Study On Micro-pore Structure And Seepage Characteristics Of Es₂-Es₃ Reservoir Of Lixian Slope

The study of micro pore structure and seepage characteristics of low permeability reservoir is of great significance to improve water drive development effect and enhance oil recovery.The reservoir of Es₂-Es₃ member in Lixian slope of Huabei Oilfield is a typical low permeability sandstone reservoir.Due to the unclear understanding of the microscopic pore structure and seepage characteristics of the reservoir,with the deepening of exploration and development,many problems are gradually exposed,such as increased seepage resistance,small effective displacement radius,increasing pressure of water injection well and no injection,low fluid production of production Wells and fast water cut rise of effective Wells,which seriously restrict the effective development of the late oilfield.This article selects coring data of 12 coring wells in the study area,through the property test,the casting thin sections and scanning electron microscopy（sem）,granularity analysis,high-pressure mercury injection and constant velocity mercury injection,nuclear magnetic resonance（NMR）,relative permeability experiments and real sandstone visual displacement experiment and start-up pressure gradient testing means such as the combination of further reveals the microscopic pore structure characteristics,occurrence characteristics,movable fluid seepage characteristics,start-up pressure gradient variation characteristics and its influencing factors,the analysis from the microscopic view control factors influencing development effect of low permeability reservoirs.At the same time,based on the starting pressure gradient,the calculation formula of reasonable well spacing in low permeability reservoir is established.The throat radius of the reservoir in the study area is mainly concentrated in the range of0.3-3μm,with an average of 1.9μm.The developed pore-throat assemblage is dominated by large medium thin throat,large pore-throat radius,non-piston oil displacement in the channel,and low oil displacement efficiency,with an average of 38.96%.At the same time,the heterogeneity of pore-throat is the main controlling factor affecting the final displacement efficiency of low permeability reservoir,while the size of pore-throat,reservoir physical property,displacement pressure and injection multiple are all secondary factors.The weaker the heterogeneity of pore-throat is,the better the final displacement effect is.With the decrease of gas permeability,the starting pressure gradient shows a progressive increasing trend.When the permeability is less than 1×10^-3μm²,the starting pressure gradient shows a rapid increasing trend.When the permeability is greater than 20×10^-3μm²,the starting pressure gradient has little change.This phenomenon indicates that in the development process of low permeability reservoir,when the actual permeability decreases to a certain value,the start-up pressure gradient will have a great influence on the reservoir development.