Abstract: Coalbed methane, as a new unconventional gas resource, has achieved significant exploration breakthroughs in central and western basins of China during recent years. Elucidating the hydrocarbon generation capacity of Jurassic coals in Turpan-Hami Basin is crucial for assessing their resource potential and guiding the exploration and development of coalbed methane. Coal samples were collected from the Jurassic Badaowan and Xishanyao formations in Turpan-Hami Basin. Following the analyses of macerals (vitrinite, inertinite, and exinite) and mineral contents, hydrocarbon generation simulation experiments were conducted using a gold-tube system. Based on the hydrocarbon yield data per unit mass of pure coal at varying temperatures, equations for gas and oil generation were established with the contents of vitrinite, inertinite, and exinite as independent variables. By solving the equations, the contributions of different macerals to hydrocarbon generation at varying temperatures were quantitatively calculated. The results show as follows. (1) Significant variations in hydrocarbon generation potential of coals between the Badaowan and Xishanyao formations in Turpan-Hami Basin are primarily controlled by coal-accumulation environment, organic matter type and maturity. Badaowan Formation, dominated by hydrogen-rich Type Ⅱ organic matter, exhibits strong oil generation potential, whereas Xishanyao Formation is dominated by Type Ⅲ humic organic matter, exhibiting relatively greater gas generation potential. Nevertheless, the overall low maturity of Xishanyao Formation limits effective hydrocarbon generation and expulsion. (2) Exinite serves as the primary oil-prone maceral in both formations, achieving maximum oil-generation yields of 543.87-566.15 mg/g. In contrast, the maximum oil yields from vitrinite are only 23.55-30.04 mg/g, while inertinite exhibits negligible oil-generating potential. Termination of gas generation occurs when the vitrinite reflectivity (R_o) is equal to 5.15 %, and the yields of hydrocarbon gas from vitrinite, liptinite, and inertinite are 189.70-190.40 cm³/g, 283.20-303.00 cm³/g, and 12.80-13.40 cm³/g, respectively. (3) The oil-gas ratio (OGR) of coal displays an M-type evolutionary profile with increasing thermal maturity, manifesting the phased dynamic equilibrium between primary oil-gas generation and crude oil cracking. (4) Vitrinite dominates hydrocarbon generation (contributing the most significantly to the gas generation of 89.52%-93.89%) in both formations, while exinite serves as the vital oil-generating maceral and accounts for 39.42%-55.48 % of total oil yield. (5) Based on the evolution characteristics of hydrocarbon generation, it is concluded that for conventional humic coal, gas yield is relatively low when R_o<0.8 %, leading to a great difficulty in the formation of large-scale thermogenic gas accumulations. Therefore, at R_o<0.8 %, exploration should prioritize biogenic and mixed-source gas, whereas at R_o>1.0 %, thermogenic coalbed methane becomes the primary target.

Key words: coal maceral, thermal simulation experiment, hydrocarbon generation capacity, vitrinite, inertinite, exinite, Turpan-Hami Basin, Jurassic Badaowan Formation, Jurassic Xishanyao Formation

摘要： 近年来,中国中西部盆地的煤层气勘探开发取得了重大突破,阐明吐哈盆地侏罗系煤岩的生烃能力,对评价煤层气资源潜力、指导煤层气勘探开发具有重要意义。基于吐哈盆地侏罗系八道湾组和西山窑组煤样品,开展了有机显微组分(镜质组、惰质组、壳质组)和矿物含量分析;采用黄金管装置进行了生烃热模拟实验;根据不同温度下单位质量纯煤的生烃实验数据,建立了以镜质组、惰质组和壳质组含量为自变量的生气与生油方程;通过求解方程组,定量计算了各有机显微组分在不同温度下的生烃贡献。研究结果表明:①吐哈盆地八道湾组和西山窑组煤的生烃潜力差异显著,受聚煤环境、有机质类型和成熟度共同控制,八道湾组煤的有机质类型以富氢Ⅱ型为主,生油潜力较为突出,西山窑组煤的有机质类型则以Ⅲ型腐殖质为主,产气潜力相对更高,但整体处于低成熟阶段制约了其有效排烃。②2套煤中的壳质组为生油主力,其生油量为543.87~566.15 mg/g,镜质组的生油量为23.55~30.04 mg/g,惰质组基本不具备生油能力;镜质体反射率(R_o)为5.15%时,煤达到生气终点,镜质组、壳质组、惰质组所生成的烃类气体量分别为189.70~190.40 cm³/g、283.20~303.00 cm³/g和12.80~13.40 cm³/g。③煤岩的油气比随成熟度的增加呈"M"型演化特征,可直观地反映油气生成与原油裂解过程的阶段性动态平衡。④2套煤岩均以镜质组为主要生烃组分,其对烃类气生成的贡献最为显著,贡献率达89.52%~93.89%;壳质组则是重要的生油组分,其生油贡献率为39.42%~55.48%。⑤结合生烃演化特征分析认为,当煤的R_o＜0.80%时,常规腐殖煤的烃类气生成量较低,形成大规模热成因气藏的难度大,勘探应以生物气及混源气为主,而当煤的R_o＞1.00%时,应以热成因煤层气为勘探重点。

关键词: 煤岩显微组分, 热模拟实验, 生烃能力, 镜质组, 惰质组, 壳质组, 吐哈盆地, 侏罗系八道湾组, 侏罗系西山窑组