Two-phase immiscible displacement of water by gas accounting for fines migration: analytical model for vertical equilibrium

TL;DR

This paper presents an analytical model for water displacement by gas in layered reservoirs, incorporating fines migration effects that impact formation damage, injectivity, and storage capacity during CO2 sequestration.

Contribution

It extends classical models by including fines migration and straining, providing a more comprehensive understanding of displacement dynamics in CO2 storage.

Findings

Fines migration decreases well injectivity.

Fines migration increases reservoir sweep and storage capacity.

The model highlights the significant impact of fines on displacement efficiency.

Abstract

Fines migration during subterranean CO2 storage is considered as one of major contributors to formation damage and injectivity decline. The main formation damage mechanism by migrating fines is rock clogging by straining of particles in thin pore throats. The main mobilisation mechanism of attached natural reservoir fines is their detachment by capillary forces exerting from the advancing water-gas menisci. The mathematical model for displacement of water by injected CO2 from layer-cake reservoirs under fines mobilisation, migration and straining extends the classical vertical capillary-gravity equilibrium model, where hydrostatic pressure gradient is assumed in each phase. The analytical model generalises classical Buckley-Leverett problem, where the extended fractional flow accounts for permeability damage due to fines migration. We show the significant effect of fines migration on water displacement - while it decreases well injectivity, fines migration simultaneously increases reservoir sweep, increasing CO2 storage capacity.