金沙向斜龙潭组“三史”模拟与煤层气富集规律

"Burial history, evolution history, and hydrocarbon-generating history" simulation and accumulation laws of CBM in Longtan Formation, Jinsha syncline, Northern Guizhou Province

为了明确上二叠统龙潭组成熟演化的经过和煤层气的富集规律,以黔北地区金沙向斜龙潭组煤层为研究对象,基于区域构造、地质演化史和XC-1井煤层测试数据,结合Easy%Ro模拟技术对XC-1井进行埋藏史恢复,分析了龙潭组受热演化史和生烃史,指出了金沙向斜龙潭组煤层气富集的主要控制因素,研究结果表明:①金沙向斜的煤层埋藏-受热-演化-生烃史主要划分为3个阶段,可简述为受到深成变质作用开始煤化至瘦煤,后叠加岩浆热变质作用演化至无烟煤,最后抬升冷却的过程。距今225~145 Ma是煤层气生烃高峰期;②金沙向斜煤层气保存条件整体较好;③金沙向斜煤层气的成藏经历了沉积深成变质快速生气期、抬升岩浆受热持续生气期、抬升定型保存期3个阶段的演化过程,其中,沉积深成变质快速生气期为煤层气富集的主要阶段;④沉积相以海陆交互相龙潭组的潟湖-泥炭沼泽亚相煤层发育最稳定,抬升定型保存期决定了煤层气的最终保存条件,向斜构造中的平缓构造带更有利于煤层气的保存。结论认为,该研究结果可为金沙向斜煤层气的开发提供依据。

In order to figure out the evolution history and accumulation laws of coalbed methane(CBM) in Longtan Formation, this study took the Upper Permian Longtan Formation, Jinsha syncline of northern Guizhou Province,as an example. Based on regional structure, geological evolution history, and test data, the burial history of XC-1 well was rebuilt by means of Easy%Ro simulation. Then, the thermal evolution and hydrocarbon-generating history of Longtan Formation were analyzed. Finally, the main factors affecting CBM accumulation were pointed out. Results show that(1) the burial, evolution, and hydrocarbon-generating history of coal strata can be mainly divided into 3 periods. In the first period, it was carbonized into lean coal under plutonic metamorphism. In the second period, combined with magma thermometamorphism, it was evolved into anthracite coal. And in the third period, it experienced uplift and cooling. CBM-generating peak was in 225-145 Ma;(2) CBM preservation conditions in this syncline are overall better;(3) reservoir-forming process of CBM in Jinsha syncline can be divided into 3 stages, i.e., the sedimentary plutonic metamorphism and fast CBM generation, the uplift and continuous CBM generation of magma under thermal effect, and the uplift, shape finalization, and preservation. Among which, one stage of sedimentary plutonic metamorphism and fast CBM generation is the main one for accumulation;and(4) from the point of sedimentary facies,coal strata in lagoon-peat swamp subfacies of continental-marine-alternating facies in Longtan Formation are developed most stably. However, the uplift, shape finalization, and preservation stage dominates final CBM preservation,and gentle structural belts are more favorable for CBM preservation.