鄂尔多斯盆地东缘本溪组8#煤层方解石脉体成因

Genesis of Calcite Veins in 8#Coal Bed of Benxi Formation on Eastern Margin of Ordos Basin

针对鄂尔多斯盆地东缘本溪组8#煤层方解石脉体成因不清的问题,综合运用显微岩相学、同位素地球化学和流体包裹体等方法,开展方解石脉发育期次分析以明确成脉流体来源和形成时间。研究结果表明,研究区8#煤层中发育2期方解石脉体(C1和C2),C1方解石脉的成岩流体主要为源于围岩母岩的地层卤水和富生物气有机流体,C2方解石脉的流体来源主要与有机质脱羧作用形成的液态烃类流体有关,同时C1和C2方解石脉的形成均受到早白垩世构造热事件导致的深部热液流体影响。结合研究区烃类成藏史和埋藏史分析,明确C1方解石脉的形成时间在晚三叠世-早侏罗世期间,C2脉体形成时间为晚侏罗世-早白垩世。结合研究区8#煤层勘探生产实践,方解石脉发育区域煤层气富集程度较高,具有良好的勘探开发前景。研究成果对于煤层气富集区域的勘探具有重要的参考意义。

In view of the unclear genesis of calcite veins in 8#Coal Bed of Benxi Formation on Eastern Margin of Ordos Basin,the calcite vein development stages were analyzed to determine the source and formation time of vein-forming fluids by micro petrography,isotope geochemistry,fluid inclusion and other methods.The study results indicated that calcite veins(C1 and C2)in Stage 2 were developed in 8#coalbed in the study area,the diagenetic fluids of C1 calcite veins were mainly stratigraphic brine and biogas-rich organic fluids from surrounding rock and parent rock,the diagenetic fluids of C2 calcite veins were mainly liquid hydrocarbon fluids formed by the decarboxylation of organic matter,and meanwhile the formation of C1 and C2 calcite veins was affected by deep hydrothermal fluid formed by Early Cretaceous tectonic thermal events.Combined with the analysis of the hydrocarbon formation and burial history in the study area,it was clear that C1 calcite veins were formed from Late Triassic to Early Jurassic and C2 veins were formed from Late Jurassic to Early Cretaceous.Production of 8#coalbed in the study area,the calcite vein development area had a high degree of CBM enrichment,indicating bright prospects for exploration and development.The study results provide an important reference for the exploration of CBM-rich areas.