四川盆地綦江地区长兴组岩溶储层特征与油气成藏

Karst reservoirs and their reservoir-forming characteristics:An example from Changxing Formation,Qijiang area,Sichuan Basin

对于四川盆地上二叠统长兴组到下三叠统飞仙关组界面的性质一直都存在着争议。为了进一步明确长兴组顶部是否发育不整合岩溶作用,以野外、钻井、岩心等资料为研究对象,分析了川南广大台内地区长兴组储层情况,指出了大量的溶沟、溶缝、溶洞等岩溶证据,进一步证实长兴组顶部发育不整合面。研究结果表明:①长兴组与飞仙关组之间存在沉积间断,表现为短期暴露不整合,古岩溶储层发育;②不整合岩溶作用形成的溶洞、溶缝叠加裂缝改造,形成的裂缝溶洞系统是长兴组的主要储集空间,为裂缝—孔洞型储层;③綦江地区长兴组天然气成藏模式属于“下生上储”型,龙潭组烃源岩是长兴组天然气的主要来源,烃源岩优质,成藏条件优越。结论认为:①长兴组天然气高产、稳产井与层间断裂匹配明显,断裂和裂缝为长兴组主要的油气运移通道,沟通烃源岩,从而控制了油气富集高产;②长兴组不整合岩溶储层的发现拓展了綦江地区乃至整个四川盆地的油气勘探领域,为下一步油气勘探提供了方向。

For one interface between the Upper Permian Changxing Formation and the Lower Triassic Feixianguan Formation in Sichuan Basin,its property is still in dispute.In order to figure out whether unconformity karst develops at the top of Changxing Formation,the Changxing reservoirs in the extensive platform of southern basin were analyzed on the basis of drilling and core data.A great number of evidences on karst were pointed out,such as karren,dissolution fracture,and vug,which might further prove the development of unconformity surface at the top of Changxing Formation.Results show that(1)there is a hiatus between Changxing and Feixianguan formations,representing as exposed unconformity in a short time to resulting in developed paleokarst reservoirs;(2)the fracture-vug system composing of vugs and dissolution fractures induced by unconformity karstification and fracturing reworking,is the main reservoir space in the Changxing Formation,so this formation is a kind of fractured-vuggy reservoirs;and(3)for the Changxing Formation,Qijiang area,the reservoir forming assembly is featured by lower source rock and upper reservoir.As the main gas source,the source rock of Longtan Formation with high quality and better reservoir-forming conditions is favorable in this area.It is concluded,because most wells of Changxing Formation are featured by high yield and stable production,better matching with obvious interlayer fault,both faults and fractures become dominant migration pathway to connect with source rock,so as to result in hydrocarbon enrichment and high yield.What's more,the discovery on the unconformity karst of Changxing reservoirs may expand an exploration domain in Qijiang area and even Sichuan Basin,also indicating the next exploration direction.