四川盆地奥陶系岩相古地理与勘探潜力

Lithofacies Paleogeography and Exploration Potential of Ordovician in Sichuan Basin

在前人研究基础上,依托露头和钻井资料,以沉积相分析为核心,结合四川盆地构造演化,采用单因素分析多因素综合法,以"组"为单元编制了奥陶纪岩相古地理图。奥陶纪四川盆地及邻区总体呈现西高东低的古地理格局,自西向东发育滨岸相、混积潮坪相、局限台地相、开阔台地相和斜坡相—盆地相。从岩相古地理视角对成藏条件的分析表明:奥陶系五峰组沉积期四川盆地主体属于局限海环境,发育了一套优质烃源岩,此外,与奥陶系临近的上覆志留系龙马溪组和下伏寒武系筇竹寺组烃源岩在有断层沟通的情况下可提供有效气源;奥陶系碳酸盐岩总体致密,白云石化、表生溶蚀和裂缝的存在是储层形成的关键因素,对应发育了桐梓组—红花园组颗粒滩白云岩储层、岩溶储层和宝塔组裂缝储层等三类储层;奥陶系发育下部(下生上储)和上部(上生下储)两套成藏组合,具有较好的勘探潜力。

Based on the outcrop and drilling data,we reconstructed the Ordovician lithofacies paleogeography map in Sichuan Basin with a method of single-factor analysis and multi-factor comprehensive mapping.There developed coastal facies,alluvial tidal flat facies,limited platform facies,open platform facies and slope-basin facies from west to east.According to the hydrocarbon source conditions,Late Ordovician Wufeng Formation developed in limited sea is high-quality source rocks,in addition,when connected by faults,the overlying Silurian Longmaxi Formation and the underlying Lower Cambrian Qiongzhusi Formation are effective source rocks.According to the reservoir conditions,dolomitization,supergene dissolution,and fracture development are the key factors for the formation of Ordovician carbonate reservoirs.Correspondingly,three types of reservoirs developed including particle-gravel dolomite reservoir,karst reservoir in Tongzi Formation and Honghuayuan Formation,and crack reservoir in Baota Formation.The Ordovician developed two sets of reservoir assemblages,i.e.,the lower part and the upper part,which have good exploration potential.