Geomechanical risk and mechanism analysis of CO_(2) sequestration in unconventional coal seams and shale gas reservoirs

With global greenhouse gas emissions hitting record highs in 2021,CO_(2) geological sequestration(CGS)is the most realistic and feasible technology to ensure large-scale carbon reduction to achieve global carbon capping and carbon neutrality goals.Both coalbed methane and shale gas have the characteristics of self-generation and selfstorage,which is considered to be a valuable target reservoir for geological sequestration of CO_(2).After a high volume of CO_(2) is injected into unconventional coal seams and shale gas reservoirs,many geomechanical issues may be induced,resulting in leakage.Therefore,it is crucial to evaluate the geomechanical risks of CO_(2) geological sequestration.In this article,global CO_(2) emissions and geological resources available for sequestration are teased out.The effects of coupled CO_(2)-water-rock-driven geomechanical,geophysical,and geochemical interactions on the evolution of rock physical properties and pore characteristics,as well as caprock sealing,are discussed.The caprock failure and its inducing mechanism are analyzed,and the criteria for predicting the occurrence of risk are summarized,which is necessary for pressure management and risk prevention.To serve as a benchmark for CO_(2) sequestration in unconventional coal seams and shale gas reservoirs.

Influence of channel/back-barrier thickness on the breakdown of AlGaN/GaN MIS-HEMTs

The leakage current and breakdown voltage of AlGaN/GaN/AlGaN high electron mobility transistors on silicon with different GaN channel thicknesses were investigated.The results showed that a thin GaN channel was beneficial for obtaining a high breakdown voltage,based on the leakage current path and the acceptor traps in the AlGaN back-barrier.The breakdown voltage of the device with an 800 nm-thick GaN channel was 926 V@1 m A/mm,and the leakage current increased slowly between 300 and 800 V.Besides,the raising conduction band edge of the GaN channel by the AlGaN back-barrier lead to little degradation for sheet 2-D electron gas density,especially,in the thin GaN channel.The transfer and output characteristics were not obviously deteriorated for the samples with different GaN channel thickness.Through optimizing the GaN channel thickness and designing the Al GaN back-barrier,the lower leakage current and higher breakdown voltage would be possible.