鄂尔多斯盆地中寒武统张夏组沉积相特征及岩相古地理分析

Sedimentary facies and lithofacies palaeogeography of the Middle Cambrian Zhangxia Formation in the Ordos Basin

截至目前,鄂尔多斯盆地寒武系碳酸盐岩油气勘探尚未得到足够重视,其油气地质条件研究仍处于起步阶段。为此,利用野外露头、岩心、测井和录井资料,综合分析了该盆地中寒武世张夏期沉积相类型及特征,认为张夏组属于碳酸盐岩台地相沉积,可进一步划分出局限台地、开阔台地、台地边缘、斜坡及深水盆地等5个沉积相及若干亚相和微相;通过统计张夏组地层厚度、碳酸盐岩颗粒含量、石灰岩含量、白云岩含量及深水沉积物含量,采用"单因素分析综合作图法"编制了张夏期岩相古地理图。研究结果表明:该区高能颗粒滩非常发育,以鲕粒滩为主,平面上主要分布在鄂尔多斯盆地西缘、南缘台地边缘及盆地东北部,其中,南缘台地边缘及东缘局限台地内白云岩化的鲕粒滩为最有利的储集相带,是新的油气勘探有利区。

No enough attention has ever been paid to the exploration of the Cambrian carbonate reservoirs in the Ordos Basin for a long time and the study of their petroleum geological conditions is still in initial stage.In view of this,outcrop observation,core data and logging data were integrated to analyze the types of sedimentary facies and their characteristics during the Middle Cambrian Zhangxia period.The deposits of carbonate platform facies in the Zhangxia Formation were divided into 5 facies(limited platform,open platform,platform margin,slope,and deep water basin) and several subfacies and microfacies.A statistical analysis was performed of the thickness and contents of carbonate grains,limestone and dolomite and deep water deposits.The lithofacies paleogeographic map of Zhangxia period was drawn by use of the method of 'single factor analysis and composite mapping'.The research findings reveal that the high-energy beach facies are well developed in this study area and are dominated by oolitic beach facies.They mainly occur around the western-margin platforms and the southern-margin platforms and the northeastern part of the basin.The dolomitized reservoirs of oolitic beach facies around the southern-margin platform and within the eastern-margin platform are the most favorable facies belts of reservoirs,which will be future exploration targets.