Swelling of Coals by Supercritical Gases and Its Relationship to Sorption

Abstract

If CO 2 can be sequestered in coal seams while simultaneously displacing coalbed methane [enhanced coalbed methane (ECBM)], some of the sequestration costs can be recovered through the production of methane. One potential difficulty with ECBM is that CO 2 is known to swell coal, which may reduce its permeability. Coals also swell in other gases, although not to the same extent. Here, we report on the swelling of sub-bituminous and bituminous coals in CO 2 , CH 4 , N 2 , CF 4 , ethane, and various noble gases. Helium and Ne induced negligible swelling; all other gases swelled the coals to varying degrees. The maximum swelling was proportional to the critical temperature of the gas, except for CF 4 , which is attributed to its greater size, preventing it from penetrating the coal as completely as the other gases. This indicates that swelling of these coals by all of these gases has a similar basic mechanism; CO 2 is only different in the extent to which it swells coal. All coals swelled more in the direction perpendicular to the bedding plane than parallel to it, with the ratio of the swelling in each direction independent of pressure or gas type. Gas sorption and swelling in coal were found to be related according to a simple quadratic polynomial expression. The same relationship held for all of the coals and all gases investigated here. This means that swelling can be accurately predicted from the condensed volume of the gas adsorbed, regardless of the type of coal or gas.

Adsorptive-mechanical properties of reconstituted granular coal: Experimental characterization and poromechanical modeling

“…Understanding of the anisotropy of hydro-mechanical properties in coal seams has also been deemed of great importance (Day et al, 2010;Pan and Connell, 2012;Espinoza et al, 2013). Reconstituted coal cannot measure natural coal anisotropy because grains are randomly oriented with respect to their original configuration in the basin.…”

Swelling Measurements of a Low Rank Coal in Supercritical CO<sub>2</sub>

“…Meanwhile, some authors [5,7,11,19] concluded that swelling decreased with increasing coal rank. Figure 7 shows the maximum coal swelling (ɛ max ) as a function of coal rank from our results and those reported [6,7,[11][12][13]21,22]. There is a dependence between coal rank and swelling; higher swelling corresponds to lower coal rank.…”

“…Figure 8 shows D value as a function of coal rank based on current experiments and reported data [6,7,[11][12][13]21,22], which indicates that D value does not have a strong dependence on coal rank. Thus, because CO 2 swelling induced by CO 2 adsorption correlates strongly with the amount of CO 2 adsorbed, care should be taken when considering the factor(s) causing coal swelling.…”

Swelling and acoustic emission behaviour of unconfined and confined coal during sorption of CO2

“…Much effort has been put into studying a number of issues related to CO 2 sequestration and enhanced coalbed methane production from unminable coal seams (Bae and Bhatia, 2006;Busch et al, 2003Busch et al, , 2006Bustin et al, 2008;Ceglarska-Stefańska and Czapliński, 1993;Cui et al, 2007;Day et al, 2008Day et al, , 2010Day et al, , 2011Day et al, , 2012Fitzgerald et al, 2005;Goodman et al, 2006;Harpalani and Chen, 1995;Karacan, 2003Karacan, , 2007Keleman and Kwiatek, 2009;Larsen, 2004;Larsen et al, 1997;Majewska et al, , 2009Majewska et al, , 2010Mazumder et al, 2006a,b;Ozdemir et al, 2004;Pan et al, 2010;Pone et al, 2009a,b;Reucroft and Patel, 1986;Reucroft and Sethurman, 1987;Robertson, 2005;St. George and Bakarat, 2001;Zarębska and Ceglarska-Stefańska, 2008).…”

“…Day et al, 2008Day et al, , 2010Day et al, , 2011Day et al, , 2012Durucan and Shi, 2009;Majewska and Ziętek, 2007;van Bergen et al, 2009). However, so far, there have been only a limited number of experimental studies on the sorption of gas by constrained coal (Czapliński et al, 1986;Hol et al, 2011;Jikich et al, 2009;Pone et al, 2009a,b;Ranjith et al, 2010;Wang et al, 2010Wang et al, , 2011.…”