EXTREME CAPILLARY HETEROGENEITIES AND IN SITU FLUID COMPARTMENTALIZATION DUE TO CLUSTERS OF DEFORMATION BANDS IN SANDSTONES

Abstract

Previous work has shown that individual deformation bands act like capillary barriers and influence fluid saturation. More common in nature, however, are clusters of deformation bands that form complex three dimensional geometries. The aim of this study is to analyze the extent and mechanisms of fluid compartmentalization due to clustered bands. Drainage multiphase fluid flow experiments were performed on a Navajo sandstone core sample characterized by diversely oriented clusters of deformation bands, that sub-divide the host rock into several compartments. Medical X-ray CT images were acquired while nitrogen was injected at progressively higher flow rates into a water-saturated core during transient and steady-state conditions. Spatial and temporal analyses of the non-wetting phase plume migration suggest that deformation bands act like capillary barriers and contribute to the development of an extremely tortuous saturation front. Differential pressure behavior across the core is linked to the breakthrough of N 2 into the individual compartments, resulting in highly variable N 2 saturation throughout the experiment. Migration into downstream compartments occurs via the exceedance of capillary entry pressure in portions of the bands. Simulation models of simplified systems demonstrate that capillary end effects and discontinuities in the deformation bands impact fluid saturation. The experiments and models presented here show that clusters of deformation bands have the potential to strongly compartmentalize a sandstone reservoir. Hence, prior analysis of the geometry of deformation band structures in a reservoir could significantly reduce the risk of overestimating reservoir capacity, and improve predictions of fluid mobility.

Quantifying occurrence of deformation bands in sandstone as a function of structural and petrophysical factors and their impact on reservoir quality: an example from outcrop analog of Productive Series (Pliocene), South Caspian Basin

“…Fossen and Bale (2007) evaluated the reduction in flow efficiency based on the differential form of steady-state Darcy equation and concluded that the permeability difference between the host rock and the deformation band should be higher than four orders of magnitude to have a significant effect on fluid flow. Romano et al (2020) and Romano et al (2021) showed via core-scale fluid flow simulations that deformation bands can act as strong capillary barriers and cause fluid compartmentalization in sandstones. Numerical simulations were also performed for carbonate (Rotevatn et al 2016) and siliciclastic (Matthai et al 1998;Sternlof et al 2006;Zuluaga et al 2016;Awdal et al 2020) reservoirs to examine the influence of deformation bands on total recovery with respect to their permeability contrast with the host rock.…”