Tectonic evolution revealed by thermo-kinematic and its effect on shale gas preservation

Abstract

This study provides new insight for kinematic restoration in the thrust nappe and the effect of tectonic evolution on shale gas preservation was demonstrated in a case study from the Dingshan area in the southeastern Sichuan Basin, southwest China. The uplift process was reconstructed by sandbox experiment, discrete element method, vitrinite reflectance and thermochronology data, including apatite fission track, apatite (U–Th)/He and zircon (U–Th)/He. Thermo-kinematic analysis indicated that from southeast to northwest, the initial uplift time was getting earlier and the erosion increased, while the horizontal displacement decreased during the Alpine stage (Early Cretaceous-Eocene). During the Himalayan stage (Eocene-present time), it was characterized with rapid uplift as a whole. To study dynamic evaluation of shale gas preservation during tectonic evolution, the temperature and pressure evolution were revealed combining fluid inclusion analysis and basin modeling and variation in shale gas content was quantified. Differential uplift caused obvious differences in the process of cooling, pressure decreasing, fracturing and shale gas losing. With moderate uplift (∼3350–3550 m), a few fractures generated in the shale and roof and few gas (∼0.95–1.72 m3/t) diffused laterally. Enormous uplift (∼5350 m) resulted in obvious fractures and massive gas loss (∼3.22 m3/t) by lateral diffusion and vertical dissipation.