台北凹陷西部隐蔽油气藏形成条件及勘探有利区带

吐哈盆地台北凹陷中浅层隐蔽油气藏勘探尚处于初期阶段,已发现地层型、岩性型和构造-岩性复合型3类隐蔽油气藏,但其数量和储量所占比重小,隐蔽油气藏勘探潜力较大。台北凹陷西部中浅层可识别划分为3个二级层序、10个三级层序,SQ9(J2q)、SQ8(J2S2)基准面上升旋回是隐蔽油气藏(岩性油气藏)勘探的主要目的层序,发育七泉湖辫状河三角洲和苏巴什辫状河三角洲沉积体系,其沉积砂体受区域斜坡和坡折带构造背景的控制。岩性圈闭生成模式主要有4种:①斜坡带三角洲前缘上超型,②坡折带三角洲前缘顶超型,③前缘砂体后期掀斜型,④坡折带湖底扇-斜坡扇型。其中,前3种为隐蔽圈闭的主要生成类型。胜北次凹周缘的火焰山北坡葡萄沟段、葡北东斜坡、火北鼻隆、苏巴什鼻隆和连木沁鼻隆区是近期勘探隐蔽油气藏的主攻区带。

Formation Conditions and Exploration-favoring Areas of Subtle Reservoirs in West Taibei Sag

At the initial stage of subtle reservoir exploration in the shallow to medium formations of the Taibei Sag, Tuha Basin, so far, three kinds of subtle reservoirs (stratigraphic, lithologic and structural-lithologic reservoirs) have been found. Since both the amount and reserve of the discovered subtle reservoirs are small, a great exploration potential remains in the Taibei Sag. The shallow to medium formations in the west of the Taibei Sag were divided into three second-order sequences and ten third-order sequences, of which the rising cyclothems of SQ(J2q) and SQ8 (J2s^2) datum level are major exploration targets for the subtle reservoirs (lithologic). The depositional systems of Qiquanhu and Subashi braided river delta were developed there, where the sedimentary sand body is dominated by the regional slopes and slope break belts. There are four main modes the formation of lithologic traps: deltaic front onlap on the slope belt, deltaic front toplap on the slope break belt, lately tilted frontal sand body and sublacustrine fan--slope fan on the slope break belt, of which the first three modes are the major styles of the formation of subtle reservoirs. Major targets for subtle reservoir exploration in the near future include Putaogou Member on the north slope of Huoyanshan, the east slope of Pubei, the nose-like palaeohigh regions of Huobei, Subashi and Lianmuqin, around the Shengbei secondary sag.