川西南段大邑地区深层碳酸盐岩油气成藏探讨

Discussion on Hydrocarbon Accumulation of Deep Carbonate Rocks in Dayi Area of Southwest Sichuan

川西南段大邑地区所处的区域,其深层处于勘探的空白区,深入探讨该区海相油气成藏条件,不但能更新该区构造地质认识,也能为川西深层下一步油气勘探提供理论。基于研究区及周边钻井岩心、岩屑及地震等资料,对川西南段大邑地区深层油气地质条件进行综合分析。研究结果表明:①川西南段地层剥蚀至下寒武统筇竹寺组黑色泥页岩,该套烃源层广泛分布,为成藏提供了物质基础;②大邑深层发育多套储层,包括灯影组白云岩、栖霞组和茅口组白云岩、峨眉山玄武岩组玄武岩、嘉陵江组与雷口坡组白云岩,露头和探井都显示具有良好的储集条件;③纵向上发育中-下三叠统膏盐岩和巨厚的陆相碎屑岩盖层,具有很好的封挡条件。野外露头及钻井岩心中普遍可见储层大量沥青,说明形成过古油藏;④桐湾运动和加里东运动形成的不整合面在研究区叠加形成优质输导体系,加之大邑背斜带形成的有利纵向沟源断裂输导体系。大邑构造带古圈闭保持完整,与油气运移相匹配,有利于天然气的保藏,是未来深层天然气有利的潜在勘探区。

The Dayi area in the southwest part of Sichuan is a blank area for exploration.The deep exploration of Marine oil and gas accumulation conditions in this area can not only update the structural geological understanding of this area,but also provide the theory for further oil and gas exploration in the deep west part of Sichuan.Based on drilling core,cuttings and seismic data in and around the study area,the deep oil and gas geological conditions in Dayi area of southwest Sichuan Section were comprehensively analyzed.The results show these as follows.The strata in southwest Sichuan are denudated to the black shale of the Early Cambrian Qiongzhusi Formation,which is widely distributed and provided the material foundation for hydrocarbon accumulation.Several reservoirs are developed in deep Dayi,including dolomite of Dengying Formation,dolomite of Qixia and Maokou Formation,basalt of E-mei Mountain Formation,dolomite of Jialingjiang Formation and Leikoupo Formation.Outcrops and exploration Wells all show good reservoir conditions.The Middle and Lower Triassic gypsum rock and the very thick continental clastic rock cap are developed longitudinally with good sealing conditions.A large amount of bitumen is commonly found in outcrops and drilling cores,indicating the formation of paleo-oil reservoirs.The unconformity surface formed by Tongwan movement and Caledonian movement overlaps in the study area to form a high-quality transport system,and the favorable longitudinal gully source fault transport system formed by Dayi anticline belt.The paleotrap of Dayi structural belt is intact,which matches with oil and gas migration,is conducive to the preservation of natural gas,and is a favorable potential exploration area for deep natural gas in the future.