Abstract
Unconventional rocks such as tight sandstone and shale usually develop multiscale complex pore structures, with dimensions ranging from nanometers to millimeters, and the full range can be difficult to characterize for natural samples. In this paper, we developed a new hybrid digital rock construction approach to mimic the pore space of tight sandstone by combining X-ray CT scanning and multiple-point geostatistics algorithm (MPGA). First, a three-dimensional macropore digital rock describing the macroscopic pore structure of tight sandstone was constructed by micro-CT scanning. Then, high-resolution scanning electron microscopy (SEM) was performed on the tight sandstone sample, and the three-dimensional micropore digital rock was reconstructed by MPGA. Finally, the macropore digital rock and the micropore digital rock were superimposed into the full-pore digital rock. In addition, the nuclear magnetic resonance (NMR) response of digital rocks is simulated using a random walk method, and seepage simulation was performed by the lattice Boltzmann method (LBM). The results show that the full-pore digital rock has the same anisotropy and good connectivity as the actual rock. The porosity, NMR response, and permeability are in good agreement with the experimental values.
Highlights
Looking around the world, with the depletion of conventional fossil energy, unconventional hydrocarbon resources will be the most realistic resource type in this change [1]
In this work, based on the hybrid method combining physical experiments and numerical reconstructions, we further develop a new combination method that integrated macropores constructed by X-ray Computerized tomography (CT) and micropores reconstructed by multiple-point geostatistics algorithm (MPGA)
We proposed a new strategy by combining the X-ray CT scanning method and multiple-point geostatistics algorithm (MPGA) in digital rock
Summary
With the depletion of conventional fossil energy, unconventional hydrocarbon resources will be the most realistic resource type in this change [1]. Unconventional reservoir rock is usually characterized by low porosity and permeability, fine pore throat, complex pore structure, and developed fracture network [5,6,7], the laboratory experiment is difficult to carry out, and the routine rock modeling methods such as capillary model are hard to describe the true and microscopic structure of unconventional rocks In face of these challenges, digital rock technology is currently expected to be the key to solve the above puzzles in unconventional reservoirs. Compared with the physical experiment method, the numerical reconstruction method has the advantages of low cost and high efficiency and can reconstruct different types of digital rocks. In this work, based on the hybrid method combining physical experiments and numerical reconstructions, we further develop a new combination method that integrated macropores constructed by X-ray CT and micropores reconstructed by MPGA. We utilized micro-CT to image the macropore structure of tight sandstone and constructed the macropore digital rock and used the SEM to image the micropores of tight sandstone and reconstructed the micropore digital rock using MPGA. rough the superposition of micropore and macropore digital rocks, the full-pore digital rock of tight sandstone was obtained, and the physical properties and seepage characteristics of the digital rocks were compared and analyzed
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