Methane Storage in Nanoporous Media as Observed via High-Field NMR Relaxometry

Abstract

The storage properties of methane gas in Vycor porous glass (5.7 nm) are characterized in a wide pressure range from 0.7 MPa-89.7 MPa using Nuclear Magnetic Resonance (NMR). We demonstrate the capability of high field NMR relaxometry for the determination of the methane gas storage capacity and the measurement of the Hydrogen Index, to a high degree of accuracy. This helps determine the excess gas in the pore space which can be identified to exhibit Langmuir properties in the low pressure regime of 0.7 MPa to 39.6 Mpa. The Langmuir model enables us to determine the equilibrium density of the monolayer of adsorbed gas to be 8.5% lower than that of liquid methane. We also identify the signatures of multilayer adsorption at the high pressure regime from 39.6 Mpa to 89.7 Mpa and use the Brunauer-Emmet-Teller (BET) theory to determine the number of adsorbed layers of methane gas. We show how these measurements help us differentiate the gas stored in the Vycor pore space into free and adsorbed fractions for the entire pressure range paving way for similar applications such as studying natural gas storage in gas shale rock or hydrogen storage in carbon nanotubes. arXiv:1507.06861v2 [physics.geo-ph] 3 Sep 2015

Monitoring gas hydrate formation with magnetic resonance imaging in a metallic core holder

“…The long T1 signal component, on the order of 10 seconds, was confirmed by bulk T1 measurement undertaken as outlined above. T1 lifetimes generally increase with pressure for spin ½ gases due to the spin rotation relaxation mechanism [24]. Since it is difficult to unambiguously assign peak P4 to pore gas through a control experiment we must consider alternate hypotheses.…”

“…Important evidence in support of the pore gas hypothesis is the bifurcation in the T1 and T2 relaxation times of peak P4. Pure methane gas, under the same bulk pressure and temperature conditions, has equivalent T1 and T2 as observed in peak P1 [24,25]. Methane gas at elevated pressure in microporous solids is known to bifurcate in T1 and T2 with T2 often substantially reduced from T1 [23,24].…”

Spatially-resolved 1H NMR relaxation-exchange measurements in heterogeneous media

“…Inverse Laplace Transform (ILT) by Venkataramanan, Song and Hürlimann [37] and Hürlimann and Venkataramanan [38], pseudo-3D experiments for the study of diffusive exchange, like , represent undoubtedly the most complex and detail-rich approaches [14,[39][40][41][42]. The pulse sequence consists of two CPMG loops separated by a longitudinal storage period called mixing time ( ), during which diffusive coupling and/or chemical exchange may take place [43][44][45].…”

Equation of state for methane in nanoporous material at supercritical temperature over a wide range of pressure

“…Shale, characterized by abundant nanopores, including organic kerogen pores and inorganic pores, hosts free gas and adsorbed gas because of large internal surface area 14 . In addition, these nanopores are irregular in cross section, including bubble-like, elliptical and faveolated shapes 15 .…”

“…Gas storage behavior in nanoporous materials can be investigated through experiments 5,14,[48][49][50] , molecular dynamic (MD) simulations 8,11,46,51 , mathematical models 47 , [52][53] , and combining these methods [54][55] . Experiments are the closest to reality, furthermore, with rapid advancement in experimental equipment and technology today, it is possible by direct observation to open out some undiscovered and underlying mechanisms, such as adsorption sites determination 49 , adsorbed gas molecules structures and ordering 50 .…”