Validating mechanistic models of fluid displacement during imbibition

Abstract

Pore-scale modelling is an important tool to improve our understanding of multiphase flow in porous media. Slow fluid invasion is commonly modelled using quasi-static pore network models (PNM). These models simulate the invasion in a network of simplified pores and throats by invading network elements in order of the quasi-static “invasion” capillary pressure it would take for the wetting phase to enter. Despite a multitude of studies that address the predictiveness of PNM, it remains unclear what the leading causes of errors in these methods are, particularly during imbibition. To address this, we developed a novel method to directly validate the invasion capillary pressure models that underly quasi-static PNM for the first time. The new method compares these models to local capillary pressures measured during in-situ flow experiments visualized with 4D micro-CT. We applied this to two different PNM extractions from a μCT dataset of a glass beads pack that underwent slow imbibition. This methodology is limited by the temporal resolution of the data, hence we tested assumptions regarding displacement sequences when individual displacements could not be resolved. To constrain the uncertainty on the input parameters, we used local contact angles measured from the μCT images. The model-predicted invasion-Pc values were on average greater than the direct measurements made using curvatures also extracted from the μCT images. Important sources of mismatch were the difficulty to accurately describe the pore space as a network of pores and throats, as well as the relatively low temporal resolution of the dataset. The method and results presented here can be used to direct the development of improved pore network models.

Correlations of residual oil distribution with pore structure during the water flooding process in sandstone reservoirs

“…The fluid invasion process during imbibition occurs as a combination of piston-like displacements, cooperative porefillings (characterized by I n , where "n" represents the number of surrounding throats filled with oil) and snap-offs (Ellman et al, 2024). As piston-like displacements do not change the connectivity of the oil phase, this work focuses on porefilling and snap-off.…”

“…Singh et al (2022) conducted a time-resolved tomographic drainage-imbibition experiment on a carbonate rock sample, and provided correlations for displacement events as a function of pore-throat geometry through pore-by-pore analysis. By combining experimental data with a pore network model, a work flow has been presented to investigate the relationships between pore structure and dynamic pore filling events (Ellman et al, 2024). It should also be noted that effect of pore structure is indistinguishable from that of local wettability or other factors, while the local flow conditions of a porous sample are hard to keep constant during the experimental process.…”