渤中凹陷碳酸盐岩潜山岩溶分带特征与优质储层分布规律研究

Distribution Pattern of High-quality Reservoirs and Karst Zoning Feature of Carbonate Rocks in Buried Hills:A Case Study from the Bozhong Sag,Bohai Bay Basin,China

渤海湾盆地渤中凹陷西南环古生界深埋碳酸盐岩潜山天然气获得重大突破,钻井揭示古生界气层垂向上显示分段性特征,该区储层主要受岩溶作用的控制,认识研究区岩溶垂向分带特征是预测优质储层和油气分布的关键。文章利用岩心、薄片、电性特征、能谱测井U值、C、O、Sr同位素等资料,结合水动力作用的大小、方向,综合分析认为,岩溶储层垂向具有分带性特征,自上而下分为表层风化带、垂直渗流带、水平潜流带和深部缓流带,且其岩电特征与溶蚀作用强差异性控制了储层发育段。研究表明优质储层主要分布于表层风化带、水平潜流带,且分别在不整合面以下20 m范围内和距不整合面50~200 m,此外在溶蚀作用弱的深部缓流带,白云岩发育区则是潜在优质储层发育带。明确岩溶垂向分带特征及储层发育规律,对下一步碳酸盐岩区油气勘探具有一定的指导意义。

A great breakthrough of gas exploration has been gained in deep Paleozoic carbonate reservoirs of Buried Hill in the southwestern Bozhong Sag,Bohai Bay Basin.Drilling wells reveal that the vertical zonation of the Paleozoic gas layers was mainly controlled by karstification in this region.Recognizing the characteristics of vertical karst zoning in the study area is the key to predict the distribution of high-quality reservoirs.According to cores,thin sections,logging characteristics,spectrum logging U values,C-O-Sr isotope compositions,combined with the hydrodynamic magnitude and direction,karst reservoirs can be vertically divided into four zones from top to bottom:surface weathering zone,vertical percolating zone,horizontal underflow zone,and deep slow flowing zone.The differences of lithologic-logging properties and denudation intensity were closely related to the development of high-quality reservoirs.It is showed that the high-quality reservoirs are mainly distributed in the surface weathering zone(20 m under unconformity)and horizontal underflow zone(50 to 200 m beneath unconformity).In addition,the potentially high-quality reservoirs are developed in dolomiteexisting area of deep slow flowing zone with weak denudation.Therefore,clarifying the characteristics of karst vertical zoning and the patterns of reservoir development have important guidance for exploration of oil and gas in the future.