台北西部隐蔽油气藏形成条件及勘探目标

FORMING CONDITIONS OF SUBTLE RESERVOIRS AND EXPLORATION PROSPECTIVE AREA IN WEST TAIBEI SAG

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三个二级层序、十个三级层序,SQ9(J_2q)、SQ8(J_2s^2)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,岩性圈闭成生模式主要有四种: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。其中前三者为隐蔽圈闭的主要成生类型,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,并已取得勘探重要进展。

In the initial stage of subtle reservoir exploration in medium to shallow formations of Taibei sag Tuba basin, so far, three kinds of subtle reservoirs (stratigraphic, structural and composite structural-lithologic reservoirs) have been found. Since both the amount and reserves of discovered subtle reservoirs are low, there still is great potential of exploration for them. The medium to shallow formation in Taibei sag were divided into three second-order sequences and ten third-order sequences, among which rising cyclothems of SQ (J_2q) and SQ8 (J_2s^2) base datum are major exploration targets for subtle reservoir (lithologic). Qiquanhu and Subashi braided river delta deposition systems developed there, where the sedimentary sand body is dominated by area slope and slope break belt. There are four main forming modes of lithologic traps: delta front onlap in slope belt, delta front toplap in slope break belt, tilt frontal sand body and sublacustrine fan_slope fan in slope break belt respectively, among them the first three modes are major forming style of subtle reservoirs. Major targets for subtle reservoir exploration in the near future include Putaogou member in north Huoyanshan slope, east slope of Pubei, nose-like palaeohigh of Huobei, Subashi and Lianmuqin region, around Shengbei secondary sag.