Fines migration during supercritical CO2 injection in sandstone

Sandstone formations are widely considered for underground sequestration of CO2. During CO2 injection, fines migration can cause pore blockage, which reduces sandstone permeability and CO2 injectivity. To better the understanding of the mechanism of fines migration during CO2 injection, this study characterizes the fines mobilized. This paper presents a CO2 injection experiment with detailed characterization of the rock and fluids produced. A Berea sandstone core sample is used. To characterize the core sample, X-Ray powder Diffraction (XRD), X-Ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM) analyses are performed. The core receives injection first of brine (10g/l NaCl), then of CO2-saturated brine, and finally of brine-saturated supercritical CO2 (scCO(2)). During the injection, pressure difference between the core's injection face and production face is recorded. Samples of produced water are used for calculating produced fines concentration and for ionic chromatography. Then fines are separated from the produced water samples for further characterization. After the experiment, SEM images of the core are taken and compared with the pre-injection images to assess fines migration. Energy Dispersive X-ray Spectroscopy (EDS) is run on the post-injection SEM images to identify the fines blocking the pores. SEM-EDS analysis of the produced fines and blocked pores in the core show that blockage is caused by clay, quartz, and cement. Ionic chromatography for produced water during CO2-saturated brine and brine-saturated scCO(2) injection show an increase in the ions present in the intergranular cement of Berea core. This indicates that CO2-saturated brine dissolved the cement, resulting in dislodgement of clay and quartz particles, some of which blocked the pore space near the core production end and thereby reduced permeability.