3D Geomechanical Modelling for Complex Geological Setting: A Case Study from XGS Field

Abstract

A 3D geomechanical model is built for the XGS field, located in Sichuan province, onshore China. The field is in a faulted anticline consisting of three main reservoir layers. The main reservoirs are in the crest of an anticline structure bounded between major revers faults. The model captures all the structural complexities and the spatial variation of the geomechanical properties and parameters for the entire XGS field. The structural model is built using the interpreted horizons and faults form the surface seismic tied to the markers interpreted from the well data. The 3D grid is constructed for the entire field, extended to the ground level, to use as a framework for the 3D geomechanical model. The well-centric geomechanical models prepared for the 14 offset wells are used in combination to the surface seismic attributes to model the lithology and petrophysical properties for the entire grid. These data are then used to calculate and propagate the geomechanical properties and parameters. The 3D geomechanical model is designed to captures the spatial variation of pore pressure, in-situ stresses, the rock mechanical properties and parameters. The grid has higher resolution in the main target for the underground gas storage (UGS) operation and its immediate overburden caprock layer. This is done to capture and investigate the vertical and lateral variations in the vicinity of the UGS reservoir in more detail. The rock mechanical properties and parameters are dominantly governed by the lithology. This is while the pore pressure and the in-situ stresses are mainly governed by the geological structure. That has been said, a stress contrast is observed between the shale and carbonate layers. The model suggests that the field is in a strike-slip stress regime. The reservoir rock which consists of fractured dolomite is competent and stiff while the shale caprock is relatively weaker. A comprehensive approach is developed to capture the complexities of the structure and properties of the XGS field. A robust workflow is implemented to propagate the geomechanical properties and parameters to maintain their consistency for the entire studied area.