吐哈盆地台北凹陷深盆气成藏地质条件

深盆气藏是指在特殊地质条件下形成的、具有特殊圈闭机理和分布规律的非常规天然气藏。台北凹陷继承性发育的构造背景具备了形成深盆气藏的构造条件,目前仍在生气的中-下侏罗统煤系源岩在第一生气高峰阶段生成的天然气构成了本区深盆气藏的主要气源。中、下侏罗统储集层物性以低孔低渗为主,西山窑组及其以下储集层的孔隙度通常小于10%,渗透率小于4x10^-3μum²。三套区域性盖层与局部盖层相匹配,在空间上构成了严密的顶封和底封条件。台北凹陷深盆气的最有利勘探区位于小草湖洼陷,源-藏伴生、气层负压异常、中-下侏罗统致密砂岩普遍含气、无统--气水界面、气水关系倒置等现象均表明该区发育深盆气藏。预测小草湖洼陷深盆气地质储量为5658×10⁸m³,勘探前景良好。

The Geological Conditions for Forming Deep-Basin Gas Accumulation in Taibei Sag, Turpan-Hami Basin

As a kind of abnormal gas accumulation, deep-basin gas is trapped with particular geological conditions and has particular trapping mechanism and distribution pattern. The tectonic framework with the characteristics of continuous deposition provides favorable structural condition for deep-basin gas accumulation in Taibei sag. The natural gas generated during the first stage for the Middle- Lower Jurassic coal-measure source rock which still generating gas currently is the main source for deep-basin gas accumulation. The sandstone of Middle- Lower Jurassic is low-porosity and low-permeability. The porosity and permeability of Xishanyao formation and the deeper reservoirs are usually less than 10% and 4×10^-3μm²,respectively. The assemblage of 3 sets of regional cap rocks and some local cap rocks forms tight top-covering and bottom-covering. The most favorable region for deep-basin gas exploration in Taibei sag is located in Xiaocaohu sub-depression. The characteristics of source-accumulation being a unity, abnormally low pressure, gas bearing in large area, uncontrolled by a tectonic isobath, gas-water inversion indicate the existence of deep-basin gas accumulation.