鄂尔多斯盆地上古生界气藏特征

CHARACTERISTICS OF UPPER PALEOZOIC GAS RESERVOIRS IN E′ERDUOSI BASIN

鄂尔多斯盆地是一个构造简单的大型多旋回克拉通盆地 ,面积约 2 5× 10 4 km2 。上古生界石炭—二叠系下部沉积的暗色泥岩、煤层和石灰岩有机质含量高、热演化程度高、生气能力强 ,为古生界气藏的形成提供了充足的气源 ;其中下部为一套河流、三角洲砂岩沉积 ,是上古生界的主要储层 ;而其上部的河漫湖相泥质岩为良好盖层。盆地周边在燕山期构造活跃 ,砂体发育 ,以构造圈闭为主 ;盆地内部构造稳定 ,在倾角不到 1°的西倾单斜上 ,南北展布的河流三角洲复合砂体与侧向河流间湾泥质岩 ,形成了近南北向的大型岩性圈闭。因此 ,盆地周边发育以构造控制为主的小型气藏 ,盆地内部则以大型岩性气藏为主 ,盆地西缘断褶带胜利井气藏和伊陕斜坡上的陕 141井区下二叠统山西组山 2段气藏等的存在就反映了这一特征。

E′erduosi Basin is a tectonically simple,large-scale,multicycle,cratonic basin with an area of 25×10 4km 2。The melanic mudstones,coal beds and limestones in the lower part of the Carboniferous-Permian of the Upper Paleozoic are of high organic matter content,high thermal evolution level and high gas generating potential,which provided sufficient gas source for forming Paleozoic gas reservoirs;their middle-lower part is a set of sandstones of fluvial facies and delta facies,which are the major reservoirs in the Upper Paleozoic and the argillaceous rocks of alluvial flat facies in their upper part are the good cap-rocks.The structural traps are mainly found around the basin′s circumference with developed sandbodies,where activated tectonically during Yanshan epoch;the interior of the basin was stable tectonically and a south-north large-sized lithological trap was formed in the south-north fluvial-delta complex sandbodies sealed laterally by the argillaceous rocks of fluvial faciec on the west-tilted monocline with dip angles of less than 1°.Therefore,small-sized structural gas reservoirs are mainly formed around the basin′s circumference and large-sized lithologic gas reservoirs in the interior of the basin,which have been proved by the Shenglijing gas reservoir in the fault-flod zone along the west edge of the basin and by the Shan-2 member gas reservoir of the Shanxi Formation,the Lower Permian,at the area of well Shaan-141 on the Yishaan slope.