细粒相沉积地质特征与致密油勘探——以渤海湾盆地沧东凹陷孔店组二段为例

Geologic features of fine-grained facies sedimentation and tight oil exploration: A case from the second Member of Paleogene Kongdian Formation of Cangdong sag, Bohai Bay Basin

以渤海湾盆地沧东凹陷古近系孔店组二段湖盆中部细粒相区600多米连续整体取心、上万块次系统分析联测及配套测录井资料为基础,运用传统石油地质学、沉积岩石学及致密油气形成新理论新方法,对孔二段细粒相区沉积特征进行了研究。结果表明,沧东凹陷孔二段是孔店组最大湖泛期的沉积,半深湖—深湖亚相细粒沉积分布较广,主要发育细粒长英沉积岩类、细粒混合沉积岩类及白云岩类,而黏土岩类不发育,细粒岩类具有"岩石成分多,优势矿物少;碎屑矿物多,黏土矿物少;方沸石多,黄铁矿少;脆性矿物多,石英含量少;岩石类型多,油页岩少;致密储集层多,无裂缝的少;优质烃源岩多,非烃源岩少;高频旋回多,单一沉积少"等特点。这些认识更新了以往关于陆相闭塞湖盆中部仅以"泥页岩"烃源岩沉积为主的观点。在地质认识指导及配套工程工艺技术的支撑下多口探井获工业油流,展示了陆相湖盆细粒相区致密油勘探的良好前景。

Based on analysis of successive and whole cores over six hundred meters from the second Member of Kongdian Formation （Kong 2 Member） of fine-grained facies zone in central lake basin of Cangdong sag, ten thousands of systematic and joint analysis data, and the matching logging data, the sedimentary characteristics in the fine-grained facies zone is examined by means of traditional petroleum geology, sedimentology, and new theory and method of tight oil and gas generation. The Kong 2 Member is the sedimentation during the maximum lake flooding in the Kongdian Formation. Fine-grained sedimentation of half-deep lake to deep lake are widely distributed, the fine-grained feldspar-quartz contained sedimentary rock, fine-grained mixed sedimentary rock, and dolomite are developed, and the clay rock is poorly developed. The fine-grained rocks have these features as follows： more rock compositions, less advantageous minerals; more debris minerals, less clay minerals; more analcites, less pyrites; more brittle minerals, less quartz; more rock types, less oil shale; more tight reservoirs with less non-cracked reservoirs; more high-quality source rocks, less non-source rocks; more high-frequency cycle sediments, less single sediments. These understandings updated the former view that only mud shale source rock was dominantly developed in the closed continental lake. With the help of geologic research and matched engineering technologies, several exploration wells have produced industrial oil flows, showing a good prospect of tight oil exploration in fine-grained facies zones of continental lacustrine basins.