Supercritical CO2 and H2S—Brine Drainage and Imbibition Relative Permeability Relationships for Intergranular Sandstone and Carbonate Formations

Abstract

Abstract Sequestration of CO2 and H2S (acid gas) in deep underground formations is a means for reducing atmospheric emissions of acid gas produced from sour gas reservoirs that has been practiced for 15 years in North America and that is currently being considered in other regions such as the Middle East and central Asia. Furthermore, acid-gas injection operations constitute a commercial-scale commercial analogue to CO2 injection in geological media as a climate change mitigation measure. Deep saline aquifers provide a very large capacity for the sequestration of acid and greenhouse gases, being ubiquitous in all sedimentary basins around the world. Proper understanding of the relative permeability character of such systems is essential in ascertaining gas injectivity and migration, and in assessing the suitability, containment and safety of prospective injection sites. Pure CO2 and H2S represent the compositional end-members of acid and greenhouse gases, thus the interest in measuring their displacement properties. This paper presents the detailed experimental equipment and protocols, and the results of a series of relative permeability tests conducted at full reservoir conditions using supercritical pure CO2 and H2S on samples of intercrystaline sandstone and carbonate rocks from the Wabamun Lake area in central Alberta, Canada, where large CO2 sources and several acid-gas injection operations exist. Results for both drainage and imbibition relative permeability experiments are presented for each fluid and rock type, as well as measurements of the interfacial tension (IFT) between brines and CO2 and H2S at in situ conditions, and correlations of these results with the IFT, measured rock capillary pressure, pore size distribution and mineralogical data. The results allow a comparison between the drainage and imbibition relative permeability character and performance of the two gases, and provide a valuable dataset for the evaluation and simulation of acid gas disposal and CO2 storage projects.