Investigation of Potential Geochemical Reactions in Large-Scale Carbon Dioxide - Enhanced Oil Recovery (CO2-EOR) Carbonate Reservoirs

Abstract

The Midwest Regional Carbon Sequestration Partnership (MRCSP) is responsible for the assessment of large-scale carbon dioxide (CO2) storage associated with enhanced oil recovery (EOR) operations in oilfields that have undergone primary production. As part of this overall program, Battelle has collaborated with The Ohio State University (OSU) and Lawrence Livermore National Laboratory (LLNL) to perform studies investigating potential geochemical reactions caused by the injection of CO2 and resulting changes to the hydrologic conditions (i.e., porosity and permeability) of the reservoir. Initially, geochemical equilibrium modeling was performed using analytical data from brine samples collected from the EOR reservoirs. The models indicated that the brines were supersaturated with respect to several carbonate and sulfate minerals prior to the injection of CO2. The model results also indicated that the saturation levels of these minerals increased with the injection of CO2. Following the modeling efforts, rock (core) samples collected from the reservoirs were analyzed using scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX) and powder x-ray diffraction (XRD) to investigate the elemental chemistry and mineralogy of the mineral precipitates present in the large pores and vugs of the core samples. Additionally, stable carbon isotope analyses were performed on the mineral precipitates to assess the origin of the carbon present in the carbonate minerals. High-resolution micro x-ray computed tomography (XRCT) analysis of core samples collected following the injection of CO2 was performed to investigate changes in the rock fabric, pore geometry, and fracture conditions resulting from the CO2 injection. The XRCT scans did not find evidence of mineral dissolution along the fracture surfaces, nor were significant through-going connected fluid pathways observed in any of the core sub-samples. The most compelling evidence for CO2-induced dissolution was subtle, comprised of localized areas of elevated porosity within regions displaying similar textures, or slight fracture widening in some cases. In contrast, the evidence of mineral precipitation, lining large pores and even fractures of one sample, was apparent throughout the sub-samples. MRCSP is supported by U.S. DOE-NETL Agreement No. DE-FC26-0NT42589

AAPG Datapages/Search and Discovery Article #90335 © 2018 AAPG 47th Annual AAPG-SPE Eastern Section Joint Meeting, Pittsburgh, Pennsylvania, October 7-11, 2018