关键词: 富油煤, 分布特征, 形成机制, 主控因素, 储量估算, 基础地质—原位热解工程一体化

Abstract: Tar-rich coal is a strategically important unconventional hydrocarbon resource in China, and the study of its formation mechanisms and exploitation potential plays a pivotal role in national energy transition. Through systematically analyzing the geological characteristics and genetic mechanisms of major tar-rich coal basins in China, it has been found that tar yield is controlled by the coupled effects of multiple factors. Tar-rich coals were predominantly developed in the Ordos, Junggar, Turpan-Hami, and Santanghu basins from the Paleozoic to the Mesozoic, especially in the Jurassic. Research demonstrates that tar-rich coal is predominantly composed of vitrinite, characterized with ultra-low to medium moisture and ash contents, ultra-low to medium sulfur content, medium-high to high volatile matter, and significant variations in tar yield. It exhibits the following petrographic characteristics: vitrinite content ranging from 30.10 % to 82.99 %, inertinite from 15.38 % to 66.53 %, liptinite from 0.77 % to 4.20 %, and tar yields varying between 4.39 % and 14.58 % (peaking at 22.80 %). Moreover, it shows the following coal quality characteristics: moisture content ranging from 2.82 % to 11.47 %, ash content from 8.59 % to 22.40 %, total sulfur content from 0.33 % to 1.31 %, and volatile matter content from 33.12 % to 46.14 %. In China, a majority of tar-rich coals contain Type Ⅲ₁ kerogen derived mainly from woody and herbaceous plants, with minor contributions from aquatic plants and lower algae. The tar yield is primarily determined by several key factors, including the content of hydrogen-rich vitrinite, types of coal-forming plants, coal molecular structure, thermal maturity of organic matter, and sedimentary environment. For coals with similar ranks, variations in tar yield essentially result from the dynamic changes in organic molecular structures with the increase of thermal evolution degree, which is specifically manifested at the molecular level as the dynamic evolution of hydrogen-rich and oxygen-containing functional groups. In terms of sedimentary environments, tar-rich coals are predominantly developed in the reservoirs of delta plain subfacies and shore/shallow lacustrine subfacies, and the shallow-water environment characterized with weak hydrodynamics and low salinity is most conductive to high tar yields. It is predicted that the tar-rich coals at depths less than 2 000 m in Santanghu Basin, Turpan Basin, Hami Basin and Ordos Basin amount to over 250 billion tons. Among these, two key sweet spots have been identified, i.e., the Jurassic reservoirs in northern Shaanxi region of Ordos Basin, with 124.26 billion tons of tar resources and the Santanghu Basin. To overcome the current bottlenecks in tar-rich coal development, the study proposes a geology-engineering integration model that combines multi-index oil potential assessment with multi-field coupled pyrolysis simulation for precisely locating in-situ pyrolysis targets. These findings provide both the scientific framework and technical approach for low-carbon utilization of tar-rich coal resources, which is of strategic significance for facilitating the transition of coal from fuels to chemical feedstocks.

Key words: tar-rich coal, distribution characteristics, formation mechanism, main controlling factors, reserve estimation, integration of basic geology and in-situ pyrolysis engineering