Comprehensive Stress Modeling Approach for High Topography-Complex Geological Structure of XGS Field

Abstract

ABSTRACT: The magnitude and orientation of the in-situ stresses are greatly impacted in areas where the ground elevation changes dramatically within the field boundaries. The stress model for XGS field, located in onshore China, is constrained using a comprehensive workflow starting from analyzing the wellbore scaled data to a full field finite element numerical model. The well data from 14 offset wells are used to constrain the magnitude and orientation of the principal stresses in the XGS field. Because of the significant difference in the ground elevation of the offset wells, the calculated in-situ stresses are associated with some level of errors in the 1D models. This is corrected to some extend by calculating the stresses using a 3D modeling approach. Subsequently, a 4D finite element numerical model is used to capture the impact of the complexities in geological structure and high topography changes in XGS field. The findings from the 4D model show that the state of stresses in the shallow sections within the high topography structure tend to be under normal stress regime which gradually changes to strike-slip stress regime in the deeper section. 1. INTRODUCTION The XGS underground gas storage facility currently operates in a depleted gas reservoir located in the Sichuan province, Southwest China. The facilities are constructed during the second half of 2011 and cushion gas injection started in June 2013. Located in a high topography and high tectonic stress region, the geological setting of the XGS field is structurally complex and highly faulted (Li et al., 2021). Because the field is located under a high topography structure (Fig 1), the magnitude and orientation of the in-situ stresses are greatly impacted. A comprehensive approach was used to capture the complexities in the stress model withing the XGS field. For this purpose, first the stress magnitudes and orientations are modeled using the wellbore scaled events from 14 main offset wells. These 1D well-centric models are then upscaled to the entire field using 3D static modeling approaches. Subsequently, a 4D numerical model is used to initialize the stresses to capture the impact of the complexities in geological structure and high topography changes in XGS field. Similar workflows were used to conduct 4D models by Fang et al. (2014) and Younessi et al. (2018).