吐哈盆地沙尔湖洼陷煤层气成藏地质特征

Geologic Characteristics of Coal Seam Gas Accumulation in Shaerhu Sub-Sag, Tuha Basin

沙尔湖洼陷是吐哈盆地南缘一孤立的含煤洼陷,单煤层厚度达150m,煤阶为褐煤,是我国罕见的富煤洼陷。以现有地震、地质、钻井及各类分析测试资料为基础,详细论述了洼陷煤层气的成藏基本地质特点,明确了洼陷中侏罗统西山窑组(J2x)巨厚煤层的宏观、微观组成、孔隙发育特征及煤层气的吸附性。洼陷内西山窑组巨厚煤层具有形成生物成因煤层气藏的地质条件,洼陷斜坡下倾部位易形成较高饱和度的煤层气藏,是勘探的有利场所。

Shaerhu sub-sag is an isolated coal-bearing sub-sag in southern margin of Tuha basin and a peculiar coal-enriched sub-sag in China, with the thickness of single coal seam of 150 m. The coal step belongs to lignite. Based on the existing seismic, geologic, drilling and various analytical testing data, the basic geologic features of its accumulation into gas reservoir are fully discussed. The macro and micro composition, pore growth properties and adsorption of coal seam gas of Xisnanyao formation （J2x） in this sub-sag are identified. It is concluded that this coal seam in huge thickness possesses the geologic conditions for forming coal seam gas reservoir originated from biologic origin; the coal seam gas reservoir with high saturation is easily formed in the lower position of the sub-sag＇s slope, being a favorable area for exploration.