陕甘宁盆地陇东地区长3油组坳陷湖盆岩性油藏成藏模式

Accumulation modes of lithologic oil pools in Chang-3 oil formation in Longdong area, Shan-Gan-ning Basin

陇东地区三叠系延长组位于陕甘宁盆地陕北斜坡的南部 ,其中长 3油组发育了一套坳陷型湖泊三角洲前缘碎屑岩沉积 .该区构造发育简单 ,缺乏断层 ,油藏类型属岩性油藏 .通过对长 3油组岩性油藏的储油砂体成因和成藏要素进行分析 ,认为该区长 3油组油藏特征主要反映在储油层成因和圈闭两种因素上 ;储油砂体下伏深水泥岩、巨厚的坝上河砂体、“无根”的断头砂和单斜背景上的小背斜等是油藏 4种主要组合要素 .油气藏的形成有 4种模式 :古地形巨厚砂岩差异压实小幅背斜成藏模式 ;单斜构造背景上的上倾尖灭油藏成藏模式 ;烃源岩内砂岩透镜体圈闭成藏模式 ;鼻状构造高部位与砂体匹配构成构造—岩性圈闭成藏模式 .

Upper Triassic Yanchang Formation in Longdong area is in the south of northern Shaanxi slope of Shaan-Gan-Ning Basin, and a set of downwarped lake delta front clastic sedimentation developed in Chang-3 formation. Based on the analyses of geneses of reservoir sandstone and accumulation elements of lithologic oil pools for Chang-3 oil formation, it is held that the reservoir characteristics of Chang-3 formation are mainly controlled by oil reservoir geneses and traps; there are main four composite elements of lithologic oil pools, they are oil-bearing sandbody underlying deepwater mudstone, huge thick river-over-bar sandbody, non-root broken-end sandbody and low-angle anticline on the background of monoclinal structure; there are also four oil accumulation modes, they are low-angle anticline petroleum accumulation formed by the differential compaction of palaeogeomorphic huge thick sandstone, updip pinchout petroleum accumulation on the background of monoclinal structure, sandstone lens trapping petroleum accumulation in hydrocarbon source rock and structure-lithological trap petroleum accumulation formed through matching of the high place of nose structure with sandbody.