Log Evaluation Method Of Tight Oil Reservoir In S4 Formation Of Damintun Sag

With exploration and development in oilfield, complex reservoir has gradually became the main source of oilfield to increase reserve and production. Tight oil reservoir in S4 Formation of Damintun sag has the characteristics of low porosity and low permeability, various lithology, complex pore structure, shaliness and high irreducible water saturation, which enhance the difficulty for further lithology identification and saturation calculation.Based on petrophysical experiment and well logging data, the characteristics of lithology, physical property and pore structure in the block have been studied by statistical methods. The results indicate that the reservoir is the tight reservoir with various lithology, poor petrophysical property and complex pore structure. Based on the geological characteristics and log responses of the different lithologies in the block, the lithologies can be divided into three kinds, including oil shale, siltstone and argillaceous dolomite. By means of statistical methods, the sensitivity of logging curves for lithology identification has been analyzed, by which reservoir transit time, density and gamma ray have been optimized. After that log response cross plot, decision tree model and quantum neural network model have been established to determine the lithology of the tight oil reservoir with selected sensitive log responses. The results indicate that decision tree model and quantum neural network model which based on data mining method show better recognition accuracy than conventional log response cross plot. According to core analysis data and logging data, the parameters interpretation models are established to calculate shale content, porosity and other parameters of the three kinds of reservoirs. Based on petrophysical experiment data and the characteristics of the three reservoirs, the conductivity model of tight sandstone reservoir is established by modified equivalent rock element theory and generalized Archie law, the conductivity model of argillaceous dolomite reservoir is established by connectivity equation and mixing law, and the conductivity model of oil shale is established by effective medium conduction theory. On the base of three models, the sensitivity of parameters has been analyzed, the parameters have been determined by petrophysical experiment data and and well logging data, and water saturation solution methods have been given in this paper. After that, the logging data of tight sandstone reservoir, argillaceous dolomite reservoir and oil shale in S4 Formation of Damintun Sag are processed and interpreted with the proposed models, and the results show that the models can be well applied in log interpretation for the tight oil reservoir in S4 Formation of Damintun sag.