The Effect of Fines Migration During CO2 Injection Using Pore Scale Characterization

Abstract

Recent laboratory studies have shown fines migration induced decrease in rock permeability during CO2 injection. Fines migration is a pore scale phenomenon, yet previous laboratory studies did not conduct comprehensive pore scale characterization. This study utilizes integrated pore scale characterization techniques to study the phenomenon. We present CO2 injection experiments performed on two Berea sandstone samples. The core samples are characterized using nitrogen permeability, X-ray micro-computed tomography (micro-CT), Scanning Electronic Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) and Itrax X-ray Fluoresence (XRF) scanning. The core samples were flooded with freshwater, then CO2-saturated water, and finally water-saturated supercritical CO2 (scCO2). To calculate permeability, the pressure difference across the core samples was monitored during these fluid injections. The produced water samples were analysed using Inductively Coupled Plasma-Optical Emission Spectrometry (ICPOES). After the flooding experiment, nitrogen permeability, micro-CT, SEM-EDS and Itrax-XRF scanning was repeated to characterize pore scale damage. Micro-CT image based computations were run to estimate permeability decrease along the core sample length after injection. Results show dissolution of dolomite and other high density minerals. Mineral dissolution dislodges fines particles which migrate during scCO2 injection. Berea 1 and Berea 2 showed respectively 29% and 13% increase in permeability during CO2-saturated water injection. But after water-saturated scCO2 injection, both Berea 1 and Berea 2 showed 60% decrease in permeability. The permeability damage of the sample can be explained by fines migration and subsequent blockage. SEM-EDS images also show some examples of pore blockage.

Effect of scCO2-brine mixture on injectivity and storage capacity in rock samples of naturally fractured carbonate formations

“…Injection of CO 2 -saturated brine results in a low pH that can cause dissolution of mineral cement and generation of particles with migration of fines (Othman et al, 2018b) Mathematically it has been shown (Huang et al, 2018) that wettability influences the interfacial forces acting on fine particles, with their subsequent associated displacement. Capillary forces or wettability can reduce injection when fine migration occurs (Guo et al, 2018;Chequer et al, 2018;Russell et al, 2018), with pore blockage during CO 2 sequestration tests (Othman et al, 2018a).…”

“…In the injection process into the reservoir, the mineral particles present can be detached, being suspended in the injected fluid and, when their size allows, strain in the pore throats during transport. This results in a significant decrease in the permeability of the porous medium due to the process known as fines migration, which can significantly influence the capacity of the injection wells by supplying fluid to the reservoir (Othman et al, 2018a;Othman et al, 2018b).…”