Driving Mechanisms in CO₂-Assisted Oil Recovery from Organic-Rich Shales

Abstract

Shales are currently regarded as potential hydrocarbon resources. At the same time, utilization of carbon dioxide (CO2) in enhanced oil recovery applications is being brought to the forefront worldwide. This necessitates that the mechanisms of oil recovery using CO2 are well understood. In this study, the wettability alteration and volumetric expansion upon CO2 injection into a system comprising organic-rich shale, water, and a model oil is investigated. Captive bubble tests performed at 0.1, 10, and 15 MPa and 60 °C using different aqueous phase compositions reveal that the shale is water wet under atmospheric pressure. Additionally, it is found that CO2 has an in situ aging effect that leads to reduced surface water wetting due to the expulsion of hydrocarbons from organic matter pores. This aging effect is in direct proportion to the CO2 pressure applied. Further, at elevated pressures, divalent ions promote a reduction in water wetness, while monovalent ions have less effect. Similar to contact angle measurements, the volumetric expansion is found to increase with pressure. The solubility of CO2 in the oil phase at 10 and 15 MPa is estimated to be around 20 and 28%, respectively.

Investigation for CO2 Adsorption and Wettability of Reservoir Rocks

“…Results from our earlier studies suggest that CO 2 could drive out hydrocarbon liquids from pores of reservoir rocks, by extracting or swelling the liquids. 2,19,22,36 The extracting and swelling are due to interactions between CO 2 and the liquids and are not dependent upon specific rocks. In the present study, we focus on the potential for CO 2 to displace reservoir water from rock.…”

Experimental determination of wetting behavior under non-atmospheric conditions relevant to reservoirs: a practical guide

“…A model oil composed of 45 wt% C 16 , 45 wt% C 20 and 10 wt% C 24 was synthesized based on gas chromatography analysis of oil extracted from the shale using supercritical carbon dioxide as described in [37]. The complete analysis of the extracted oil can be found in [17]. West Texas sour crude oil was also used.…”

“…Contact angle measurements are usually studied at reservoir conditions, where brine salinity, oil composition, rock mineralogy as well as pressure and temperature are the most investigated parameters [16][17][18][19][20][21]. While the aforementioned indeed influence the wettability, there exist other factors that impact the measurements and their interpretation from a methodological perspective.…”

Heating-Assisted CO2 Huff-n-Puff for Improved CO2 Utilization: Further Discussion of the EOR Mechanism and Enhancing Carbon Sequestration in Shale Reservoirs

“…The increase in pressure will further improve the solubility of CO 2 in the oil phase and clarify the mechanism of CO 2 -assisted shale oil recovery. 16 To further explore the potential mechanism of oil recovery, there are also some studies on reservoir conditions and fluid physical properties. Goodman et al have studied the reactivity of CO 2 with Utica shales and how it impacts permeability.…”