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

摘要： 富油煤作为中国重要的非常规油气资源,研究其形成机制与开发潜力对国家能源结构转型具有重要意义。通过梳理中国主要富油煤盆地的地质特征与形成机制,揭示了多因素耦合控制下富油煤的焦油产率。中国富油煤主要分布在鄂尔多斯盆地、准噶尔盆地、吐哈盆地和三塘湖盆地等,形成时代贯穿古生代—中生代,主要在侏罗纪。研究结果表明,中国富油煤整体呈现出以镜质组为主,具有特低—中等水分含量、特低—中等灰分含量、特低—中等硫含量、中高—高挥发分以及焦油产率差异显著的特征。富油煤的煤岩特征表现为:镜质组含量为30.10%~82.99%,惰质组含量为15.38%~66.53%,壳质组含量为0.77%~4.20%,焦油产率为4.39%~14.58%(局部最高可达22.80%)。富油煤的煤质特征表现为:水分含量为2.82%~11.47%,灰分含量为8.59%~22.40%,全硫含量为0.33%~1.31%,挥发分含量为33.12%~46.14%。中国富油煤的干酪根类型多为Ⅲ₁型,成煤植物多以木本—草本植物为主,水生植物与低等藻类次之。富油煤的焦油产率受控于富氢镜质体含量、成煤植物类型、煤分子结构、有机质热演化程度以及沉积环境等因素。在相近的煤阶条件下,控制富油煤焦油产率的核心实质上是有机质分子结构跟随热演化程度的动态响应过程,在分子结构上具体表现为富氢基团与含氧基团的动态演化。在沉积环境方面,中国富油煤多发育在三角洲平原亚相与滨/浅湖亚相,浅覆水、微流动、低盐度的水体环境最利于高焦油的产出。三塘湖盆地、吐哈盆地、鄂尔多斯盆地2 000 m以浅富油煤的总资源量预测超过2 500×10⁸t,其中,鄂尔多斯盆地陕北地区侏罗系(其焦油资源量为124.26×10⁸t)与三塘湖盆地为两大富油煤核心富集区。针对目前富油煤的开发瓶颈,建议构建地质—工程一体化模型,整合多指标含油性评价与多场耦合热解模拟,实现原位热解靶区的精准定位。研究结果为富油煤资源的低碳开发提供了理论框架与技术路径,对推动煤炭从燃料向原料转型具有一定的战略价值。

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