Regional Assessment of CO 2 -Solubility Trapping Potential: A Case Study of the Coastal and Offshore Texas Miocene Interval Changbing Yang,* Ramó n H. Treviñ o, Tongwei Zhang, Katherine D. Romanak, Kerstan Wallace, Jiemin Lu, Patrick J. Mickler, and Susan D. Hovorka Bureau of Economic Geology, The University of Texas at Austin, 10100 Burnet Road, Austin, Texas 78758, United States * S Supporting Information ABSTRACT: This study presents a regional assessment of CO 2 -solubility trapping potential (CSTP) in the Texas coastal and offshore Miocene interval, comprising lower, middle, and upper Miocene sandstone. Duan’s solubility model [Duan et al. Mar. Chem. 2006, 98, 131-139] was applied to estimate carbon content in brine saturated with CO 2 at reservoir conditions. Three approaches (simple, coarse, and fine) were used to calculate the CSTP. The estimate of CSTP in the study area varies from 30 Gt to 167 Gt. Sensitivity analysis indicated that the CSTP in the study area is most sensitive to storage efficiency, porosity, and thickness and is least sensitive to background carbon content in brine. Comparison of CSTP in our study area with CSTP values for seven other saline aquifers reported in the literature showed that the theoretical estimate of CO 2 -solubility trapping potential (TECSTP) has a linear relationship with brine volume, regardless of brine salinity, temperature, and pressure. Although more validation is needed, this linear relationship may provide a quick estimate of CSTP in a saline aquifer. Results of laboratory experiments of brine-rock-CO 2 interactions and the geochemical model suggest that, in the study area, enhancement of CSTP caused by interactions between brine and rocks is minor and the storage capacity of mineral trapping owing to mineral precipitation is relatively trivial. ■ INTRODUCTION Carbon capture and storage (CCS) has been proposed as a viable technology to reduce the emission of greenhouse gases generated through combustion of fossil fuels. 1-7 Although various deep geological media, such as depleted oil/gas reservoirs and unmineable coal seams, have been identified as possible geological storage targets, deep saline aquifers are of particular interest because of their wide distribution and huge storage potential. 4,8 A saline aquifer for CO 2 storage is generally specified as a porous and permeable body of rock capped by one or more regionally extensive, low-permeability rock formations (seals). 9 Storage of CO 2 in saline aquifers is optimal below 800 m, depths at which pressure and temperature maintain the CO 2 in a high-density fluid or supercritical state. 2 The long-term safety and performance of geological storage relies on various physical and chemical trapping mechanisms by which CO 2 is sequestered. Physical trapping of CO 2 occurs at a relatively early stage during and after CO 2 injection, when CO 2 is immobilized as a free gas or, preferably, a supercritical fluid. 10 Chemical trapping occurs at a later stage, when CO 2 dissolves into brine (solubility trapping), interacts with sedimentary rocks, and potentially is absorbed onto mineral surfaces. 1,3,10 Because of the complexity of trapping mechanisms, which can occur spatially and temporally interdependently, assessment of CO 2 -storage potential (or capacity) in a saline aquifer is particularly difficult. Published estimates of CO 2 -storage potential in deep saline aquifers focus mainly on physical trapping mechanisms. 2,8,10,11 Much less attention has been given to regional assessment of CO 2 -solubility trapping potential (CSTP), although some limited studies, such as those of the Viking aquifer 12 and Winnipegosis aquifer 13 in the western Canada sedimentary basin, the Utsira Formation at Sleipner, 14 the Oriskany Formation, 15 and the Lower Yancheng and Upper Sanduo Formations in the Subei basin, East China, 16 have been published. In these studies, CSTP values in deep saline aquifers were assessed using a volumetric method, assuming that brine in the pore space can be completely accessed by the injected CO 2 . We also used the volumetric method in this study to assess regional CSTP in the coastal and offshore Texas Miocene interval, one of the largest saline aquifers for CO 2 storage in the United States. As a potential saline CO 2 storage site, the Miocene interval has various advantages, including (1) high porosity and permeability in the sandstones; (2) thick regional shale intervals that provide potential seals; and (3) numerous depleted oil and gas fields Received: May 1, 2014 Revised: June 23, 2014 Accepted: June 24, 2014 Published: June 24, 2014 Article pubs.acs.org/est © 2014 American Chemical Society 8275 dx.doi.org/10.1021/es502152y | Environ. Sci. Technol. 2014, 48, 8275-8282