The pore-throat structure is a critical factor in the study of unconventional oil and gas reservoirs, drawing particular attention from petroleum geologists, and it is of paramount significance to analyze to enhance oil and gas production. In tight sandstone, which serves as a significant hydrocarbon reservoir, the internal pore-throat structure plays a decisive role in the storage and migration of fluids such as water, gases, and hydrocarbons. This paper employs casting thin section (CTS), field emission scanning electron microscope (FE-SEM), high-pressure mercury injection (HPMI), and low-temperature nitrogen gas adsorption (LT−N₂−GA) experimental tests to qualitatively and quantitatively analyze the characteristics of the pore-throat structure in tight sandstone. The results indicate that the pore types in tight sandstone include intergranular residual pores, dissolution pores, intercrystalline pores, and microfractures, while the throat types encompass sheet-shaped, curved-sheet-shaped, and tubular throats. Analysis of the physical and structural parameters from 13 HPMI and 5 LT−N₂−GA samples reveals a bimodal distribution of pore-throat radii. The complexity of the pore-throat structure is identified as a primary controlling factor for reservoir permeability. The fractal dimension (D) exhibits an average value of 2.45, displaying a negative correlation with porosity (R² = 0.22), permeability (R² = 0.65), the pore-throat diameter (R² = 0.58), and maximum mercury saturation (R² = 0.86) and a positive correlation with threshold pressure (R² = 0.56), median saturation pressure (R² = 0.49), BET specific surface area (R² = 0.51), and BJH total pore volume (R² = 0.14). As D increases, reservoir pores tend to decrease in size, leading to reduced flow and deteriorated physical properties, indicative of a more complex pore-throat structure.

Utilizing well logging data, outcrop profiles, and previous research, this study analyzes the sedimentary and tectonic evolution of the Yan’an Formation in the Ordos Basin, correlating the resulting sedimentary facies with hydrocarbon reservoirs to establish the necessary connections. The study reveals that: (1) Vertically, the sediment grain size shows a pattern of coarser grains at the bottom and top, with finer grains in the middle. Horizontally, the grain size tends to become finer from the northern, western, and southern parts of the basin toward the central-western region. (2) Tectonic movements during the Yan’an period controlled the sedimentary environment. These tectonic activities, through uplift and subsidence, caused the Yan’an Formation to experience four stages of sedimentary environments: braided river, lake, delta, and meandering river. (3) The Yan’an Formation exhibits four types of reservoir sandbody stacking patterns—continuous superposition, intermittent superposition, interbedded sand-mud, and single sandbody types—with continuous and intermittent stacking being the most common. (4) The hydrocarbons in the Yan’an Formation originated from the Chang 7 Member of the Yanchang Formation and migrated into the Yan’an reservoirs. The oil is characterized by its low density, low viscosity, and low pour point, indicating it is a high-maturity, high-quality crude oil.

The sedimentary mechanisms and depositional processes of deep-water gravity flows in lacustrine basins remain incompletely understood, posing challenges for accurate reservoir prediction in continental rift basins. This study investigates the Triassic Yanchang Formation in the Ordos Basin to elucidate the genetic processes and evolutionary mechanisms of deep-lake gravity flow deposits. Through systematic core observations, grain size analysis (including mean size, sorting, skewness and kurtosis), and sedimentary facies analysis, we identified four distinct gravity flow types: (1) sandy debris flows, (2) muddy debris flows, (3) turbidity currents, and (4) slumps. Quantitative grain size parameters reveal significant differences among these facies, with mean grain size ranging from 1.19Φ to 3.53Φ. Three primary triggering mechanisms are recognized: seismic events (seismites), volcanic events (tuffaceous layers), and anoxic events ("Zhangjiatan" shales), with seismic and volcanic events exerting particularly strong influences. A new depositional pattern is proposed, detailing the complete evolutionary sequence from slope failure initiation to final deposition, encompassing the sliding-slumping-debris flow-turbidity current transition. This study advances understanding by: (1) establishing quantitative discriminators for different gravity flow types, (2) clarifying the causal relationships between external triggers and flow deposition, and (3) providing a comprehensive evolutionary framework for lacustrine gravity flow systems. These findings significantly enhance the ability to predict deep-lacustrine sedimentary architectures and hydrocarbon reservoirs, offering valuable insights for exploration in analogous rift basins.