Viscous and Gravitational Fingering in Multiphase Compositional and Compressible Flow

TL;DR

This paper investigates viscous and gravitational fingering in complex multiphase compositional flow within porous media, revealing distinct behaviors from simpler models and highlighting the challenges in upscaling such phenomena.

Contribution

It provides a comprehensive analysis of fingering in multiphase compositional flow, considering multiple physical effects and demonstrating the limitations of existing upscaling methods.

Findings

Fingering behavior differs significantly from miscible flow cases.

Various factors like diffusion, dispersion, and heterogeneities influence instability development.

Upscaling techniques for miscible flow are not directly applicable to multiphase compositional flow.

Abstract

Viscous and gravitational fingering refer to flow instabilities in porous media that are triggered by adverse mobility or density ratios, respectively. These instabilities have been studied extensively in the past for 1) single-phase flow (e.g., contaminant transport in groundwater, first-contact-miscible displacement of oil by gas in hydrocarbon production), and 2) multi-phase immiscible and incompressible flow (e.g., water-alternating-gas (WAG) injection in oil reservoirs). Fingering in multiphase compositional and compressible flow has received much less attention, perhaps due to its high computational complexity. However, many important subsurface processes involve multiple phases that exchange species. Examples are carbon sequestration in saline aquifers and enhanced oil recovery (EOR) by gas or WAG injection below the minimum miscibility pressure. In multiphase flow, relative permeabilities affect the mobility contrast for a given viscosity ratio. Phase behavior can also change local fluid properties, which can either enhance or mitigate viscous and gravitational instabilities. This work presents a detailed study of fingering behavior in compositional multiphase flow in two and three dimensions and considers the effects of 1) Fickian diffusion, 2) mechanical dispersion, 3) flow rates, 4) domain size and geometry, 5) formation heterogeneities, 6) gravity, and 7) relative permeabilities. Results show that fingering in compositional multiphase flow is profoundly different from miscible conditions and upscaling techniques used for the latter case are unlikely to be generalizable to the former.