Finite Element Optimised Back Analysis of In Situ Stress Field and Stability Analysis of Shaft Wall in the Underground Gas Storage

Abstract

A novel optimised back analysis method is proposed in this paper. The in situ stress field of an underground gas storage (UGS) reservoir in a Turkey salt cavern is analysed by the basic theory of elastic mechanics. A finite element method is implemented to optimise and approximate the objective function by systematically adjusting boundary loads. Optimising calculation is performed based on a novel method to reduce the error between measurement and calculation as much as possible. Compared with common back analysis methods such as regression method, the method proposed can further improve the calculation precision. By constructing a large circular geometric model, the effect of stress concentration is eliminated and a minimum difference between computed and measured stress can be guaranteed in the rectangular objective region. The efficiency of the proposed method is investigated and confirmed by its capability on restoring in situ stress field, which agrees well with experimental results. The characteristics of stress distribution of chosen UGS wells are obtained based on the back analysis results and by applying the corresponding fracture criterion, the shaft walls are proven safe.

An associated evaluation methodology of initial stress level of coal-rock masses in steeply inclined coal seams, Urumchi coal field, China

“…A reasonable evaluation of the initial stress field of the rockmass becomes very difficult due to all complicated factors. At present, the evaluation methodology for analyzing the initial stress field is mainly based on the in situ stress measurement, and few analytical models are used to construct the initial stress field (Ma et al, 2018;Chen et al, 2018;Wang et al, 2017a;Gao and Ge, 2016;Deng et al, 2017;Pei et al, 2019;Yan et al, 2016):…”