Numerical Rock Construction And Pore Network Extraction

Pore-scale modeling, acting as an important study approach for unveiling the flow mechanism in porous media and exploring unknown flow patterns at pore scale, is now a hot research field in the international academic world. To perform pore-scale study, it is first necessary to construct the research platform, numerical rock and pore network. Therefore, we conducted an all-round study in the field of model-building for both of them. We first prepared the input data for numerical rock construction, which include micro-CT images, grain size distribution curves, etc. Then, we studied the model-building methodologies of both CT scanning, simulated annealing and process based simulation. With these methods, we constructed numerical rocks for our selected rock samples including a sand pack, two sandstone samples and one carbonate sample. We analyzed the microscopic properties of the pore structure with local porosity and local percolation functions, and also assessed the conductivity of the numerical rock with lattice Boltzmann method. The results show that the physical method of scanning rock samples with high-resolution CT scanner is a direct and most accurate way for numerical rock construction. And the process based method can also be used in the field of pore scale modeling. However, the simulated annealing method is not suitable for model-building as the constructed pore structure differs much from that of the real rock and thus it requires further development. Based on the algorithm developed by Lee, Kashyap and Chu for medial axis construction, we proposed a new work flow for pore network extraction from numerical rocks, in which we first built the medial axis of the pore space in numerical rock and removed its redundant branches contributed by the highly irregular matrix surface and then located the pores and throats and calculated their geometrical parameters afterwards. Our developed method can extract topologically and geometrically equivalent pore network from its mother numerical rock. With our constructed pore networks, we performed pore-scale modeling and studied the effects of potentially influencing factors on oil/water relative permeabilities, which include pore and throat size, coordination number distribution, contact angle and the initial water saturation. And this sensitivity analysis deepened our understanding about the influence of pore structure and wettability on fluid flow properties. We also predicted the absolute permeability of the pore network and the oil/water relative permeabilities. The good agreements between them and the statistical results from numerical rock as well as the physical experimental results validate the feasibility and reliability of our proposed methods for numerical rock construction and pore network extraction in this PhD project. Numerical rock and pore network work as the fundamental research platform for all the pore-scale study of flow through porous media, and thus they have important scientific and academic value as well as promising application prospect.