Production prediction method of horizontal wells in tight gas reservoirs considering threshold pressure gradient and stress sensitivity

Abstract

This study is aimed at the problem of specific seepage mechanisms, such as the threshold pressure gradient and stress sensitivity, in tight gas reservoirs, which have a tremendous influence on a gas well production prediction. Based on the dual-porosity seepage theory of the horizontal wells in tight gas reservoirs, a seepage model is established considering the two mechanisms of stress sensitivity and threshold pressure gradient comprehensively, adopting a circular closed formation as the research object. Subsequently, the production prediction model is obtained by combining the perturbation theory, the Sturm–Liouville eigenvalue theory, an orthogonal transformation, and a point source function. This production model is proved to be reliable based on analysis of the production data of the Sulige gas field. The sensitivity analysis of the parameters shows that the increasing curves of the production reduction range and both the above-mentioned mechanisms are parabolic. When the threshold pressure gradient and stress sensitivity are considered separately, the production is reduced by 16.67% and 15.0%, respectively. If both the mechanisms are considered simultaneously, the production is reduced by 30.83%. Therefore, the threshold pressure gradient or stress sensitivity must be considered in tight gas reservoirs; otherwise, it will cause a significant deviation when predicting the initial production of a horizontal well, which can affect the decision-making.