川东北元坝地区长兴组油气藏成藏模式

Hydrocarbon Accumulation Mode of Changxing Formation in YB Area of Northeastern Sichuan Basin

元坝地区二叠系长兴组气藏是由生物礁滩相储层所形成的一个大型的构造-岩性圈闭气藏。对川东北元坝地区长兴组油气藏成藏模式进行了研究。研究表明,印支晚期,二叠系烃源岩埋深达到2500m,古地温达到100℃,烃源岩Ro(镜质体反射率)高于0.5%,进入生油门限,至燕山早期,随着地层深度加大和古地温的升高,烃源岩Ro达到1.25%,烃源岩达到生油高峰,形成古油藏;燕山中期,古油藏埋深达到4400多米,古地温达160℃,原油开始裂解成气,古油藏转化为天然气藏;燕山晚期构造运动对该地区改造少,作为盖层的三叠系膏盐岩仍然存在,气藏得以保存成藏。

The Permian Changxing Formation gas reservoir in YB Area is a large tectonic lithologic trap gas reservoir formed by reef-flat facies reservoirs.Study on the thermal evolution history and burial history of source rock shows that Indochina burial depth of Permian source rock reaches 500m,the paleotemperature reaches 100℃ and Ro is above 0.5% which is in oil window.In Early Yanshan Period,with depth and temperature increases,Ro reaches 1.25% source rock reaches oil-generating peak and formes ancient reservoir.When burial depth of ancient reservoir in middle Yanshan period is more than 4400m and the paleotemperature is 160℃,crude oil crackes into gas and ancient reservoir changes to natural gas reservoir.Mid-Yanshanian movement and late-tectogenesis have little affect little to transformation of this area,Triassic gypsum rock as caprock still exists and gas reservoir can be preserved.