鄂尔多斯盆地奥陶系储层展布及勘探潜力

Distribution and exploration potential of Ordovician reservoir in Ordos basin

鄂尔多斯盆地奥陶系沉积时期,处于“三隆两鞍两坳陷”的古构造格局。3个隆起在平面上呈“L”型展布,共同控制着奥陶系的沉积相带,并控制着不同类型储层的区域展布。奥陶系主要的储集类型包括东部坳陷的盐下储集体、古隆起斜坡带的风化壳岩溶储集体、古隆起鞍部的马家沟组四段白云岩储集体、古隆起西部的中奥陶统重力流储集体和古隆起南部斜坡带的生物礁储集体。风化壳岩溶是最有利的储集体,在该储集体中目前已发现靖边大气田。其他4种类型储集体的勘探虽然还未取得实质性进展,但结合储层特征及油气运聚分析,仍存在较大的勘探潜力,是开拓鄂尔多斯盆地下古生界油气勘探新领域的关键所在。

The Ordovician in Ordos basin had been deposited in a ＂three uplifts-two saddles-two depressions＂ paleotectonic framework. The three uplifts were horizontally distributed as the letter ＂L＂ and together controlled the sedimentary facies of Ordovician and the regional distributions of different types of reservoirs. The main reservoir types in Ordovician include sub-salt reservoirs in the eastern depression, residuum karst reservoir on the slope zone of the palaeohigh, dolomite reservoirs in the 4th member of Majiagou Formation on the saddle of the palaeohigh, Middle Ordovician gravity flow reservoirs in the western part of the palaeohigh, and bioherm or reef reservoirs on the southern slope zone of the palaeohigh. Among these reservoir types, the residuum karst reser- voirs are the most favorable, and the large Jingbian gas field has been discovered in this reservoir type. Based on analysis of reservoir characteristics and hydrocarbon migration and accumulation, it is believed that the other 4 types of reservoirs still have relatively large exploration potentials, though no substantial progress has been made in exploration, thus they would be the key frontiers for exploration in the Lower Paleozoic in Ordos basin.