Abstract
The simulation of various rock properties based on three-dimensional digital cores plays an increasingly important role in oil and gas exploration and development. The accuracy of 3D digital core reconstruction is important for determining rock properties. In this paper, existing 3D digital core-reconstruction methods are divided into two categories: 3D digital cores based on physical experiments and 3D digital core stochastic reconstructions based on two-dimensional (2D) slices. Additionally, 2D slice-based digital core stochastic reconstruction techniques are classified into four types: a stochastic reconstruction method based on 2D slice mathematical-feature statistical constraints, a stochastic reconstruction method based on statistical constraints that are related to 2D slice morphological characteristics, a physics process-based stochastic reconstruction method, and a hybrid stochastic reconstruction method. The progress related to these various stochastic reconstruction methods, the characteristics of constructed 3D digital cores, and the potential of these methods are analysed and discussed in detail. Finally, reasonable prospects are presented based on the current state of this research area. Currently, studies on digital core reconstruction, especially for the 3D digital core stochastic reconstruction method based on 2D slices, are still very rough, and much room for improvement remains. In particular, we emphasize the importance of evaluating functions, multiscale 3D digital cores, multicomponent 3D digital cores, and disciplinary intersection methods in the 3D construction of digital cores. These four directions should provide focus, alongside challenges, for this research area in the future. This review provides important insights into 3D digital core reconstruction.
Highlights
With continuous exploration and development in the petroleum industry, unconventional reservoirs, such as tight oil and gas, shale oil and gas, coalbed methane, and natural gas-hydrate reservoirs, have received more attention than conventional oil and gas reservoirs; these unconventional reservoirs are becoming key areas for exploration and development [1,2,3,4,5,6,7,8,9,10]
Rock imaging methods based on a serial section rock overlay are destructive imaging techniques, of which two exist: the ordinary sequence 2.1. Ordinary Sequence Two-Dimensional (2D) slice superposition method and the focused ion beam scanning electron microscopy (FIB-SEM) physical imaging method [46, 47]
The resolution can reach the nanoscale based on the rock serial section overlay imaging method, the FIB-SEM technique is problematic because it destroys rock samples and has a slow modelling speed (Figure 2)
Summary
With continuous exploration and development in the petroleum industry, unconventional reservoirs, such as tight oil and gas, shale oil and gas, coalbed methane, and natural gas-hydrate reservoirs, have received more attention than conventional oil and gas reservoirs; these unconventional reservoirs are becoming key areas for exploration and development [1,2,3,4,5,6,7,8,9,10]. For virtual rock physics research that uses digital cores, guaranteeing the accuracy in a simulation experiment is based on the accuracy of modelling the numerical core. The abovementioned numerical core models simplify the pore space of the rock, so accurately reflecting the characteristics of unconventional reservoirs is difficult. Physical methods are employed to directly reconstruct 3D digital cores; that is, the real structure of the rock samples is obtained by 3D scanning or continuous slice scanning with instruments and various other physical means. Three main physical experimental methods are used to create 3D digital cores: confocal laser scanning, serial section imaging, and X-ray CT scanning. Confocal laser scanning is not widely used in practical research
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