Evaluating the integrity of clayey sandstone rocks flooded with high pH EDTA chelating agent solutions

Abstract

Abstract Understanding the interactions between the injected enhanced oil recovery (EOR) fluids and sandstone reservoir rock minerals during the flooding processes requires special attention due to the presence of several types of highly reactive clays and non-clay minerals with different concentrations which interact with the injected non-native solutions and affect the effeciency of the oil recovery process. In this study, four coreflood experiments were carried out using two different sandstone core samples namely Gray Berea and Gray Bandera sandstone having clay contents of 8 wt% and 12 wt%, respectively, to evaluate the integrity of the clayey sandstone rocks flooded with 5 wt% and 10 wt% EDTA solutions with pH of 12. To study the presence and distribution of the clay and non-clay minerals into these sandstone rocks, x-ray diffraction (XRD), scanning electron microscope (SEM), and nuclear magnetic resonance (NMR) were used to characterize the core samples before the coreflooding tests. After the coreflooding experiments, XRD analysis was used to identify the precipitated minerals, and the alteration in the flooded rocks integrity was investigated through application of NMR, computed tomography (CT) scan analyses, and permeability measurements. The exchangeability of the chelated iron from the sandstone rocks to the EDTA solutions was studied by analyzing the produced effluents through inductively coupled plasma (ICP) analyses. The pressure drop observed during the coreflooding experiments revealed the compatibility of the injected solutions and the core samples. The results of this study dominates that Gray Berea sandstone is compatible with the 5 wt% and 10 wt% of the EDTA solutions as confirmed by the permeability measurements, CT scan analysis, NMR results, and the pressure drop during the flooding tests; which indicates that there was no fine migration, clay minerals swelling, and/or non-clay minerals dissolution caused by the interaction of Gray Berea with the EDTA solutions. On the other hand, Gray Bandera core samples were found to exhibit incompatibility with a solution of more than 5 wt% of EDTA as indicated by the CT scan and the high permeability enhancement because of the interaction of EDTA with ankerite mineral.