resulting in more obvious permeability reduction.Gas desorption-induced expansion causes deformation of shale matrix grains,enhancing fluid-solid coupling in the matrix.In proppant-filled fractures,larger proppant size and more layers of sand increase the normal stiffness of fractures,thereby improving fracture flow conductivity and weakening fluid-solid coupling effects.The proposed seepage model more comprehensively considers the influence of fluid-solid coupling mechanical parameters and can more accurately analyze the impact of fluid-solid coupling on multi-scale seepage behavior in shale,greatly simplifying calculations and improving computation speed.The findings provide a theoretical basis for the effective development of shale reservoirs.
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