Analysis of the Storage Capacity for CO2 Sequestration of a Depleted Gas Condensate Reservoir and a Saline Aquifer

Abstract

Summary Among the three types of geological CO2 sequestration (mature oil and gas fields, unminable coalbeds and deep saline formations), depleted gas condensate reservoirs are particularly interesting. First, because of the high-compressibility of gas, these reservoirs have larger storage capacity than oil reservoirs or aquifers. Second, the condensate that has dropped out from the gas phase during natural depletion will re-vaporize because of re-pressurization of the reservoir and by miscibility with the injected CO2. This condensate can be recovered from producing wells and leaves more pore volume for available storage of CO2. The objective of this study is to investigate the CO2 storage capacity in different formation types, for different levels of CO2 purity and different injection schedules. To this aim, we analyzed the injection of a CO2-based stream into a depleted gas condensate reservoir and into a saline aquifer using a compositional reservoir simulation model. The dynamics of the reservoir impose a minimum period of injection that is required in order for the storage scheme to benefit from 100% of the reservoir storage capacity. Hence, over and above a certain CO2 injection rate, it becomes meaningless to invest in bigger compressors to increase this rate to reduce the time of injection. When the CO2 stream contains impurities, such as N2 or methane, the storage capacity of the reservoir decreases proportionally to the impure stream's compressibility factor and its concentration of impurities. This finding suggests that an economic optimum between the costs of separation, compression and injection can be determined. Finally, the mass of CO2 sequestrated per pore volume in the equivalent aquifer model is approximately 13 times lower that of the depleted gas condensate reservoir model. This confirms that, because of their low overall compressibility, aquifers offer a far lower ratio of CO2 stored per pore volume than depleted gas condensate reservoirs. However, aquifers tend to have a far larger extent, which often compensates somewhat for this lower ratio and therefore provides storage for significant volumes of CO2.

Suitability of depleted gas reservoirs for geological CO2 storage: A simulation study

“…These petroleum fluid systems are generally divided into five categories: black oil, volatile oil, condensate gas, wet gas, and dry gas. Of these categories, gas reservoirs, which are classified into dry, wet, and condensate gas‐bearing formations, have gained the attention of many researchers in recent years as better places to store CO 2 due to the compressibility of gas . For instance, the Gorgon Carbon Dioxide Injection project in Australia has been initiated and is in its construction phase for the deployment of CO 2 in a gas field…”

“…There have been many studies carried out to show the potential of injecting CO 2 into dry gas and condensate gas reservoirs using numerical modeling techniques. According to these studies, the success of a CO 2 storage practice is linked to the injection strategy, reservoir characteristics, and operational parameters.…”

“…Of these categories, gas reservoirs, which are classified into dry, wet, and condensate gas-bearing formations, 2,3 have gained the attention of many researchers in recent years as better places to store CO 2 due to the compressibility of gas. 4,5 For instance, the Gorgon Carbon Dioxide Injection project in Australia has been initiated and is in its construction phase for the deployment of CO 2 in a gas field. 6 There have been many studies carried out to show the potential of injecting CO 2 into dry gas [7][8][9][10][11][12][13][14][15] and condensate gas reservoirs 4,[16][17][18][19] using numerical modeling techniques.…”

“…They suggested a scheme for the storage by selecting an optimum pressure or injection of a high volume of gas at the early stage of injection for a suitable gas recovery. Barrufet et al 4 evaluated the storage capacity of depleted condensate gas reservoirs and aquifers by considering formation types, level of CO 2 purity, and injection schedules. They concluded that CO 2 injection can provide a 100% recovery for condensate gas which makes these reservoirs a better place for storage compared to aquifers.…”

Laboratory Measurements of CO2-H2O Interfacial Tension at HP/HT Conditions: Implications for CO2 Sequestration in Deep Aquifers

“…Potential subsurface CO 2 disposal and storage candidates include depleted oil and gas reservoirs (Krumhansl, et al, 2002;Le Gallo et al, 2002;Oldenburg and Benson, 2002;House, et al 2003;Seo and Mamora, 2003;Pawar, et al 2004;Sobers et al, 2004;Barrufet et al, 2010;and Oldenburg and Doughty, 2010 ); coalbed methane and shale gas reservoirs (Plug, et al, 2008;Jikich, et al, 2009;Koperna and Riestenberg, 2009;and Schepers, et al, 2009); and deep saline or brackish aquifers (Pruess et al, 2001;Kumar et al, 2005;Ozah et al, 2005;Izgec et al, 2008;Nghiem et al, 2009;Fang et al;and Han et al, 2011).…”