Coupled thermal−gas−mechanical (TGM) model of tight sandstone gas wells

Abstract

The mechanism of CO2 fracturing under coupled thermal−gas−mechanical (TGM) conditions is important for gas production in tight sandstone gas wells. In this study, a coupled TGM model was proposed on the basis of the elastic damage principal, and the coupling relationships were expressed by the governing equations. The proposed model was then tested through comparison between the numerical uniaxial compressive test and the laboratory test. COMSOL MULTIPHYSICS was adopted to calculate the coupled numerical model; the impact of injection rate and injection gas temperature was fully investigated. The research results showed that the initiation pressure stayed stable with the increase of the breakdown pressure and injection rate over a certain range (0.106 m3 s−1–0.848 m3 s−1). The seepage area under the injection rate of 0.848 m3 s−1 was 3.45 times that under the injection rate of 0.106 m3 s−1, which resulted from the gradual destruction of the samples and the formation of new fractures at higher injection rate. The initiation pressure and the breakdown pressure decreased, since tensile cracks tended to form with the increase of injection temperature. Shear cracks formed around the hole—the crush area. The tensile cracks propagated much deeper into the surrounding rock under the higher injection temperature. This research provides a study of unconventional oil and gas extraction for reference.