Effects of the Sandstone Pore Structure on Spontaneous Imbibition: A Systematic Experimental Investigation Based on Fractal Analysis

Abstract

Pore structure is one of the most fundamental properties in reservoir characterization and is closely related to spontaneous imbibition recovery. This work utilized tight sandstone reservoir rock samples in the Ordos Basin to probe the influencing factors of the pore structure and fractal characteristics on imbibition efficiency. A series of experiments including high-pressure mercury injection (HPMI) and low-pressure nitrogen gas adsorption (LP-N 2 GA) were performed to systematically characterize the pore structure of the tight sandstone rocks. Then, the effects of pore structures and fractal dimensions on the imbibition recovery factor were elaborately discussed. These factors were further ranked using the gray correlation analysis. Results indicated a relatively high imbibition recovery, which ranged from 64.91 to 89.88%. Mesopores were more conducive to gas production, accounting for up to 56.88%. The combination of HPMI and LP-N 2 GA data synergistically characterized pores in the entire range, from micro-to macropores of the subjected reservoir (0.02-10 μm). Sensitivity analyses showed that imbibition recovery correlated with the homogeneity coefficient, reservoir quality index, skew coefficient (S kp ), sorting coefficient (S p ), micropore volume, displacement pressure, specific surface area, and Swanson parameter. Additionally, the gray correlation analysis further suggested that imbibition efficiency was highly related to the fractal dimension, and gas production recovery was mainly governed by the mesopore fractal dimension. This work provides insights into how the pore structure affects spontaneous imbibition efficiency in tight sandstone reservoirs from a fractal perspective.

Spontaneous Imbibition and Evaporation in Rocks at the Nanometer Scale

“…The multiphase flow processes that take place within the porous rocks during injection and extraction largely determine the efficiency of gas storage. 4 The displacement dynamics of fluids in porous rocks are controlled by fluid properties, as well as by the structural and chemical properties of the rock, 5,6 which can vary significantly across length scales. 7 At the solid−fluid interfaces, molecular interactions between the rock and fluids determine the wetting state of the system.…”

“…The displacement dynamics of fluids in porous rocks are controlled by fluid properties, as well as by the structural and chemical properties of the rock, , which can vary significantly across length scales . At the solid–fluid interfaces, molecular interactions between the rock and fluids determine the wetting state of the system.…”