四川盆地深层—超深层碳酸盐岩油气成藏条件与勘探潜力

Hydrocarbon accumulation conditions and exploration potential of deep–ultradeep carbonate rocks in Sichuan Basin

四川盆地深层—超深层碳酸盐岩层系分布面积约为10×10^(4)km^(2),源—储叠合有序分布,勘探潜力巨大。通过系统梳理四川盆地深层—超深层基本石油地质条件,分析存在的勘探类型和其勘探潜力,指出未来勘探方向。研究认为:(1)“裂陷—坳陷”构造旋回控制深层—超深层碳酸盐岩储层分布,区域上发育4套厚层白云岩储层,其分布主要受控于沉积相带,最有利储层发育区位于裂陷边缘台缘带;(2)多期隆—坳相间的构造格局控制了四川盆地海相烃源岩广覆式发育,其中最优质的烃源岩包括寒武系麦地坪组—筇竹寺组、志留系龙马溪组和二叠系龙潭组;(3)常规孔隙型碳酸盐岩储层主要分布于川西北和川中—川东地区,层系以震旦系—寒武系和二叠系为主,埋藏深度在6000~10000m,形成下生上储、旁生侧储和上生下储三种成藏组合,成藏条件优越,扬子克拉通西北缘灯影组台缘带和长兴组礁滩、川东震旦系与二叠系礁滩体是未来规模增储重点区带,资源规模超万亿立方米;(4)泥灰岩非常规储层层系以茅口组一段(茅一段)和雷口坡组三段二亚段(雷三段二亚段)为主,源储一体成藏,埋深在3000~6000m,资源潜力超3×10^(12)m^(3),有望成为重大接替领域;其中茅一段有利区主要分布在川东—蜀南地区,雷三段二亚段有利区主要分布在川中地区。

The deep-ultra-deep carbonate rock series in Sichuan Basin have an area of about 10×10^(4)km^(2),with superposition and orderly distribution of source rock and reservoir,showing huge exploration potential.After systematically studying the basic petroleum geological conditions of deep-ultra-deep formation in Sichuan Basin,the possible exploration types and their exploration potential are analyzed,and the future exploration orientation is put forward.The study results show that:(1)The“rift-depression”structural cycle controlled the distribution of deep-ultra-deep carbonate reservoirs.Four sets of thick dolomite reservoirs were developed in the region,and their distribution was mainly controlled by sedimentary facies zones,with the most favorable reservoir developed in platform margin at the edge of the rift.(2)The structural pattern of multi-stage alternating uplift and depression controlled the widespread marine source rocks in Sichuan Basin,among which source rocks with the best quality included the Cambrian Maidiping Formation-Qiongzhusi Formation,Silurian Longmaxi Formation,and Permian Longtan Formation.(3)The conventional porosity type carbonate reservoirs were mainly developed in the Sinian-Cambrian and Permian in the northwestern and central-eastern Sichuan Basin,with burial depth of 6000-10000 m.Three types of hydrocarbon accumulation combinations were formed,i.e.,lower source rock and upper reservoir,side source rock and side reservoir,and upper source rock and lower reservoir,with superior hydrocarbon accumulation conditions.The key zones for increasing reserves on a large scale include Dengying Formation platform margin and Changxing Formation reef flat in the northwestern margin of Yangtze Craton,and the reef flat in the lower combination in the Sinian and Permian in the eastern Sichuan Basin,with a resource scale of more than one trillion tons.(4)The unconventional marl reservoirs were mainly developed in the first member of Maokou Formation(Mao 1 member)and the second sub-member of the third member of Leikoupo Formation(Lei 3^(2) sub-member),with integrated source rock and reservoir,burial depth of 3000-6000 m,and resources of more than 3×10^(12)m^(3),which is expected to be a major replacement field.The favorable area of Mao 1 member is mainly distributed in the eastern-southern Sichuan Basin,while that of Lei 3^(2) sub-member was mainly distributed in the central Sichuan Basin.