Fine Evaluation Of Fractures Based On CT Scanning Technology

Micro fractures are of great significance in the study of reservoir development,because micro fractures are the effective reservoir space and the main flow channel.In the process of reservoir exploitation,the pressure inside the reservoir changes dramatically due to the exploitation and operation.For fractured reservoirs,pressure changes have a severe impact on the flow capacity of fractures.Therefore,it is very important to study the stress sensitivity of fractures.According to its origin,micro fractures can be divided into natural micro fractures and artificially induced micro fractures.In this study,natural micro fractures and artificially induced micro fractures are studied respectively.Firstly,the digital cores of fractured rocks are acquired based on Computed Tomography(CT)technology.According to the magnification of lens(0.4X,4X and 10X),the core resolution has three levels(20 micron,4micron and 1.8 micron).Then,the fractures from different types of rocks are extracted,and the minimum aperture,average aperture and surface roughness of the fractures are measured.Based on the fractal theory,the fractal dimensions of digital cores of micro fractures are calculated.By Lattice Boltzmann Method(LBM)or finite element method,flow simulation can be carried out to calculate the permeability of each fracture.Further more,core-scale stress sensitivity experiment and micro-scale stress sensitivity experiment are carried out respectively,and cyclic stress sensitivity experiments are carried out on two cores,and then the changes of fracture aperture and permeability under different effective stress are quantitatively evaluated.The results show that CT scanning method has obvious advantages in constructing digital cores of micro fractures,and cores from tight sandstone,coal and carbonate have been obtained by CT scanning method.Through quantitative analysis and calculation,it is found that fracture permeability is closely related to three-dimensional(3D)fractal dimension,average aperture,minimum aperture and surface roughness of fracture.Stress sensitivity experiments show that there are turning points in both core-scale and micro-scale experiments.The second cycle of two cyclic stress sensitive experiments is studied separately,it is found that when confining pressure is reduced to 0 MPa,permeability can recover to a higher position than that of the first cycle.The results of this study can provide theoretical guidance for the development of fractured reservoirs.