咸化湖盆缓坡带碳酸盐岩岩石学特征及沉积模式——以东营凹陷古近系沙四上亚段为例

Petrological Characteristics and Sedimentary Mode of Salinized Lacustrine Carbonate:A Case Study on Upper Part of the Fourth Member of Shahejie Formation in Dongying Sag

咸化湖盆中广泛发育的碳酸盐岩厚度薄、相变快,储层预测难度大。综合利用岩心、薄片、测井及地震等资料,对东营凹陷南部缓坡带沙四上亚段的湖相碳酸盐岩进行系统研究,结果表明:碳酸盐岩的主要岩石类型为内碎屑颗粒云岩、鲕粒云岩、生物碎屑(灰)云岩、泥晶灰(云)岩。由岸向湖方向,高能的亮晶生物云岩和砂屑灰云岩逐渐向低能的泥晶灰(云)岩转变,单层厚度逐渐减薄。沿岸带地形平坦,碳酸盐岩浅滩平面呈带状分布,单层厚度大,储层中陆源碎屑含量高,残余原生和大气淡水溶蚀孔隙较为发育。近岸带内地形起伏较大,高能浅滩分布于局部的高部位,碳酸盐岩成分较纯,但强烈的胶结作用造成原生孔隙发育差。远岸带内主要发育深灰色泥岩及油页岩夹薄层的泥-微晶白云岩,泥晶白云岩主要分布于局限洼地内,储集空间以裂缝和晶间孔隙为主。沿岸带内广泛发育的高能颗粒碳酸盐岩浅滩是勘探的主要方向。

The widely developed carbonate rocks in the salty lake basin are thin in thickness and have fast facies change,which makes it difficult to predict the reservoir.The lacustrine carbonate rocks in the upper part of Es4 member of the southern gentle slope in Dongying sag are systematically studied based on core,thin section,well logging and seismic data.The results show that the lithofacies of lacustrine carbonate in gentle slope zone includes dolomitized intraclast grainstone,bioclast grainstone,oolitic grainstone,lime mudstone and siliciclastic-bearing mudstone.According to the difference of palaeogeomorphology and palaeohydrogeology,the whole gentle slope zone can be divided into littoral zone,sublittoral zone and profundal zone,the content and thickness of high-energy grainstones decrease whereas lime mudstones increase from the shoreline to the basin centre.The coastal zone is flat,the carbonate shoals are distributed in strips,the thickness of single layer is large,the content of terrigenous clasts in the reservoir is high,and the residual primary pores and atmospheric fresh water dissolution pores are relatively developed.The topography in the nearshore zone fluctuates greatly.High energy shoals are distributed in local high parts.The carbonate rock is pure,but the strong cementation causes poor development of primary pores.In the far shore zone,dark gray mudstone and oil shale mixed with thin layer of mud microcrystalline dolomite are mainly developed.Micritic dolomite is mainly distributed in limited depressions,and the reservoir space is mainly composed of fractures and intergranular pores.High energy granular carbonate shoals widely developed in the coastal zone are the main exploration target.