Three-Dimensional Reconstruction Of Microscopic Pore Structure In Low-Permeability Reservoir

Due to the complexity of the reservoir rock microscopic pore structure, the studies of the equivalence of the rock pore structure to the pore network models as well as the pore-scale flow, which are the current international academic research hot spots, are of great significance. Digital core and pore network models are the basic platform for conducting the study of the pore-scale flow simulation. Aiming at the low-permeability gas reservoirs, this paper have conducted the study of the microscopic pore structure 3D reconstruction, adopted the CT scanning method to establish the digital cores of the real cores, built the pore network model equivalent to the digital cores by the pore network extraction method that is based on the maximal ball and predicted the porosity and permeability of the pore network model by the pore-level flow simulation theory and method.Through researches above, this paper mainly has got following understandings:(1) The CT scanning method, possessing advantages of high accuracy and no destroy to the original cores, is an effective physical experimental method for construct digital cores. And the modeling quality mainly depends on the scanning accuracy of the CT machine.(2) Based on the two-dimensional median filtering algorithm, this paper has presented the three-dimensional median filtering algorithm which can well remove the system noise in the image filtering processing, making the transition of the pore and the rock matrix in images natural, the gray level distribution interval more obvious, being favorable to divide the pore and the rock matrix as well as to get rid of most isolated pore and rock matrix.(3) The REV analytical method based on the cube porosity, and the two-point correlation function both can measure the REV size of digital cores. By comparing the digital core size with the REV size, the digital cores that can represent the rock pore structure and macroscopic properties can be selected, making the subsequent flow simulation study with physical meaning.(4) The pore network extraction method based on the maximal ball can effectively divide the pore space into the pore and the throat, establish the pore network model equivalent to the digital core, and keep the topological structure and the geometrical characteristic of digital core pore space.(5) The comparison of core pore structure parameters determined by the real core capillary pressure data with the pore network parameters, as well as the Fractal characterization contrast of the experimental pore structure parameters with model pore structure parameters can well evaluate the accuracy of the pore network model.(6) The microscopic flow simulation study based on the pore network model has been conducted to predict the porosity and the absolute permeability of the pore network model, the prediction results are highly consistent with the analysis results of the digital cores as well as the experimental results of the real cores, further improving the accuracy of the pore network model. Meanwhile, the oil-water and gas-water relative permeability in the water flooding process are predicted by the pore network model, and the prediction results accord with the characteristics of the relative permeability curve, demonstrating the accuracy of the prediction results with certain reference value.Researches show that the microscopic pore structure 3D reconstruction study aiming at the low-permeability gas reservoirs is successful with important academic value, providing a solid foundation for the subsequent microscopic flow rule study and EOR technology study, presenting new research thought and technical methods for the analysis of unconventional reservoirs.