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Renewable and environmentally friendly energy sources, such as hot dry rocks (HDR) geothermal reservoirs, have gained significant attention for electricity generation. The enhanced geothermal system (EGS) is also being explored in conjunction with HDR. Geophysical techniques have been employed to characterize the geological properties of these reservoirs at various scales. Local geological analysis requires small-scale geophysical data to provide essential information for HDR modeling. Located in the northeast margin of the Qinghai-Tibet Plateau, Gonghe basin has emerged as a potential area for HDR exploration due to its high geothermal gradient, elevated heat flow, and extensive distribution of igneous rocks, particularly in the Gonghe town (Qiabuqia) and surrounding areas. Gravity and magnetic surveys were conducted in this region. To gain a comprehensive understanding of the spatial and vertical distribution of HDR, the gravity and magnetic data were processed using 2D manual inversion and 3D cross-gradient joint inversion, employing the smooth l0 norm constraint of minimum support functional stabilizer. The 2D model revealed the presence of a sedimentary cap with a thickness ranging from approximately 1000 to 1500 m. Various periods of granites and associated intrusive processes were widely dispersed, underlying the sediments along with deep fault zones. Regarding HDR delineation, the 3D models indicated a prospective area encompassing Gonghe town and Dongba. The density and susceptibility values were estimated to be over 2.6 g/cm3 and 4×10−3 SI, respectively, based on the existing HDR distribution observed along the geological profile of DR4-QR1-DR3-DR2 wells. The upper boundary of the HDR reservoir was delineated at a depth of approximately 2000 m, with a total volume estimated at around 6,100 km3 above a depth of 3, 500 m. The density and susceptibility models were influenced by lithology, stress conditions, and hydrothermal alteration. During the HDR exploitation phase, more precise geophysical methods such as microgravity, seismic, and magnetotelluric (MT) surveys would be more applicable for accurate characterisation.
Zhao et al. (Tue,) studied this question.