基于嵌入离散裂缝的页岩气藏视渗透率模型

A Stochastic Permeability Model for Shale Gas Reservoirs Based on Embedded Discrete Fracture Model

页岩储层具有不同类型的储集空间,但综合考虑不同储集空间,对页岩储层渗透率进行评价的模型未见报道.基于嵌入离散裂缝模型,建立的页岩气藏视渗透率模型包括4个步骤:(1)构建天然裂缝、有机质和无机质的空间分布模型;(2)筛选不同类型储集空间的渗透率计算方法;(3)基于嵌入离散裂缝模型,结合空间分布模型和渗透率计算方法,建立数值模拟模型;(4)在模型的入口和出口端施加压差,求得一定压差下通过该岩心的气体流量,采用达西定律得到该页岩气藏的视渗透率.其计算结果与文献报道的渗透率实验值吻合较好.通过对不同因素的探讨,结果表明,天然裂缝对页岩气藏视渗透率的贡献大于无机质和有机质孔隙.因此,计算页岩视渗透率时有必要对天然裂缝、有机质和无机质孔隙进行综合考虑.

Shale reservoirs have different types of pore spaces,however,relevant studies on measuring the apparent permeability（AP）of shale gas reservoirs with considering different pore space have not been reported.A stochastic permeability model is proposed based on the embedded discrete fracture model（EDFM）in this study,which includes four steps.（1）The spatial distribution model of natural fracture,organic matter and inorganic matter is established.（2）Different permeability calculation methods are selected for different types of pore space.（3）The numerical simulation model is established on the basis of EDFM,using the spatial distribution model and different permeability calculation methods.（4）The gas flow rate is obtained by numerical simulation method after giving different pressures at the inlet and outlet of the model.Then the AP of this shale gas reservoir can be measured through the Darcy＇s law.The results of the model are in good agreement with the experimental results reported in literature.The effect of different pore space types,distribution and some other characteristics were analyzed.Results show that the contribution of natural fractures to AP is greater than that of matrix pores.Therefore it is crucial to take the effect of different pore space types into account in the process of calculating shale gas AP.