Micro-Scale Pore-Throat Heterogeneity of Tight Oil Sandstone Reservoirs and Its Influence on Fluid Occurrence State

Abstract

Quantitatively characterizing the micro-scale heterogeneity of pore throats in tight sandstone reservoirs is the key to accurately describing the influence of pore structures on fluid occurrence characteristics. In this study, taking the Chang 6 Member of the Yanchang Formation in the Huaqing area of the Ordos Basin as an example, the pore-throat heterogeneity of tight sandstone reservoirs and its influence on the fluid occurrence state have been systematically studied using cast thin section, scanning electron microscope, X-ray diffraction, constant velocity mercury intrusion, and nuclear magnetic resonance tests. The main types of pores developed in the target layer were intergranular pores, followed by feldspar dissolution pores. The radius distribution of the intergranular pores is between 5.0 and 210 μm, with an average value of 50.27 μm. In addition, the pore combination types with the best petrophysical properties are the intergranular pore type, the intergranular-dissolution pore type, and the dissolution-intergranular pore type; the average permeability and porosity are 0.62 mD, 0.40 mD, 0.44 mD, and 12.0, 12.3, 12.3%, respectively. The target sandstones contain four typical T2 relaxation time types. The large-pore-fine-throat combination reservoir has the best petrophysical properties. The larger the pore-throat uniformity value, the more uniform the pore-throat radius, and the greater the reservoir permeability. Therefore, the uniformity of throat development controls the seepage capacity of the tight reservoirs. The movable fluid saturation of different pore types has obvious differences. The movable fluid saturations at the 0.1 and 0.5 μm pore diameters of the macro-pore-fine-throat and macro-pore-micro-throat reservoirs both show an obvious inflection point, and the movable water saturation is higher with a larger throat radius.

Characterization of fractures in low‐permeability thin tight sandstones: A case study of Chang 6 Member, Yanchang Formation, western Ordos Basin

“…A large number of intra‐grain dissolved pores of feldspar are developed in the Chang 6 Member, and dissolution occurs mostly along cleavage joints. Therefore, the intragranular dissolved pores have good pore connectivities, but they are only distributed in local reservoirs (Guo et al, 2022; Zeng et al, 2021).…”

Effect of Pore Structure Heterogeneity of Sandstone Reservoirs on Porosity–Permeability Variation by Using Single–Multi-Fractal Models

“…showed a negative linear correlation between fractal dimension and porosity/permeability. However, different from the single fractal model, the multifractal model could be more accurate for the study of PFDH. − Relevant research has proved that pore fractal features of tight sandstone have multiple fractal structures for different pore diameters. − …”

The Influence of Micro-Heterogeneity on Water Injection Development in Low-Permeability Sandstone Oil Reservoirs

“…Pore heterogeneity describes the variance in the type, size, distribution, and degree of sorting of pores and throats in rocks. These features can be quantitatively detailed using pore structure parameters such as the maximum pore radius, median pore radius, maximum connected throat radius, median throat radius, minimum-flow throat radius, and others [13][14][15]. Particle heterogeneity refers to the variance in particle size, shape, sorting, arrangement, and contact relationships.…”