CO₂ Sorption to Subsingle Hydration Layer Montmorillonite Clay Studied by Excess Sorption and Neutron Diffraction Measurements

Abstract

Geologic storage of CO(2) requires that the caprock sealing the storage rock is highly impermeable to CO(2). Swelling clays, which are important components of caprocks, may interact with CO(2) leading to volume change and potentially impacting the seal quality. The interactions of supercritical (sc) CO(2) with Na saturated montmorillonite clay containing a subsingle layer of water in the interlayer region have been studied by sorption and neutron diffraction techniques. The excess sorption isotherms show maxima at bulk CO(2) densities of ≈ 0.15 g/cm(3), followed by an approximately linear decrease of excess sorption to zero and negative values with increasing CO(2) bulk density. Neutron diffraction experiments on the same clay sample measured interlayer spacing and composition. The results show that limited amounts of CO(2) are sorbed into the interlayer region, leading to depression of the interlayer peak intensity and an increase of the d(001) spacing by ca. 0.5 Å. The density of CO(2) in the clay pores is relatively stable over a wide range of CO(2) pressures at a given temperature, indicating the formation of a clay-CO(2) phase. At the excess sorption maximum, increasing CO(2) sorption with decreasing temperature is observed while the high-pressure sorption properties exhibit weak temperature dependence.

FT-IR study of CO2 interaction with Na+ exchanged montmorillonite

“…Further, they found that CO 2 intercalation into dehydrated smectite results in layer expansion, with d 001 value expanding from 10.0 Å to 12.3 Å for Na + -Mt clay mineral exposed to 700 Torr CO 2 at −48°C. This latter result has been demonstrated at PT conditions relevant to CCUS with direct evidence by Rother et al (2013) based on neutron diffraction analyses and by Loring et al (2012) using XRD, MAS NMR, and in situ high pressure ATR-IR on ion-exchanged versions of Mt STx-1 with less than one monolayer of hydration in the interlayer space. Rother et al (2013) used a sodium-exchanged sample (Na + -STx-1) and Loring et al (2012) used a calcium exchanged sample (Ca ++ -STx-1).…”

On sorption and swelling of CO2 in clays

“…Experimental issues can further complicate the pore storage efficiency assessment, as discussed in Siemons and Busch (2007) or Busch and Gensterblum (2011). Rother et al (2013a) explicitly addressed the density of the sorbed phase. They report a combined excess sorption and neutron scattering study on Texas montmorillonite (STx-1) to investigate sorption amounts, interlayer swelling and sorbed phase density at temperatures of 35 and 50°C and pressures up to 15 MPa.…”

“…Busch et al 2012;Rother et al 2013a) using manometric and gravimetric sorption devices, and neutron diffraction techniques, that the excess sorption capacity can become negative at pressures exceeding *10 MPa. This means that the sorbed layer has an average density smaller than bulk CO 2 , and therefore the same amount of fluid in the sorbed layer will occupy a larger volume as compared to the bulk.…”

“…In the last 5-10 years, a series of studies (Busch et al 2008;Loring et al 2011;Rother et al 2013a;Schaef et al 2012;Weniger et al 2010, amongst others) reported on this interaction, with a major focus on swelling clays, such as montmorillonite (MMT). It was found that for CO 2 storage containment, non-negligible physical effects result from reacting clays with CO 2 at hydrostatic pressure, temperature, and stress conditions representative of geological reservoirs.…”

“…For all these measurements two different clays were used: Wyoming and Texas MMT, provided by the Clay Mineral Society and either used as provided or purified and cation exchanged. Data from de Jong et al(2014),Giesting et al (2012a, b),Rother et al (2013a),…”