Shale Gas Stress Analysis Method Based On Multi-Source Information

In the process of exploration and development of shale gas,the accurate stress can effectively guide the wellbore trajectory design and shale dessert prediction.On the stress prediction problem of shale gas exploration and development,we have studied two types of shale gas stress analysis methods based on multi-source information:(1)The stress calculation method based on "curvature + pre-stack elastic parameters" is improved: firstly,we deduced the "curvature-stress" equation,and the relationship between curvature properties and stress is established;then,we calculated the curvature data volume and Young’s modulus data volume based on the 3D seismic data;finally calculate the horizontal principal stress.In order to apply to shale gas exploration,this paper improves it from three aspects: 1.We choose the preferred filtering algorithm to process the curvature data,and obtained the curvature calculation results which could be better reflecting the structural form of the shale formation in strong structural form;2.We abandon the conventional stress calculation method which set the elastic parameter with a certain constant(Fixed approximation)of the entire study area,and use the elastic parameter(Young’s modulus)data which obtained by pre-stack elastic inversion instead which could adapt to the anisotropic characteristics of shale gas strata;3.We developed a method of the establishment of high-precision seismic interval velocity field,which is applied to calculate the deep structural map.The characteristics are more suitable for shale study area which gain more accuracy instead of the method based on the DIX formula.(2)We innovatively proposed a set of shale gas stress prediction technology based on formation pore pressure properties: we first calculate the seismic interval velocity field based on the high-precision interval velocity establishment method;and use the optimal Eaton + Fillippone method to calculate the pore pressure of the formation;then we calculate the horizontal structural strain data volume and the pre-stack elastic parameter data volume(Young’s modulus and Poisson’s ratio);finally,we take the stress model to analyze the shale formation stress by using the pore pressure data and elastic parameters comprehensively.The innovation of this technology: 1 we use the curvature data to calculate the horizontal strain parameters which solve the problem of setting the strain parameters in the stress model innovatively;2 We use the 3D edge-preserving denoising algorithm to process the key parameter(interval velocity)for pore pressure calculation which is well applicable to the low-porosity and low-permeability characteristics of shale gas formation(there is no large singularity within the formation).The above two methods all use the multi-source information such as post-stack 3D seismic data,pre-stack 3D seismic data,well logging data,and actual test data,therefore I give the name: Shale gas stress analysis method based on multi-source information.The analysis results of shale gas stress in Fuling area in Chongqing which indicates that the stress results are not only constrained by the structural forms,but also conform to the physical laws between stress and the formation pore pressure,which could be well applied to shale gas area with low porosity,low permeability and strong structural change in the strata.This method can be used to promote shale gas exploration and development in the future.