Volcanic Reservoir Logging Evaluation In West~SHG Qaidam Basin

Qaidam Basin is a large Mesozoic and Cenozoic continental petroleum bearing basin in Western China,the research area is located in the south of the western margin of qaidam basin,and the reservoir is mainly carboniferous.The lithology of Carboniferous volcanic rocks in the study area can be divided into three main categories:andesitic basalt,tuff and conglomerate.Volcanic reservoirs are mainly affected by lithofacies and lithology,the logging response characteristics of volcanic rocks are the comprehensive reflection of composition,structure,alteration,degree of pore development and fluid properties of rocks,combining logging data with other geological data to judge the rock facies and lithology characteristics is the key technology.Because of the complex mineral composition of volcanic rocks,the logging response characteristics of volcanic rocks are overlapped and interrelated,and the correlation is complex,it is difficult to identify volcanic rocks by logging data:Generally,the porosity of the volcanic reservoir matrix is small,and the high quality reservoirs often have cracks and holes,accurate calculation of matrix pores below 7% and evaluation of the effectiveness of cracks and holes has always been a difficult point in logging reservoir evaluation.The resistivity of volcanic rock reservoir changes greatly,the same lithology has different resistivity and different rock structure,the influence of rock block on resistivity is much greater than that of pore fluid,therefore,the traditional oil-bearing evaluation method is poor in adaptability,and the oil-water interface is difficult to determine,so we need to find new breakthroughs.In the course of the study,based on the previous research foundation of the exploration and development research institute,using the(CPL)logging data and geological data,through the comparative analysis of logging data and geological data,this paper obtains the lithology classification and lithology identification standard,and makes clear the division and distribution law of the study area.On the basis of lithologic identification and petrographic division,through the analysis of the relationship between the four properties,the formation of the oil layer plate,the identification and study of the distribution of the cracks and the identification of the fluid properties,the fine evaluation of the reservoir is achieved.The main technical methods in the research process include the following aspects:(1)Logging data from drilling coring,rock slice and imaging logging are used to calibrate conventional logging,and a lithology identification chart based on conventional logging data is established.On the basis of dividing the single well rock,the horizontal lithologic profile and the plane dominant lithofacies map can be used to solve the lithology division problem in the area of the study area,and provide reliable lithologic base data for the reserves calculation;(2)Combined with the core material,using the imaging logging data to determine the main fracture type,the direction of the maximum principal stress and the effectiveness of the crack in the study area,and quantitatively calculate the porosity of the fracture.By using image and core data to calibrate conventional logging,the model of calculating fracture porosity by conventional logging method is established,and the response characteristics of crack in conventional logging are clarified.(3)Lithology and block blocks are used to evaluate the productivity of the reservoir in the work area,and the results show that the single well production in the conglomerate reservoir is the highest.In addition,due to the influence of the distribution of dominant rocks,the most productive contribution of lion 101 well is tuff,and the largest contribution of the zone in the second exploration area is the conglomerate reservoir.Under the same lithofacies,the yield of single well is controlled by the degree of fracture development and the effectiveness of fracture,the higher the degree of fracture development and the better the effectiveness of the fracture,the higher the yield of the single well.(4)According to the comprehensive analysis and research of logging,coring,laboratory analysis and oil production test,the parameter chart of reserves calculation is made.To sum up,the above method can effectively predict the lithology and lithofacies characteristics of the volcanic reservoir,identify the distribution of cracks and fluid,and provide a powerful technical support for the calculation of new proven reserves in the reservoir.