天草凹陷下白垩统层序地层分析及有利区带预测

LOWER CRETACEOUS SEQUENCE STRATIGRAPHY ANALYSIS AND PROMISING AREA PREDICTION IN TIANCAO SAG

应用天1井岩性、电性、古盐度、古气候和地层倾角等资料,建立了银额盆地天草凹陷层序地层学等时地层格架,将天草凹陷下白垩统划分为4个三级层序。在此基础上,以层序或体系域为单元,充分利用二维地震资料,系统分析了层序Ⅰ和层序Ⅱ的地震相平面展布特征。天草凹陷下白垩统K_1b^2、K_1s^2时期发生了两次大规模湖侵,发育两套主力烃源岩,在时空配置上形成K_1b^1-K_1b^2、K_1b^2、K_1b^2-K_1s_1三套生储盖组合。根据沉积相、沉积演化研究成果,结合构造特征分析,预测了下白垩统西部陡坡带和东部缓坡带两个有利区带,展示了天草凹陷下白垩统具备中小型油气田的勘探前景。

By use of lithology, electricity, palaeosalinity, palaeoclimate and stratigraphic dip data of Well Tianl, a sequence stratigraphic isochronic formation framework of Tiancao sag in Yine basin has been established, in which the lower Cretaceous is divided into 4 third order sequences. On this basis, taken a sequence or system tract as an unit, the areal distribution features of seismic facies of sequence Ⅰ and Ⅱ are analyzed systematically, by fully use of 2D seismic data. In lower Cretaceous K_1b^2 and K_1s^2 stage, Tiancao sag has experienced two massive lake transgressions, thus two sets of main source rock developed, and three sets of source-reservoir-caprock assemblage were formed on the chronic and spatial configuration. Based on the research results of sedimentary facies and sedimentary evolution, and structure feature analysis, the west lower Cretaceous steep slope and east ramp areas are predicted as promising targets, which shows the wide prospect of this sag in oil and gas exploration.