Study On Lithologic Identification And Fracture Evaluation Of Igneous Rock Reservoirs

Igneous rock reservoir is arousing more and more attention as one kind of peculiar reservoir,especially in the current of oil/gas reserves and output dropping.But the complex of anisotropy and difficulty of exploration of igneous rock reservoir far exceeds others. In the paper,two difficult problems are studied. One is lithologic identification,which is a basic work in reservoir evaluation. Enhancing coincidence rate of lithologic identification is still challenging problem.The other is fracture evaluation,which is the key to reservoir evaluation,for fracture is the most important conditions for the store and exploitation of the oil/gas.By analyzing the chemical composition and mineral combination and summarizing the character of log response,according to the characteristic of Xin-jiang and Da-qing,using the log crossplots and neural network to identify the lithology in Xin-jiang oil field is satisfactory,so dose the TAS in Da-qing.Analyzing the characteristics of the different;logging response to fracture,researching fracture identification methods,making use of conventional log,diplog and imaging log to identify fracture qualitatively,even semi-quantitatively.Studied the mud invasion characteristics of fractured igneous reservoirs,dual laterolog response mechanism is emphasized.According to dual porous media model and different distribution of oil and water,the formula of computing fracture porosity is obtained.On the basic of the results,utilizing the improved 3D-finite element method,simplifying the parallel fractured model,based on the equivalence between response of a medium with parallel fractures of equal spacing and that of a macroscopically anisotropic medium,researching with numerical simulation,the functional relationship between the response and the physical parameters of the fractured formation are set up in the condition of different matrix resistivity.Two sets of formula for the estimation of fracture porosity are presented perfectly,among which one for manual application,the other for computer.Well-logging data of igneous in Xin-jiang and Da-qing oil field have been interpreted with the program developed which is based on the model mentioned above.The results indicate that this method and formula have a good effect on evaluating fracture parameters in igneous reservoir.