黄陵矿区一号煤矿中侏罗统延安组2号煤层“三史”演化过程单井数值模拟

Single Well Numerical Simulation of Middle JurassicYan’an Formation Coal No.2 Buried,Thermal and Hydrocarbon Generation History Evolution Process in Coalmine No.1,Huangling Mining Area

研究煤系烃源岩的生排烃阶段、生烃潜力及煤层气的成藏演化特征,需要对煤层的“三史”(即埋藏史、受热演化史和生烃史)演化过程进行恢复模拟研究。根据地层岩性、剩余地层现今埋深、地层孔隙度和镜质组反射率等数据或地质资料,运用PetroMod 1D模拟软件对黄陵矿区一号煤矿中侏罗世以来的三史演化过程进行重建。结果表明:黄陵矿区一号煤矿侏罗系含煤地层属于“早期沉降、晚期抬升”型,共经历了二次“沉降-抬升”阶段;第一次“沉降-抬升”发生在中侏罗世至古新世阶段,煤系地层埋深先快速增加(至侏罗纪末)后缓慢增加(至白垩纪末),最大埋深达1576m,古新世,地壳抬升剥蚀190m;中侏罗世至早白垩世初,煤岩受热温度及镜质组反射率“先缓慢后快速再缓慢”增加,至晚白垩世末,发生差异分化,2号煤层下底部煤岩受热温度79~126℃,镜质组反射率从0.50%演化至0.79%,2号煤层上顶部煤岩受热温度78~108℃,镜质组反射率从0.50%演化至0.67%(古新世),煤岩受热温度降低,煤化作用停止;第二次“沉降-抬升”发生在始新世至今阶段,煤系地层先沉降100m,之后以地层85.4m/Ma速率发生最大抬升,煤层受热温度进一步降低至现今22℃,煤有机质热解生烃作用(热成因气)停止,但微生物降解有机质生烃作用(次生生物成因气)正在进行。

To study coal measures source rock hydrocarbon generation and expulsion stages,hydrocarbon generation potential and coalbed methane reservoiring evolution features have to carry out recovery simulation study on coal seam“three histories”(i.e.buried history,thermal evolution history and hydrocarbon generation history)evolution process.According to strata lithologic characters,residual strata buried depths today,porosity and vitrinite reflectance etc data or geological information,using PetroMod 1D simulation software carried out reestablishment of“three histories”evolution process in the coalmine No.1,Huangling mining area.The result has shown that the Jurassic coal-bearing strata in the coalmine belong to“early stage subsidence,later stage uplift”type,and experienced two“subsidence-uplift”stages.The first“subsidence-uplift”stage happened during middle Jurassic up to Paleocene,buried depth of coal measures strata fast increasing first(up to the end of Jurassic),then tardily increasing(up to the end of Cretaceous),with maximum depth 1576m,during Paleocene,crust uplift and denuded 190m;during middle Jurassic to earlier early Cretaceous,coal and rock heating temperature and vitrinite reflectance“tardily first then fast and then tardily”increasing.Up to the end of Cretaceous,differential differentiation had been happed,coal No.2 bottom coal and rock heating temperature 79℃~126℃,vitrinite reflectance from 0.50%evolved to 0.70%,coal No.2 top coal and rock heating temperature 78℃~108℃,vitrinite reflectance from 0.50%evolved to 0.67%;during Paleocene,coal and rock heating temperature lowering down,coalification stopped.The second“subsidence-uplift”stage happened during Eocene up to present,coal measures strata subsidence 100m first,then happened maximum uplift under 85.4m/Ma rate,coal heating temperature further lowering down up to present 22℃.Coal organic matter pyrogenic decomposition hydrocarbon generation(thermogenic gas)has stopped,but microbiological deterioration organic matter hydrocarbon generation(secondary biogenic gas)is underway.