冀中坳陷斜坡类型及油气成藏认识

Types and hydrocarbon accumulation of slope zones in Jizhong Depression

为探索冀中坳陷斜坡区油气勘探接替领域,从凹陷结构出发,结合成因和地貌特征,将斜坡划分为沉积斜坡、构造斜坡和构造—沉积复合斜坡三种类型;根据地貌特征,斜坡又可进一步划分为陡窄型、平台型和宽缓型。通过油气勘探实践,认为:①以蠡县斜坡为代表的平台型沉积斜坡具备自身生油、油气长距离运移条件,源外成藏潜力大;弱构造变形区发育具基底背景的构造脊,它与薄砂体配置可形成“构造脊+薄储层”岩性圈闭。②以束鹿西斜坡为代表的陡窄型沉积斜坡直接与生油洼槽相接,从斜坡到凸起均可成藏;粗相带的砾岩体可被上倾方向的平原相泥岩遮挡,形成岩性油藏;规模小的潜山被古近系砾岩遮挡,可形成潜山圈闭,陡窄型斜坡也可获规模油气储量发现。该成果可为地质条件相似的断陷盆地斜坡油气勘探提供参考。

According to the depression structure,slope genesis,and geomorphic characteristics,this paper divides the slope zone into three types of sedimentary slope,structural slope,and structural-sedimentary slope to study the exploration potential of the slope zone in Jizhong Depression.The sedimentary slope can be divided into the steep narrow type,platform type,and wide gentle type.Results from oil and gas exploration practices are as follows:①The platform-type sedimentary slopes represented by the Lixian slope have conditions for oil generation and long-distance migration of oil and gas,with great potential for accumulation outside the source.The structural ridge with a basement background is developed in the weak structural deformation area and can form a lithologic trap of“structural ridge+thin reservoir”by matching with thin sand body.②The steep narrow sedimentary slopes represented by the Shuluxi slope are directly connected with the oil-generating subsag,and reservoirs can be formed from slopes to uplifts.The conglomerate in the coarse sedimentary facies belt can be shielded by the plain facies mudstone in the updip direction,forming lithologic reservoirs.The buried hill with a small structural scale is blocked by the Paleogene conglomerate,which can form a buried hill trap.Additionally,large reserves can also be found on steep narrow slopes.This study can provide references for oil and gas exploration in slope zones of fault basins with similar geological conditions.