沧东凹陷孔二段控藏机制研究与勘探成效

Reservoir-controlling Theory and Exploration Results of Member 2 of Kongdian Fomation,Cangdong Sag

沧东凹陷为渤海湾盆地中部、以古近系孔店组沉积为特色的坳断转换型湖盆。古近纪早期坳陷与晚期断陷叠置,形成北段反转型、南段继承型两大构造区。孔二段为早期坳陷湖扩期沉积,受盆外物源及古坡折控制,古湖盆边缘发育辫状河三角洲沉积,湖盆中心发育远岸水下扇,岩性主要为白云岩、过渡岩类及高丰度泥页岩类。作为沧东凹陷的主力优质烃源岩层系,在有效生油岩范围内,盆缘砂岩常规油藏与湖盆主体致密油叠置连片、满凹含油,形成"连续性"油气分布。受南北构造差异发育控制,南段继承性斜坡顺向供砂、古侵蚀沟槽控砂、斜坡高部位富砂,中低部位源储共生,油气富集;北段反转型斜坡低部位富砂,中高部位源储一体,利于成藏,二者油气成藏模式有别。通过分层系立体评价,完成预探部署方案,部署预探井17口,经钻探实施,实现了斜坡区岩性油藏与湖盆主体区致密油预探突破,形成5000万吨级规模增储区。

Cangdong sag is located in the center of Bohaiwan basin, is a depression-fault transited lacustrine basin characterized by the Paleogene sediments. Due to the overlap of tectonic activities during the early Paleocene depres- sion and the late Paleocene fault, two main tectonic plays formed in this sag： the north anti transformation tectonic play and the south inherited tectonic play. The member 2 of Kongdian formation deposited in the early stage of sag expansion. Its developed sedimentary facies were affected by external basin source provenance and paleo slope break., braided river delta in the margin and far shore submarine fan in the basin center, where rock types are mainly dolomite, transitional rocks and high abundance ratios of shale. Conventional sandstone reservoirs in basin margin and tight reservoirs in the basin center overlapped horizontally and vertically in basin scale, forming the continuous oil distribution within the scope of effective source rocks. Due to the differences of controlling tectonic activities in the north and the south plays, different depositional systems and different hydrocarbon enrichment models formed in these two plays. In the south tectonic play, sand-rich sediments display on the high part of slope. In the middle and low part of the slope, both sand-rich and mud-rich sediments deposited. This co-existence of reservoir and source rock favors hydrocarbon enrichment. While in the north play, the low part of slope is sand-rich and the middle and high part of slope are both sand-rich and mud-rich. Thus, hydrocarbon in the north tectonic play may favor in rich in the middle and high part of slope. Based on the analysis of each strata in three dimensions, pre-exploration proposals have been made and 17 wildcat wells have been drilled. A big breakthrough has been made in the exploration of the lithologic reservoirs in the slope and tight reservoirs in central basin, forming a new exploration area with fifty mil- lion tons reserve.