Study On Well Logging Evaluation Method For Oil-bearing Property Of Lower Shihezi Formation In Gangbei Buried Hill

With the increasing attention to energy security in China,increasing oil and gas reserves and production has become an important goal of major oil fields.In recent years,the exploration focus of Beidagang Buried Hill Zone in Huanghua Depression has gradually shifted from low buried hill to middle and high buried hill.A new breakthrough has been made in the Carboniferous Permian target stratum in Gangbei Buried Hill.Among them,the clastic reservoir of Lower Shihezi Formation is a fluvial facies deposit with a large thickness and stable distribution of sand body,which is the main reservoir section of Permian.However,the Lower Shihezi Formation reservoir is low porosity and low permeability reservoir,which has the characteristics of small porosity,low permeability,complex reservoir space,and secondary pore development.There are many problems in the comprehensive logging evaluation,such as difficult calculation of reservoir parameters,difficult evaluation of saturation,difficult division of effective reservoir and difficult evaluation of fluid properties,which seriously restrict the effectiveness of oil and gas exploration.In this paper,the Lower Shihezi Formation reservoir in Gangbei Buried Hill of the Dagang Exploration Area is taken as the main research object.Firstly,the geological background of Gangbei Buried Hill is introduced.The basic characteristics of the Lower Shihezi Formation reservoir,such as lithology,physical property,oil-bearing property,are analyzed based on the geological data,logging data and core analysis data.On this basis,the four-properties relationship of the reservoir is analyzed in combination with well logging data.Secondary,in view of the complex lithology of the Lower Shihezi Formation,the lithology is classified by using the step by step lithologic identification method of multi curve intersection,and the mineral content is quantitatively calculated by using the multi mineral model of the three porosity curve.On this basis,the core experimental data are regressed to establish the shale content and permeability model,and the clay distribution form is analyzed to establish the porosity model.Based on the analysis of the results of the rock resistivity experiment,the important influence of the rock resistivity parameters on the oil-bearing evaluation of the low porosity and low permeability reservoir is recognized,and the oil saturation model with variable m and n values based on the Archie formula is determined.Finally,the effectiveness of the reservoir is evaluated by using the empirical statistics method and the chart method,and the evaluation standard of the fluid property is established by considering the influence of lithology comprehensively,forming a set of well logging evaluation method suitable for the low porosity and low permeability reservoir of Lower Shihezi Formation.The comprehensive interpretation and evaluation of the key wells in the study area are carried out by using the established well logging evaluation method,which is compared with the conventional interpretation results.The results show that the established well logging evaluation method can effectively improve the calculation accuracy of porosity,permeability,and oil saturation,and the coincidence rate of interpretation results is increased from 53.1% to 90%.It has a certain reference significance for the well logging evaluation of low porosity and low permeability reservoirs in the study area.