Physics mechanisms of fines detachment and migration during CO2-water corefloods

TL;DR

This study investigates the mechanisms of fines detachment and migration during CO2-water corefloods, revealing how rock drying, fines movement, and salt precipitation impact permeability and injectivity in CCS operations.

Contribution

It provides new insights into the sequential regimes of fines detachment during CO2-water displacement and their effects on permeability decline in CCS.

Findings

Fines production peaks at the start of gas-water production.

Permeability increases abruptly during evaporation.

Fines detachment occurs mainly in the moving gas-water menisci regime.

Abstract

One of the key risks for a Carbon Capture Storage (CCS) is injectivity decline. Evaporation of the connate brine in near-wellbore region during CO2 injection may result in drying-up the rock yielding the mobilisation and migration of clay particles leading to decline rock permeability and consequent loss of well injectivity. Influx of the reservoir brine into the dried-up zone yields accumulation of precipitated salt and injectivity decline. This paper presents the results of eight coreflooding experiments aiming investigation of the effect of rock dry-out, fines migration, and salt precipitation during CO2 injection. Pressure drops across the cores, brine saturation and produced clay fines concentration versus Pore Volume Injected (PVI) have been measured. All lab tests exhibit the following features: intensive fines production at the very beginning of gas-water production period following reduced-rate fines production during overall evaporation period and continuous fines disappearance at the late stage; abrupt increase in gas permeability in the middle of evaporation, and non-monotonic evaporation rate and pressure drop. To explain these phenomena, we distinguished three sequential regimes of fines detachment during two-phase displacement: (i) moving gas-water menisci; (ii) pendular rings of residual water; (iii) dry flux, and found that for the conditions of our corefloods, detachment is possible in regime (i) only. Fines production during overall evaporation period is explained by simultaneous occurrence of three regimes during unstable displacement of water by gas in micro-heterogeneous rock.