Enhanced gas recovery by CO2 injection: Influence of monovalent and divalent brines and their concentrations on CO2 dispersion in porous media

Abstract

This study aims to experimentally investigate the roles of different brine types and concentrations on the longitudinal dispersion coefficient (KL) during enhanced gas recovery by CO2 injection. Core flooding process was used to simulate the displacement of CH4 by supercritical CO2 in a Buff Berea core sample at a pressure and temperature of 1400 psig and 50 o C respectively, and a CO2 injection rate of 0.3 ml/min. Individual NaCl, KCl, CaCl2 and MgCl2 solutions were prepared as test brines with ionic strengths (IS) of 1M, 2M, and 3M. The results revealed that, at lower IS of 1M, MgCl2 and CaCl2 brines had the lowest KL while the monovalent brines showed relatively higher KL. Divalent brines showed a higher degree of salting out effects at higher concentrations resulting in higher KL. The salting and drying out effects of divalent brines were responsible for higher CH4 recovery at 2M IS as CH4 comes out of solution. A hyperbolic-type relationship exists between the two properties (KL and IS), where KL decreases from 0 to 1M IS, and then increases sharply at IS >1Mthis behaviour is most pronounced in the divalent brines. Lowest contamination of the recovered CH4 was found to be between formation water salinities of 5-15 wt.%, regardless of salt type, during EGR by CO2 injection and sequestration. This study will not only present new knowledge on EGR process but will also provide an avenue for establishing a screening criterion based on formation water salinity for effective EGR process. This is a first experimental investigation which establishes the relationship between salt types and concentration and the KL in porous media.

Experimental Study on the Interplay between Different Brine Types/Concentrations and CO2 Injectivity for Effective CO2 Storage in Deep Saline Aquifers

“…Since KCl brine has the highest fluctuation of differential pressure and early breakthrough, the storability of CO 2 in this brine is the lowest as compared to other brine concentrations, which is largely because of the amount of water displaced in relation to other scenarios. This is similar to the findings of Abba [71], where KCl exhibited the highest dp trend after CO 2 breakthrough. The solubility of CO 2 in the brine solution of NaCl is slightly lower than that in the CaCl 2 brine, and both are considerably lower than that in KCl and MgCl 2 brines.…”

Carbon Capture and Storage in Depleted Oil and Gas Reservoirs: The Viewpoint of Wellbore Injectivity

“…Global warming is one of the main concerns of human beings currently and the global average temperature and sea level will reach 3.5 • C and 95 cm, respectively, by 2100 if the anthropogenic greenhouse gas (GHG) emissions continue to increase [1][2][3][4][5][6][7]. CO 2 accounts for ~64-76% of the total global GHG emissions and is one of the pollutants that endanger public health and welfare [6][7][8][9][10][11].…”

“…Several strategies have been introduced to reduce the carbon footprint, including shifting the energy mix to less carbon-intensive sources, reducing energy consumption, replacing fossil fuels with fuels that have shorter carbon chains, improving energy efficiency, and long-term carbon capture and sequestration in underground structures [5,6,12,13]. Among these, carbon capture and storage (CCS) has garnered attention because it decelerates the rate of the increase in atmospheric CO 2 concentrations [5,7,12,[14][15][16][17][18][19][20][21][22][23].…”

“…Deep saline aquifers, depleted hydrocarbon reservoirs, and hydrocarbon reservoirs of enhanced oil recovery (EOR) and enhanced gas recovery (EGR) projects, unmineable coal seams of enhanced coal bed methane (ECBM) projects, and salt domes/mined caverns are primary mediums of CO 2 sequestration [3,[6][7][8]12,13,18,22,[24][25][26][27][28][29][30][31][32][33][34]. CO 2 is trapped in these storage mediums via (i) structural trapping, where an impermeable caprock stops the CO 2 plume; (ii) capillary trapping, where CO 2 remains in pore spaces as residual CO 2 gas saturation; (iii) solubility trapping, where CO 2 dissolution produces dense CO 2 -saturated brine; and (iv) mineral trapping caused by the reaction of minerals with CO 2 -saturated brine [8,27,[35][36][37].…”

“…CO 2 sequestration in these reservoirs can provide an economic incentive, which is additional revenue from oil and gas recovered from CO 2 injection with EOR/EGR technology [7,[51][52][53][54][55]. Technologies for CCS can increase the oil recovery through EOR/EGR up to 40%, whereas a recovery factor of 1-18% can be obtained after CO 2 injection in gas reservoirs [6,7,28,48,56]. A study using a Silurian core drilled from Door District in northeast Wisconsin, United States revealed an oil recovery of 34% during CO 2 flooding [57].…”