Increasing Shale Gas Recovery through Thermal Stimulation: Analysis and an Experimental Study

Abstract

Abstract The Silurian Longmaxi shale gas play in the Jiaoshiba (JSB) structure in the southeast margin of the Sichuan Basin in China is studied to discuss the key factors that control the adsorption/desorption behavior of natural gas in shale formations. The rationale for this study is that understanding these factors can be helpful in shale gas stimulation designs that enhance recovery by combining hydraulic fracturing with thermally induced desorption of adsorbed shale gas. The Jiaoshiba structure is a faulted anticline which experienced multiphase tectonic movement. The Longmaxi Formation has high thermal evolution degree with Ro more than 2.2%, and has a 35-45 meters thick high-quality shale (TOC > 2%) in its lower part. The reservoir is overpressure with a pressure coefficient of 1.55, and shale gas production and pressure are stable. Experimental measurements have indicated that more than 65% of the total gas storage in the Jiaoshiba shales exists as an adsorbed phase. Modeling the adsorbed phase can impact the selection of stimulation techniques as well as production forecasts. Adsorption generally cannot be determined accurately from history matching production data alone. The laboratory testing of actual shale samples from reservoir cores is important for characterizing shale gas adsorption behavior. Previous laboratory studies have reported data from measurements at single temperatures, and the measured data have been represented by Langmuir isotherms. However, the effect of temperature on adsorption has not been explored. In this work, a series of experiments were conducted to measure adsorption curves for shale samples at various temperatures and depths from the Jiaoshiba shales. We investigated the representation of adsorption behavior as a function of both temperature and pressure. The pressure-temperature dependent gas adsorption behavior is described by Bi-Langmuir model by fitting the unknown adsorption characteristic parameters against laboratory experiment data at low temperature, the gas adsorption behavior at higher temperature can be predicted by extrapolation from the model. The predicted gas adsorption capacity agree well with our experiment data, which demonstrate this model's capability to predict gas adsorption capacity at reservoir temperature based on data measured at laboratory conditions. The pressure and temperature sensitive gas adsorption behavior is incorporated into an unconventional reservoir simulator, to investigate how thermal stimulation can impact shale gas production and ultimate recovery from hydraulic fractured shale formations. The results indicates that thermal stimulation has the potential to enhance shale gas recovery significantly by altering shale gas adsorption/desorption behavior through the elevation of formation temperature.