Log Interpretation And Evaluation Methods For Complex Lithologic Reservoirs In North Of Wuerxun Area,Hailaer Basin

Logging interpretation and evaluation of complex lithologic reservoirs has always been a difficult problem in the global oil and gas exploration.Because of the changeable lithology,the responses of the logging curves is irregular.The method of interpretation generally has some regional characteristics,which cannot be used to other regions.The Hailar basin is a combination of two types of closing to sediment source and long-term transport deposits.The rocks formed by the rapid accumulation of closing to sediment source materials are complex and changeable with very poor separation,and there are great differences in composition and structure.There are many kinds of pyroclastic rocks in the north of Wuerxun Depression in Hailar basin,which have the characteristics of complex lithology,low porosity and poor permeability,large changes in the salinity of the formation water,which makes the logging interpretation and evaluation difficult and the interpretation coincidence rate is only about 70%.The degree of exploration in the north of Wuerxun Depression is low.There are several problems in the process of logging evaluation.One is that the volcanic clastic rock and terrigenous clastic rock exist at the same time,rocks being various with transitive lithology,while the mineral composition is complex and changeable with great changes in contents.Due to the complex lithology of the reservoir,it is difficult to identify the lithology accurately with well logging data.As a result,determining the parameters of the rock skeleton is hard and the accuracy of the porosity calculation is influenced accordingly.Secondly,the oil-water relations are complex in the reservoir in which low resistivity oil and high resistivity water exist.And the range of salinity varies from 5000 to 39000 PPM.The logging responses are subject to lithology,physical properties and water.It is difficult to identify fluid properties considering all the related factors.Thirdly,the previous research work of logging interpretation is not thorough and adequate.Lacking in logging information which are supposed to be collected,complex reservoirs cannot be clearly identified.Therefore,it is of great significance to carry out the well logging interpretation and evaluation research in the Wuerxun Depression and establish a set of appropriate logging evaluation criteria for the future exploration and exploitation of the oil field.Based on previous literature surveys,this paper involves the research of logging interpretation and evaluation methods in several aspects,which are regular analysis,the identification of lithology,calculations of reservoir parameters,model establishment,identification of fluid properties and the classification of reservoirs using conventional logging,nuclear magnetic logging,core analysis,clay analysis,thin slice and oil test data.It is found that(1)there are mainly argillaceous siltstone,fine sandstone,siltstone,gravel and coarse sand rock in the north of Wuerxun Depression,in which siltstone,coarse sandstone and argillaceous siltstone have good physical properties.Compared with the first section,the physical properties and oil content in the second section of the Nan Tun formation are better with higher porosity and permeability while the distribution is more concentrated.(2)the lithology is identified by the GR-XN-D rendezvous method.The boundary is obvious and the result of classification is very good.Based on the above,the FEAT element logging method is added to the identification of the reservoir.Considering the difference in mineral composition,the high resistivity mudstone layers can be effectively identified,while avoiding the interference in the division of reservoirs caused by high-resistivity mudstones.(3)six methods have been tried in the calculation of porosity,in which the skeleton calculation method,the fitting and regression of three curves and the NMR method have the best results,and the applicable conditions are summarized.(4)the identification chart of oil and water layers was established in the study area according to the degree of mineralization.(5)using core analysis data and conventional logging data,the reservoir classification charts are set up respectively.Aiming at the research area,the reservoirs are divided into four categories: I,IIA,IIB and III reservoirs,and the coincidence rate of the plate is over 90%.The completion of this paper provides a practical method for the analysis of reservoir characteristics,lithology identification,the establishment of reservoir parameter model,fluid identification,reservoir classification and the establishment of interpretation standards.It can serve as a rammed base in the process of well logging interpretation in the exploration and exploitation of volcanic clastic reservoirs in the north of Wuerxun depression.