四川盆地中部地区海相储层煤成气来源

Sources of coal-derived gas in marine strata in central Sichuan

四川盆地中部地区(川中地区)海相的三叠系雷口坡组、嘉陵江组、飞仙关组及二叠系长兴组都发育有气藏,多年来对于这些气藏中天然气的来源仍有较大分歧,特别是雷口坡组气藏,气源具体来自哪一套烃源岩仍不明朗。采用天然气地球化学研究方法,结合地质背景对川中地区二叠系和三叠系气藏天然气进行组分和同位素对比研究,认为雷口坡组四段天然气有不少样品为煤成气,天然气来自上覆须家河组烃源岩,还有部分天然气来自下伏雷口坡组烃源岩;雷口坡组一段和嘉陵江组天然气与长兴组、飞仙关组天然气同源。在龙岗地区,长兴组、飞仙关组天然气主要来自下伏龙潭组煤系烃源岩。在磨溪气田龙潭组在一些地区可能相变为吴家坪组,以腐泥型有机质为主,生成的天然气为油型气,相应的上覆长兴组、飞仙关组、嘉陵江组和雷一段储集层中的天然气为油型气。

There are gas reservoirs in the Triassic Leikoupo Formation,Jialingjiang Formation,Feixianguan Formation and Permian Changxing Formation in the marine strata of the central Sichuan Basin.Over the years,the gas sources in these gas reservoirs,especially the gas source of the Leikoupo Formation are still unclear.In this paper,the natural gas geochemistry,combined with geological background,are used to compare the composition and isotopes of natural gas in the Permian and Triassic gas reservoirs in the central Sichuan Basin.It is believed that many samples of the 4th member of Leikoupo Formation are coal-derived gas,and the natural gas comes from the overburden Xujiahe Formation source rock,and there is also some other natural gas from the Lower Leikoupo Formation source rock.The gas of the 1st member of Leikoupo and Jialingjiang Formation is homologous to the natural gas of Changxing and Feixianguan formations.In Longgang Gas Field,the natural gas of the Changxing and Feixianguan formations mainly comes from the coal-bearing source rocks of the Longtan Formation.In the Moxi Gas Field,the Longtan Formation may be transformed into the Wujiaping Formation in some areas,which is mainly composed of sapropelic organic matter,and the natural gas produced is oil-type gas.Gases from the corresponding overlying reservoirs of Changxing,Feixianguan and Jialingjiang formations,and also the 1st member of Leikoupo Formation are coal-derived gas.