Abstract: A shale gas field at southern margin of the Sichuan Basin commenced production in 2014. For assuring its engineering efficiency and development benefit, it is critical to accurately understand the geomechanics law and its application in various scales. Accordingly, 3D geomechanics models were built in the scales of the whole study area and the platform. These models are high-resolution models based on structure, geology, attributes and multi-scale natural fractures. Core, well logging and seismic data were used to finely describe the mechanical parameters, and a set of methods for establishing 3D pore pressure model for shale gas field was established. Advanced finite element simulator and large-scale parallel computing technology were applied to establish 3D stress field models with different planar resolutions for the whole study area and the platform. In order to accurately characterize the vertical heterogeneity of shale, the models are designed with a resolution of 0.5 m thick in target layers. Various data were utilized for quality control and calibration of these models, and new data were timely used to continually update these models. The accuracies of these models can reflect the direction, size, heterogeneity and anisotropy of the stress. The results show that in-situ stresses vary greatly at platforms, between wells and along the horizontal well sections. Such complex variations are the consequent reflections of rock textures (e.g. structural form, and multi-scale fracture system) and rock composition in various scales. These geomechanics models can meet various requirements for scale and accuracy in different applications in either the whole study area or any single well. The whole-area model can be used to optimize platform location and well location deployment, to evaluate the geologic storage capacity and resources, and to assess the mechanical stability of faults and fractured belts. The high-resolution platform model can be applied in analyzing borehole stability, managing drilling in real-time manner, optimizing fracturing design, and making post-frac comprehensive evaluation. These geomechanics models have been successfully integrated in the practices of geology-engineering integration. By iterative updating and in-time application, they facilitate the engineering efficiency and development benefits. The establishment of large-scale geomechanics models for development of shale gas fields, recording the first time in China, provides references for future operations.

Key words: geology-engineering integration, geomechanics, Longmaxi Formation, shale gas, Zhaotong National Shale Gas Demonstration Zone