Calculation of free gas saturation in deep coal seams in the Kezilenuer Formation
BIE Kang1,2,3, CAI Tian4, XIN Yi1,2,3, LIU Yue-Jiao4, HAN Chuang1,2,3, SUN Jian-Meng4()
1. Tarim Oilfield Company, PetroChina, Korla 841000, China 2. R&D Center for Ultra-Deep Complex Reservoir Exploration and Development, CNPC, Korla 841000, China 3. Engineering Research Center of Ultra-deep Complex Oil and Gas Reservoir Exploration and Development, Xinjiang Uygur Autonomous Region, Korla 841000, China 4. School of Geosciences, China University of Petroleum (East China), Qingdao 266000, China
Compared to shallow coal seams, deep coal seams have gradually transitioned into a complex geologic environment characterized by high temperatures, pressures, and in situ stresses, and low permeability. Temperature and other conditions result in enhanced negative adsorption effects, leading to free gas production. Free gas saturation serves as a typical parameter for predicting reserves and guiding the optimal design of production and drainage plans, rendering its accurate determination highly significant. This study investigated the coalbed methane in the Jurassic Kezilenuer Formation in the tectonic zone north of the Kuqa depression within the Tarim Basin. It calculated the free gas saturation in the target layer based on adsorption isotherms, field analysis, inversion, the element-modified bulk modulus method, and the Archie, Gassmann-Wood, and Gassmann-Brie equations. Furthermore, it comparatively analyzed the results derived from these calculation methods combined with two-dimensional nuclear magnetic resonance data. The results indicate that the element-modified bulk modulus method and the Gassmann-Wood and Gassmann-Brie equations are more appropriate calculation methods for the study area. Overall, the results of this study provide a valuable reference for calculating free gas saturation in deep coal seams in the study area, further guiding and advancing the exploration and production of deep coalbed methane.
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