安塞油田南部侏罗系古地貌与延安组油气成藏关系

Paleomorphology of Jurassic in the southern area of Ansai Oilfield and its relationship with oil and gas accumulation in Yan’an Formation

为了解古地貌与油气成藏的关系,以安塞油田南部地区为例,利用该地区丰富的钻井与测井资料,采用印模法恢复了该地区侏罗纪古地貌形态,并在此基础上详细分析了古地貌对延安组成藏的控制作用。安塞南部侏罗系主要发育河谷、陡坡和支沟3种古地貌单元:河谷主要发育于研究区西南地区,河谷走向近东西向,是由强烈的河谷下切作用形成的;陡坡为高地与古河谷之间的过渡地带,宽度为3.0~9.5 km,可进一步将其划分为陡坡区与缓坡区;支沟对延长组地层的冲蚀及对陡坡的支解起重要作用,使地层边缘发生破碎并形成坡咀。河道砂体及支沟是油气运移的良好通道,陡坡区砂体为油气的有利储集体,而陡坡区内的有效构造圈闭或岩性上倾尖灭圈闭是安塞油田南部油气富集的潜力区。

In order to clarify the relationship between palaeoglandomorphology and hydrocarbon accumulation,the Jurassic palaeogeomorphology in the south area of Ansai Oilfield was reconstructed by impression method based on a large number of drilling and logging data.The controlling effect of palaeogeomorphology on the formation of Yan’an reservoir was analyzed.The result shows that there are three palaeogeomorphological units in Jurassic System in southern Ansai district:valley,slope and ditch.The river valley is mainly developed in the southwest of the study area,and the river valley is close to the east-west direction,formed by the strong undercutting of the valley.The slope is the transition zone between highland and ancient river valley.The slope width is 3.0-9.5 km,which can be further divided into steep slope area and gentle slope area.Ditches play an important role in the erosion of the strata of the Yanchang Formation and the decomposition of slopes,which can break up the edges of the strata and form slopes.Channel sand bodies and branch channels are good channels for oil and gas migration,sand bodies in slope area are favorable reservoirs for oil and gas.Micro-structures and lithologic traps influenced by palaeogeomorphology are favorable accumulation areas for oil and gas.