High heterogeneity and small pore throat characterize the mineral compositions of complex reservoirs. The evaluation of the effectiveness of reservoir space, the detailed evaluation of the rock structure, and the evaluation of fluid occurrence and migration all determine the possibility of oil and gas exploration within complex reservoirs. The technologies and workflows used for the multi-scale digital rock evaluation of complex reservoirs analyze the reservoir space (i.e., the pore throat and fractures), the rock structure (i.e., mineral and organic matter), and fluid characteristics. For the reservoir space, two-dimensional large-area analysis is sufficient to evaluate heterogeneity and multi-scale selection across 6–7 orders of magnitude. Three-dimensional space distributions of pore throat and fractures are precisely depicted through a combination of multi-scale CT and FIB-SEM. The developing agent facilitates the analysis of the micro-pore connectivity effectively. For the solid components, a quantitative evaluation of mineral composition and distribution is possible using Qemscan, and organic matter morphology and distribution are quantitatively assessed using the three-dimensional FIB-SEM. To characterize the fluid, charging effects may aid in the identification and characterization of residual, organic fluid traces. We perform the physical modeling of shale oil occurrence and migration by using nano materials that have adjustable pore sizes, adjustable wettability, and adjustable surface microstructure to understand the impact that each factor has on shale oil occurrence and the lowest pore sizes in which fluid can migrate. We use molecular simulations to observe oil and gas aggregation mechanisms and the diffusion potential in inorganic and organic nano pores. To supplement the conventional reservoir analysis, multi-scale digital rock evaluation, and its specific applications, provide technical proof for effective complex reservoir assessment, including shale oil and gas reservoirs, tight sandstone oil and gas reservoirs, and deep oil and gas reservoirs, as well as a quantitative oil-gas probability evaluation.

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