Study On The Development Law Of Dominant Seepage Channels In Y Formation Layered Sandstone Reservoir Of P Oilfield In South Sudan

The dominant seepage channel controls the remaining oil distribution in the high water cut period of layered sandstone reservoir,revealing the distribution law of dominant seepage channel is of great significance to realize stable oil and water control and improve oil recovery.In this paper,Y group of typical bedded sandstone reservoir in P oilfield of Central South Sudan in M basin of inland rift basin in Africa is taken as an example.Based on the data of core,well logging,scanning electron microscope,water injection profile and production performance,the geological static and production identification characteristics of the development of dominant seepage channels are analyzed firstly.The distribution position of dominant seepage channels in Y group dominated by braided river and meandering river deposits is semi-quantitatively identified by the identification method combining static data and dynamic data.Then the main influencing factors of dominant seepage channels in the study area are summarized,and the distribution law of dominant seepage channels is clarified by analyzing the distribution relationship between dominant seepage channels and sedimentary microfacies,sand body connectivity and physical properties.Finally,according to the location of interlayer,water type,rhythm type and other variable factors,considering the relationship between dominant seepage channel and residual oil distribution,the distribution model of dominant seepage channel suitable for layered sandstone reservoir is established.After the formation of the dominant seepage channel,there will be geological and production characteristics such as the decrease of mud content,the increase of permeability,the decrease of resistivity,the increase of water content and the improvement of water absorption capacity.A total of 30 dominant seepage channels were identified in the study area.The dominant seepage channel is parallel to or intersected at a small angle with the source and the direction along the river in the plane;vertically,it is developed in high-porosity and high-permeability sandstone layers with high penetration coefficient,high variation coefficient and large gradation in the sand group where the perforation layer is located.The dominant seepage channel in the layer preferentially develops at the bottom of the positive rhythm sand body,but the tight mudstone interlayer will affect its development strength and longitudinal distribution.The factors affecting the dominant seepage channel are divided into reservoir geological factors and reservoir engineering factors.The reservoir geological factors include plane heterogeneity,interlayer heterogeneity,intra-layer heterogeneity and micro heterogeneity.The reservoir engineering factors include injection-production well spacing,injection-production intensity and fluid properties.The distribution mode of dominant seepage channel in layered sandstone reservoir can be divided into three levels: water control mode between sand groups,interlayer control mode within sand groups and rhythmic control mode within layers.The water control mode between sand groups can be subdivided into artificial water injection control mode and edge and bottom water control mode.Residual oil is mainly distributed in the sand group with low injection water sweep coefficient and no dominant seepage channel,or in the sand group with dominant seepage channel-upper sandstone layer and upper positive rhythm sand body.Improving water flooding residual oil recovery can be controlled by fine layered water injection and dominant seepage channel.