川南煤田古叙矿区龙潭组煤层受热-生烃史及气体成因

Heat-hydrocarbon generating history and gas origin of Longtan Formation in Guxu mining area in South Sichuan coalfield

为了明确川南煤田古叙矿区龙潭组煤层成熟演化过程及气体成因类型,运用Petromod 1D模拟软件,结合川南煤田古叙矿区岩性地层分布、煤层埋深、泥岩声波时差、包裹体均一温度、气体稳定碳同位素组成测试等数据,对川南煤田古叙矿区C 17号煤层的埋藏史、受热史和有机质成熟生烃史进行重建。结果表明川南煤田古叙矿区地层自晚二叠世沉积以来,地层经历了不同程度的剥蚀,即下三叠统嘉陵江组的剥蚀厚度约为39 m、上侏罗统与上覆地层的剥蚀厚度约为314 m,下白垩统与上覆地层的剥蚀厚度约为2600 m、下古新统与上覆地层的剥蚀厚度约为1681 m;龙潭组C 17号煤层自晚二叠世沉积以来,主要经历了3次“沉降-抬升”过程,最大埋深为晚白垩世末期的5101 m,遭受最高受热温度为早白垩世末的234℃,现今温度为47℃,煤有机质成熟生烃过程分为未成熟、成熟生油、高成熟生湿气、过成熟生干气和生烃枯竭5个阶段。煤层气为一期成藏且发生散失时间为中侏罗世,富集时间为早白垩世。现今龙潭组C 17号煤层中赋存气体成因类型为热成因气。

In order to clarify the maturation evolution process and gas genesis type of coal seam of Longtan Formation in the Guxu mining of south Sichuan coalfield,the burial history,heating history and mature hydrocarbon generation history of organic matter of No.2 coal seam in Guxu mining area was studied in the paper using the method of Petromod 1D simulation software,in light of the date of rock formation distribution,coal seam depth,mudstone sonic log interval,homogenization temperature of the inclusions,gas stable carbon isotopic composition test,etc.The results show that strata have experienced different degrees of denudation since the late Permian deposition in Guxu mining area.Namely,the denudation thickness of lower Triassic Jialingjiang formation is about 39 m,the denudation thickness of upper Jurassic and the overlying is about 314 m,the denudation thickness of lower Cretaceous and the overlying strata is about 2600 m,the denudation thickness of lower Palaeocene and the overlying strata is about 1681 m.The coal seam No.C 17 of Longtan Formation has undergone three“subsidion-lifting”processes since the deposition of the Late Permian.The maximum burial depth was 5101 m at the end of the late Cretaceous,and the maximum heating temperature was 234℃at the end of the Early Cretaceous.The current temperature is 47℃.The mature hydrocarbons generation process of coal organic matter can be divided into five stages:immature,mature oil generation,high mature moisture generation,over-mature dry gas generation and hydrocarbon depletion.The coal-bed methane is the first stage of accumulationand and dissipated in the middle Jurassic.The accumulation time is early Cretaceous.Today,the genetic type of gas in C 17 coal seam of Longtan Formation is thermal gas.