Research Progress of Microscopic Pore–Throat Classification and Grading Evaluation of Shale Reservoirs: A Minireview

Abstract

The grading evaluation of shales helps in understanding the shale reservoir formation and sweet-spot screening of physical properties. Reservoir formation of shale is closely related to the size, distribution, and connectivity of shale pore−throats. Therefore, characterization and classification of microscopic pore−throats are the basis for shale reservoir grading. However, previous microscopic pore−throat classification schemes for materials science are unsuitable for shales with strong heterogeneity. In recent years, the author's team has proposed a new classification method for microscopic pore−throats of shale reservoirs based on the comprehensive characterization of numerous shales with varied maturities in different basins. Results show that the microscopic pore−throats for all shales can be divided into micropores, small pores, mesopores, and macropores. The component, size, and distribution of microscopic pore−throats in shales in different basins differ due to the differences in mineral composition and diagenetic evolution of shales caused by varying depositional environments and burial histories. Correspondingly, the demarcation points of different types of pore−throats are different. After clustering statistical analysis of different types of microscopic pore−throats, shales can be divided into grade I, II, III, and IV reservoirs, regarded as good, medium, poor, and nonshale reservoirs, respectively. Grading evaluation criteria for shale reservoirs were then established. Further, a new technique for evaluating the reservoir flow zone index (FZI) and dividing flow units based on logging data was constructed using the relationship of permeability with porosity in the same hydraulic flow unit. The grading evaluation criteria can be applied to single wells, multiwells, and planes using logging data. The application in numerous shale oil and gas exploration areas in China shows that the established classification scheme can be applied to the grading evaluation and sweet-spot screening of shale reservoirs.

Quantitative evaluation of reservoir quality of tight oil sandstones in chang 7 member of Ordos Basin

“…Rock composition, pore type, pore size, fracture development and the matching relationship between these parameters are important factors for whether a tight oil reservoir can become an effective reservoir. How to define the main controlling factors of reservoir quality on the basis of petrophysical research is an important content of logging evaluation of tight sandstone reservoirs (Zhang et al, 2018;Li et al, 2019;Fan et al, 2022;Li H. et al, 2022;Li, 2022;Lu et al, 2022). Therefore, in this paper, the evaluation of rock composition and pore structures is selected as the core of reservoir quality evaluation.…”

Advances in Microscopic Pore Structure Characterization of Fine-Grained Mudrocks

“…Therefore, multiple characterization techniques are often needed to validate and complement each other. 23 However, different techniques are generally based on different assumptions, experimental conditions, theory models, and data interpretation methods, which need to be systematically summarized.…”

“…These techniques primarily include scanning electron microscopy (SEM), computed tomography (CT), low-temperature gas adsorption, fluid invasion porosimetry (FIP), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), spontaneous imbibition (SI), (ultra)­small-angle neutron scattering ((U)­SANS), and (ultra)­small-angle X-ray scattering ((U)­SAXS). ,− Unfortunately, the pore structure is difficult to quantify due to its nanoscale size, complex origin, distribution, and assembly, as well as strong heterogeneity. Therefore, multiple characterization techniques are often needed to validate and complement each other . However, different techniques are generally based on different assumptions, experimental conditions, theory models, and data interpretation methods, which need to be systematically summarized.…”

Novel Method for the Classification of Shale Oil Reservoirs Associated with Mobility: Inspiration from Gas Adsorption and Multiple Isothermal Stage Pyrolysis

“…22,29 Anomalously, subsequent publications yielded different categories, e.g., micropores, transitional pores, mesopores, and macropores corresponding to <30, 30−200, 200−1500, and >1500 nm, 30 or to <5, 5−50, 50−500, and >500 nm, respectively (Figure 1C−H). 24 Collectively, the pore division method for shale oil reservoirs based on high-pressure mercury injection needs to be further discussed. Establishing a suitable pore size classification for shale oil reservoirs, especially considering the occurrence state of oil molecules, is urgent and important.…”