Carbon Sequestration with Enhanced Gas Recovery: Identifying Candidate Sites for Pilot Study

Depleted natural gas reservoirs are promising targets for carbon dioxide sequestration. Although depleted, these reservoirs are not devoid of methane, and carbon dioxide injection may allow enhanced production of methane by reservoir repressurization or pressure maintenance. Based on the favorable results of numerous simulation studies, we propose a field test of the Carbon Sequestration with Enhanced Gas Recovery (CSEGR) process. The objective of the field test is to evaluate the feasibility of CSEGR in terms of reservoir processes such as injectivity, repressurization, flow and transport of carbon dioxide, and enhanced production of methane. The main criteria for the field site include small reservoir volume and high permeability so that increases in pressure and enhanced recovery will occur over a reasonably short time period. The Rio Vista Gas Field in the delta of California’s Central Valley offers potential as a test site, although we are currently looking broadly for other potential sites of opportunity. Introduction With their proven records of gas recovery, demonstrated integrity against gas leakage, existing infrastructure of wells and pipelines, and land use history of gas production and transportation, depleted natural gas fields are attractive targets for carbon sequestration by direct carbon dioxide (CO2) injection. The International Energy Agency (IEA) estimates that as much as 140 GtC could be sequestered in depleted natural gas reservoirs worldwide (IEA, 1997) and 10 to 25 GtC in the U.S. alone (Reichle et al., 1999). Although target gas reservoirs for carbon sequestration are depleted in methane (CH4) with pressures as low as 20–50 bars, they are not devoid of methane. Prior studies have suggested that additional methane can be recovered from depleted natural gas reservoirs by CO2 injection (van der Burgt et al., 1992; Blok et al., 1997; Oldenburg et al., 2001). The idea is to inject CO2 at some distance from producing wells and take advantage of the repressurization of the reservoir to produce additional CH4. The augmented methane production can be used to offset the cost of CO2 injection. We have termed this process CSEGR, or Carbon Sequestration with Enhanced Gas Recovery. Although simulations of CO2 injection into depleted natural gas reservoirs have been carried out (e.g., van der Burgt et al., 1992; Oldenburg et al., 2001), field testing of CSEGR