大尺度离散裂缝的渗透率应力敏感研究——以顺北油田为例

Study of permeability stress sensitivity of large-scale discrete fracture:a case study of Shunbei Oil Field

为解决大尺度离散裂缝渗透率应力敏感模型针对性不强的问题,文中基于裂缝介质内秉渗透率和离散裂缝充填长方体支撑物模型,建立了大尺度离散裂缝的内秉渗透率-应力解析模型,分析了裂缝渗透率与孔隙压力、裂缝渗流物理/力学参数的关系。研究表明:当裂缝面孔隙度大于0.8时,渗透率损失程度随着孔隙度的增加快速增加,导致大尺度离散裂缝和小尺度连续裂缝渗透率应力敏感的差异;同时,弹性模量平均每下降1000 MPa,渗透率应力敏感指数增加19.26%,而泊松比对应力敏感指数的影响并不显著。文中建立的内秉渗透率应力敏感模型在顺北油田生产动态数值模拟研究中取得了较好的应用效果。

In order to solve the problem that the permeability stress sensitivity model of large-scale discrete fracture is not very targeted,an analytical model of internal permeability variation with pore pressure of large-scale discrete fracture is established based on the internal permeability of fracture medium and the discrete fracture model filled with cuboid support,and the relationships among fracture permeability and pore pressure,physical parameters and mechanical parameters of fracture seepage are analyzed.The research shows that the extent of permeability loss increases fast with porosity increasing when the fracture porosity is higher than 0.8,which leads to the difference of permeability stress sensitivity between large-scale discrete fractures and small-scale continuous fractures.Meanwhile,every 1,000 MPa decrease in Young′s modulus will result in 19.26%increase in permeability stress sensitivity index,while the effect of Poisson′s ratio on stress sensitivity index is not obvious.The proposed stress sensitivity model of internal permeability has achieved a satisfying result in numerical simulation study in Shunbei Oil Field.