基于微纳米孔隙理论的页岩气储层岩石物理建模方法

A new rock physics model method for shale on the theory of micro-nanopores

页岩储层由于其复杂的构造和孔隙特征,目前一般的岩石物理模型无法对其进行精确描述.微纳米孔隙作为页岩气主要的储集空间,对页岩整体弹性参数有较大影响.干酪根作为页岩中重要的有机质矿物,在页岩中的赋存状态随成熟度不同而变化,同时干酪根也是纳米级孔隙的主要发育场所.目前常规的岩石物理建模方法没有体现微纳米孔隙的作用,同时较少考虑不同成熟度下干酪根对页岩储层弹性性质的影响.本文采用一种微纳米孔隙理论描述页岩微纳米孔隙特性,考虑微纳米孔隙和不同成熟度下干酪根的赋存状态,应用上述微纳米孔隙模型、各向异性SCA-DEM模型、各向异性Eshelby-Cheng模型和Brown-Korringa固体替换方程等建立一种新的页岩储层岩石物理模型.利用中国西南某工区页岩气井对该模型进行验证,模型预测的横波速度与测井速度拟合较好.结果表明不同干酪根成熟度的页岩岩石物理建模结果具有一定的差异,据此可大致区分该工区井的干酪根成熟度;最后对微纳米孔参数进行正演分析,结果反映了页岩的纵横波速度随微纳米孔隙参数的变化趋势.

Due to the complex structure and pore properties of shale reservoir,the current general rock physical model cannot accurately describe the shale reservoir.As the main storage space of shale gas,micro-nanometer pores have a great influence on the overall elastic parameters of shale.As an important type of organic mineral in shale,the state of kerogen in shale varies with maturity.Meanwhile,kerogen is also the primary place for the growth of nanometer pores.Currently,conventional rock physical modeling methods cannot reflect the role of micro-nanometerpores,while the influence of kerogen at different maturity on the elastic properties of shale reservoir is seldom considered.We adopt a theory of micro-nanometer pore to describe its characteristics.Considering the micro-nanometer pores and the state of kerogen at different maturity,we establish a new rock physical model by applying the above micro-nanometer pore model,anisotropic SCA-DEM model,anisotropic Eshelby-Cheng model and Brown-Korringa solid substitution equation.The model is verified by using a shale gas well in a working area in southwest China,and the shear wave velocity predicted by the model is well matched with logging velocity.There are some disparities between the results of the rock physical model of shale at difference maturity of kerogen.Therefore,we can roughly distinguish the maturity of kerogen in this work area.The forward analyses of micro-nanometer pores parameters reflect the variation trend of the primary wave and shear wave of shale with the micro-nanometer pores parameters.