Research On Microcosmic Analysis And Fracture Prediction Of Carbonate Reservoirs, Renqiu Buried Hills

In recent years,carbonate fractured reservoirs of buried hills is an important research field on increasing production and reserve. In this paper,the carbonate reservoir of Renqiu buried hills in Jizhong depression is taken as an example,the geological background of crack formation,the microscopic characteristics,the distribution of crustal stress,the distribution of cracks and the factors which affect the development of the cracks were systematically and deeply researched. The concrete research contains basic experiment,theoretical research,numerical simulation and self-developed software. The main achievements are as follows:Firstly,the regional geology,reservoir features and tectonic evolution were analyzed by using field observation and other data. The space matching relationship between fractured structure and fracture was determined,providing basis for comprehensive research of fractures.Secondly,the microcosmic analysis of the reservoir was done by using various technologies such as scanning electric mirror, X-ray photoelectron spectroscopy ,fluorescence,Raman microprobe and infrared spectra. The fluid inclusions from Wumishan formation in Renqiu oilfield were tested and analyzed. On the basis of test data, palaeo-pressure of the reservoir was also calculated. Then core samples were analyzed and recognized in both space and spectrum. Especially,the experimental data from the system were processed and comprehensively studied by using data fusion technology of image spectral information. The distribution of different hydrocarbons in rock cores and the connectivity of pores were visually revealed,providing evidence for fracture prediction.Thirdly,based on the relationship between rock acoustic properties and mechanical properties,the effective model for the acquisition of rock mechanics parameters by using conventional well logging information was established. The type of probability distribution of rock elastic modulus and Poisson's ratio were researched,and the statistical characteristics was obtained.Fourthly,in consideration of the complicated multi-axial stress of carbonate reservoir and the coupling effect of geothermal field and crustal stress field,the crustal stress was systematically studied. The model which determined the distribution of the reservoir stress was derived by using the method of multi-objective optimization techniques. The distribution of principal stress and the fracture pressure of Wumishan Formation were obtained. The related curve of the principal stress versus the depth of researched area was obtained also. The research includes the maximum and the minimum horizontal principal stress,the maximum shear stress,the direction of the maximum and the minimum horizontal main compression stress,the index of fracture development etc. The results show that the numerical simulation is consistent with the actual measurements.Finally,the method of using Monte carlo random finite element simulation technology was proposed to predict and analyze the development of fracture in carbonate reservoirs. The shear and the broken fracture rate of the reservoir in the study area were calculated by using Mohr-coulomb and Griffith criterion. The result showed that the fitting relationship between the density and development index of the crack could better forecast and analyze the distribution rules of the fracture density. The self-developed software, named"Fracture of Carbonate Reservoir Analysis system", not only improved the efficiency,but also avoided personal errors. The transformation from the theoretical approach to the practical application was implemented.