Current Status and Challenges of Log Evaluation Technology for Coal-Rock Gas

To provide technical support for the exploration and development of coal-rock gas resources, and facilitate the achievement of the "carbon peaking and carbon neutrality" goals, this study systematically compares the reservoir characteristics of coal-rock gas in typical exploration areas and their differences from coalbed methane, summarizes the current status of coal-rock gas logging evaluation technology, outlines the challenges faced in coal-rock gas logging evaluation, and points out its future development directions. The research indicates that: ① Coal-rock gas reservoirs are characterized by high temperature and pressure, complex pore structures, strong heterogeneity, and coexistence of free gas and adsorbed gas. In the Benxi formation of the Ordos basin, free gas accounts for an average of 24.48%, while in the Xishanyao formation of the Junggar basin, free gas accounts for an average of 54.00%. ② Logging technology has achieved results in identifying coal structure, calculating industrial components, and evaluating adsorbed gas content. Continuous evaluation of coal structure can be achieved through conventional logging curves and electrical imaging data, while industrial component and gas content calculation models can be established using methods such as multiple regression and machine learning. ③ Coal-rock gas logging evaluation currently faces four core challenges: calibration and quantitative evaluation of free gas content, cleat identification and parameter characterization, permeability prediction under multiple pore structures, and evaluation of mechanical properties in coal-bearing strata. ④ Future breakthroughs in technological bottlenecks require innovative rock physics experimental methods and instruments, the construction of multiporosity space interpretation models, and the development of big data intelligent algorithms. The conclusion states that, as an important strategic alternative resource, coal-rock gas logging evaluation requires systematic technological innovation tailored to the uniqueness of the reservoir and the establishment of a comprehensive evaluation system to effectively address current evaluation challenges and support efficient resource exploration and development.