基于页岩岩石物理等效模型的地层压力系数预测方法

Prediction for formation pressure coefficients based on an equivalent petrophysical model of shale

近年来页岩气的勘探开发实践表明其产量与压力系数呈正相关关系,但准确的地震预测难度较大。页岩气储层富含有机质及有机质孔隙,其矿物组分及微观结构相比常规储层更复杂。为此,构建了一种适用于海相页岩的岩石物理模型,并提出了一种基于该模型的页岩地层压力系数预测技术。首先结合页岩储层微观结构特征,针对骨架矿物的差异性,分别采用自洽(SCA)模型和微分等效介质(DEM)模型模拟得到背景介质,结合孔隙及流体等特征,建立等效岩石物理模型;进而通过计算背景介质体积模量及饱和流体等效岩石体积模量,发现两者的差异与实钻井压力系数正相关,并建立地震预测模型;最后推导建立了基于Gray近似弹性阻抗的体积模量直接反演方法,实现了页岩地层体积模量及压力系数的定量预测。实际数据试验表明预测结果与实钻井及后验井吻合度较高。

In recent years,shale gas exploration and development have shown a positive correlation between shale gas production and pressure coefficients,but the accurate seismic prediction is difficult.Shale gas reservoirs contain rich organic matter and pores,and the mineral composition and microstructure are more complex than those of conventional reservoirs.Therefore,this paper built a petrophysical model suitable for marine shale and proposed a coefficient prediction technology for shale formation pressure.Firstly,in combination with the microstructure characteristics of shale reservoirs and the difference in supporting minerals,the background medium was simulated by SCA and DEM models separately,and an equivalent petrophysical model was constructed given the characteristics of pores and fluids.Secondly,the bulk modulus of the background medium and the equivalent rock bulk modulus of saturated fluids were calculated,and it was found that the difference between the two moduli positively correlated with the actual drilling pressure coefficient.On this basis,a seismic prediction model was built.Finally,a direct inversion method for the bulk modulus of Gray approximation-based elastic impedance was derived and developed,which realizes the quantitative prediction of the bulk modulus and pressure coefficients of shale formation.The predicted results are in good agreement with actual drilling and posterior wells.