Impacts of the Pore–Throat Structure on Fluid Mobility in Tight Sandstone: Insight from an Improved Method Based on Rate-Controlled Porosimetry and Nuclear Magnetic Resonance

Abstract

The microstructure of pores strongly influences fluid mobility in tight sandstone reservoirs. The impacts of the pore–throat structure on fluid mobility are restricted due to the limitations of existing methods for determining pore–throat structures. Therefore, the methods utilized to obtain more comprehensive and accurate pore–throat information need to be further discussed by combining multiple experiments. In this research, eight samples were selected from the Upper Triassic Yanchang Formation in the Ordos Basin to investigate the microstructure and its impacts on fluid mobility by means of nuclear magnetic resonance (NMR), rate-controlled porosimetry (RCP), scanning electron microscopy, and thin sections. The throat radii in the throat, pore–throat, and pore areas were studied by combining NMR and RCP with an improved method. The throat radius and pore–throat volume affect the movable fluid from connectivity and movable ratio, respectively. The throat and pore–throat (pore) areas belong to unrelated movable fluid networks. Each area contains intragranular and intergranular spaces. Irregularly shaped pores commonly occur in the intragranular space, with strong connectivity. The pores with regular shape in the intergranular space connect a small amount of throat, and a large number of clay minerals divide the space into small throats. Clay minerals reduce fluid mobility by increasing the thickness of the water film in the throat. Therefore, fluid mobility in the intragranular space is greater than that in the intergranular space from the perspective of water film thickness and movable probability in the same area. This research improves the accuracy of the combined method of NMR and RCP and clarifies the distribution mechanism of movable fluids in different spaces.

Microscopic Mechanism of CO2 Displacement Oil in Different Pore Throat Radius Segments of Tight Sandstone Reservoirs

“…The HPMI method cannot effectively reflect information on corresponding connected pores below the maximum pressure required for mercury intrusion. Conversely, the T 2 spectrum of water-saturated pores can represent the total pore-throat information in the core. , The combination of HPMI and NMR has been utilized to comprehensively describe the full pore size distribution (Figure ). The deficiency of an extensive description of the pore throat scale arising from the limitation of mercury intrusion was overcome by establishing a fitting relationship between the pore throat radius and transverse relaxation time ( T 2 ).…”

Quantitative characterization of the carbonate rock microstructure considering topological features: a case study from the Gaoshiti–Moxi block of the Sichuan Basin

“…The NMR technique is widely applied to the analysis of pore structures (Golsanami et al, 2019;Yan et al, 2019;Ouyang et al, 2023) and is especially useful for analyzing rock/fluid interactions (Ali et al, 2022;Isah et al, 2022;Wang et al, 2023), despite its limitations. The experiments were conducted at the China University of Petroleum (East China).…”