Logging Evaluation Methods In Low Permeability Sandstone Reservoir And Its Application

Low permeability sandstone reservoirs are widely distributed in most petroliferous basins in China,and are research hotspots and difficult y in petroleum exploration and development.Low permeability sand stone reservoirs are characterized with small space,poor seepage ability,strong heterogeneity,complicated pore structures,changeable lithology and electric characteristics,complicated oil-water relationships and difficult to be distinguished.It's of great significance for the exploration and development of oil and gas to evaluate low permeability sandstone reservoirs effectively with well logging data.The paper studies pore structure evaluation,quantitative evaluation of physical parameters and the fluid identification of low permeability sandstone reservoirs,taking Es₃x¹ in Zhuang62-66 Area of Wuhaozhuang Oilfield as main research area.Meanwhile,taking the low permeability-tight sandstone reservoir of Quan 4 member reservoir of Rang 11 area in Jilin Oilfield as example,the evaluation of fracture and micro-fracture has also been carried out.The purpose is to provide theoretic foundations for logging evaluation of low permeability sandstone reservoirs.The main achievements are obtained as follows:?1?By intergrating data of geology,logging,development and analysis test,systematic analysis of log response mechanism of low-permeability reservoirs has been carried out from aspects of formation water salinity,lithology and mud invasion.Based on rock physical experiments,logging environment and geological background of low permeability sandstone reservoirs,we deepen the cognition to genetic mechanism of low-permeability reservoirs and summarize the logging response characteristics of different genetic types,which has laid the foundations for logging evaluation of low permeability sandstone reservoirs.The results show that the complexity of water concentration,lithology,logging environment are dominent factors resulting in the complexity of logging response characteristics.?2?The paper studies the characteristics of microscopic pore structure and its formation mechanism of Es₃x¹ in Zhuang62-66 area of Wuhaozhuang Oilfield according to the common slices,casting slices,physical property analysis and mercury injection curve data.The results show that compaction,cementation,dissolution and other diagenesis have significant impacts on pore throat characteristics.The calculation of parameters,such as apparent compaction rate,visual cem ent ratio,apparent dissolution rate visual micro porosity and so on,reveals that compaction,cementation and dissolution control quantitatively the pore structure characteristic parameters,such as median pressure,pore throat radius,tortuosity,homogen eous coefficient and so on.We further establish nonlinear fitting relationship between logging data and different rock forming mechanism parameters on the basis of BP neural network method,and also evaluate weight of different rock forming mechanism parameters which affect pore structure using grey correlation analysis method.Besides,factor Q has been put forward as a new evaluation index to evaluate pore structure,which has better correlation with pore structure characteristic parameters of mercury injection experiment.Finally,a set of methods to evaluate pore structure considering the microscopic formation mechanism has been established.?3?For the situation of strong heterogeneity and low calculating accuracy of the reservoir physical property parameters in low permeability sandstone reservoirs,the study introduces petrophysical facies into reservoir classification and establishment of logging interpretation models.Petrophysical facies comprehensively reflect the characteristics of lithology,physical properties and pore structure.We adopte fuzzy clustering analysis to divide petrophysical facies in the reservoirs of cored wells,using method named as core calibrating logging to extract logging response characteristics of all petrophysical facies.Besides,we divide the petrophysical facies in no coring well section using principal component analysis and to accomplish the hole well prediction of the physical properties based on lithofacies constraints.The interpretation accuracy has been improved greatly compared with the past and the method receives good effect in field application.?4?Taking Es₃x¹ in Zhuang62-66 area of Wuhaozhuang Oilfield as an example,to solve the problem that fluid identification is difficult in low permeability sandston e reservoirs,we study on the sensitive parameters reflecting the fluid properties using chart recognition technology,and create different cross-plots of sensitive parameters giving full consideration to the lithology,physical properties and characteristic s of formation water,we establish the cross-plots of oil layer versus water layer by enlarging the slight difference between them.Thus introduce modern mathematics geology methods into fluid identification,establishing a method for fluid identification based on Fisher discriminant analysis and good effects have been achieved.?5?Taking Quan 4 member reservoir of Rang 11 area in Jilin Oilfield as an example,we discuss the applications of logging data in qualitative identification of fractures and quantitative characterization of fracture parameters.Taking advantage of conventional log data as the main means,we establish a qualitative evaluation method for fracture classification based on fuzzy pattern recognition and a quantitative discrimination method based on synthetic probability index method,and accomplish evaluationg of the macrofractures developed in low permeability sandstone reservoirs by logging data from both qualitative and quantitative level.What's more,through the combined application of thin sections,casting thin sections,physical analysis and mercury injection data,we summarize the microscopic characteristics of microfractures and their impacts on the difference s of reservoir physical properties.On this basis,we propose a method of calculating characterization parameters of microfractures using concentrative function in low permeabilit y-tight sandstone reservoirs.As to the problems existing in the logging evaluation of low permeability sandstone reservoirs,relatively systematic analysis of ideas and solutions are put forward to provide technical support for logging evaluation of the c omplicated low permeability sandstone reservoirs.