Well Logging Evaluation Methods For Complex Low Permeability Oil And Gas Reservoir

Low-permeability oil and gas reserves account for a large proportion in oil and natural gas geological reserves in china. Problem and routine were analyzed and depicted in log evaluation of low-permeability oil and gas reserves by analyzing Qinghai Youquanzi oil field, Jianshan oil field, Jaingsu Lianmengzhuang oil field, Jilin Honggang and Qianan gas field.Through the combined application of geology, logging, development and analysis of laboratory data, systematic analysis of genesis of the low-permeability reservoir was carried through from the sedimentation, diagenesis and the role of structure. Sedimentation controls the type of sediment, which is the decisive factor of the formation of low-permeability reservoir. Compaction and cementation can significantly reduce reservoir primary porosity; Based on analysis of genesis of the low-permeability reservoir, the characteristics of low-permeability reservoir was summed up. The result shows that fine granular sediments, complex lithology, various types of reservoir space, large numbers of micro-cracks, Strong non-homogeneous, poor and uneven distribution of oil-bearing are characteristics of low-permeability reservoir.The problem of low-permeability reservoir log evaluation are mainly dealing with the following issues: serious mud additional conductivity, various response characteristics of lithologic logging, serious mud invasion in drilling, interbedded thin stratum serious impact on characteristics of log responses, difficulty to identify crack and outstanding multiple solutions of logging. Based on above question, logging response mechanism of low-permeability reservoir was analyzed roundly from lithologic characteristics, formation water salinity, formation thickness, pore structure characteristics and mud invasion and low-permeability reservoir is divided into 3 types:fine-grained low-permeability reservoir, complex–lithologied low-permeability reservoir and fractured low-permeability reservoir. Also causes and formation environment, difficulty and counterm easures were analyzed of each type of low-permeability reservoir.To log evaluation of low-permeability reservoir, influencing factors and getting solution of physics parameters and characteristics of electric parameters of rocks under the conditions of complex reservoir space were analyzed. To improve the accuracy of log evaluation, reservoir physics should establish different models according to geological features, reservoir classification and the characteristics of dynamic production. Also the formation oil saturation was calculated out by using variable parametered Archie formula.The main geological significance, influencing factors and application of environmental of various composite geological parameters which are used to identify oil, gas and water were analyzed in low-permeability reservoir. The result shows that using crossplot of composite geological parameters to identify oil, gas and water of low-permeability reservoir can improve the interpretation accuracy greatly.New logging technologies to identify and evaluate low resistivity reservoirs were brought forward. FMI, Array Induction, NMR and ECS logging have great advantages on identify and evaluate low-permeability reservoir. The deep detection of Array Induction can overcome the impact of invasion and the good characteristics of profile invasion are very important to determine the type of fluid. Pore structure and irreducible water saturation gained from NMR is the most powerful tool to identify and evaluate high irreducible water saturation reservoir. FMI logging can identify lithology and reservoir cracks, so has important applications in complex lithologied and fractured low-permeability reservoir. ECS logging can provide full rich and quantitative lithology information.