塔里木盆地西南坳陷下白垩统沉积相与储集层差异演化特征

Sedimentary facies and reservoir evolution divergence of Early Cretaceous sandstones in Southwest Depression of Tarim Basin

下白垩统是塔里木盆地西南坳陷主要的勘探层系之一,油气资源丰富但勘探程度较低,新近部署的多口探井均遭遇失利。为指导油气勘探部署,利用露头、钻井、地震和实验分析等资料,对下白垩统残余分布、沉积体系类型及储集层差异演化特征进行了研究。结果表明:①下白垩统沿南天山和昆仑山山前存在喀什北缘、乌泊尔构造带、棋北构造带和柯东构造带4个集中分布区,从山前向盆地内部减薄尖灭,改变了以往呈连续带状分布的认识。②古地貌控制下发育辫状河三角洲和扇三角洲2种沉积体系;其中,辫状河三角洲以前缘亚相为主,厚层水道砂体叠置连片分布,而扇三角洲由平原和前缘亚相构成,具有厚层短轴粗粒特征。③受原始沉积组分和后期成岩改造影响,下白垩统发育次生孔隙型和原生孔隙型2类储层,储集物性表现为中低孔中低渗—特低孔特低渗差异分布,喀什北缘和柯东构造带有利储层相对发育。

The Lower Cretaceous is one of the main exploration strata in Southwest Depression of Tarim Basin.It is rich in oil and gas resources but has a low degree of exploration.A number of the newly deployed explorato⁃ry wells suffered losses.In order to guide the next step of exploration and deployment,using the data of out⁃crop,drilling,seismic and experimental analysis,the residual distribution,sedimentary system types and reser⁃voir evolution difference of the Lower Cretaceous were studied.The results show as follows.Firstly,unlike the previous understanding of continuous belt-shaped distribution,there are four concentrated distribution areas of the Lower Cretaceous along the front of southern Tianshan Mountains and western Kunlun Mountains,which are Kashi Northern Margin,Wupper Structural Belt,Qibei Structural Belt and Kedong Structural Belt.The Lower Cretaceous is thinned and extinct from the mountain front to the interior of the basin.Secondly,under the control of ancient geomorphology,two sedimentary system types of braided delta and fan delta were devel⁃oped.Among them,braided delta is dominated by delta front subfacies,and thick channel sand bodies are super⁃imposed and contiguously distributed,while fan delta is composed of delta plain and delta front subfacies with the characteristics of thick and short-axis distribution and coarse grains.Thirdly,affected by original sedimenta⁃ry components and late diagenetic transformation,the Lower Cretaceous developed two reservoir types of sec⁃ondary pore type and primary pore type,and the reservoir physical properties are shown as the differential distri⁃bution of medium-low porosity and medium-low permeability to extra-low porosity and extra-low permeability.The favorable reservoirs are relatively distributed in Kashi Northern Margin and Kedong Structural Belts.