Evolution of gas saturation and relative permeability during gas production from hydrate‐bearing sediments: Gas invasion vs. gas nucleation

Abstract

Capillarity and both gas and water permeabilities change as a function of gas saturation.Typical trends established in the discipline of unsaturated soil behavior are used when simulating gas production from hydrate-bearing sediments. However, the evolution of gas saturation and water drainage in gas invasion (i.e., classical soil behavior) and gas nucleation (i.e., gas production) is inherently different: micromodel experimental results show that gas invasion forms a continuous flow path while gas nucleation forms isolated gas clusters. Complementary simulations conducted using tube networks explore the implications of the two different desaturation processes. In spite of their distinct morphological differences in fluid displacement, numerical results show that the computed capillarity-saturation curves are very similar in gas invasion and nucleation (the gas-water interface confronts similar pore throat size distribution in both cases); the relative water permeability trends are similar (the mean free path for water flow is not affected by the topology of the gas phase); and the relative gas permeability is slightly lower in nucleation (delayed percolation of initially isolated gas-filled pores that do not contribute to gas conductivity). Models developed for unsaturated sediments can be used for reservoir simulation in the context of gas production from hydratebearing sediments, with minor adjustments to accommodate a lower gas invasion pressure P o and a higher gas percolation threshold.

Permeability of sediment cores from methane hydrate deposit in the Eastern Nankai Trough

“…In order to characterize methane hydrate-bearing sediment, proton nuclear magnetic resonance (NMR) is applied to measure pore size distribution of unconsolidated sediment (e.g., Minagawa et al, 2008). Modeling has also been attempted to understand microscale flow mechanisms by accounting for gas invasion and gas nucleation processes (Jang and Santamarina, 2014) and hydrate pore-scale growth habit and meso-scale heterogeneity (Dai and Seol, 2014). Although cores with synthetic hydrate are widely used for permeability measurements, it is important to study naturally occurring hydrate-bearing sediment in actual reservoirs to ensure accurate evaluation of gas productivity.…”

Gas production and transport during bench-scale electrical resistance heating of water and trichloroethene

“…Internal drainage has been discussed in the context of solution gas drive, carbon dioxide sequestration and geothermal reservoir applications. It can result in different distributions of gas, and different constitutive relationships, than during external drainage due to gas which nucleates and becomes trapped in pores that are not part of the most conductive channel network (Counsil and Ramey, 1979;Egermann and Vizika, 2001;Jang and Santamarina, 2014;Kamath and Boyer, 1995;Poulsen et al, 2001;Sheng et al, 1999;Zuo et al, 2012).…”

State-of-the-Art of Gas Hydrates and Relative Permeability of Hydrate Bearing Sediments

“…This mechanism can be quantified by employing the term 'permeability', which governs the gas production potential from any hydrate bearing zone (Moridis and Collett 2003;Kleinberg 2009;Pohlman et al 2009). Here, it should also be considered that the absolute permeability of one fluid will be affected by the presence of other fluid(s) (Kleinberg et al 2003;Phirani, Pitchumani, and Mohanty 2009;Liang et al 2010;Johnson, Patil, and Dandekar 2011), and therefore, it is essential to determine the relative permeability of the fluids (gas and water), at different 'hydrate occupancy' or 'hydrate saturation', which is defined as percentage of pore space occupied by hydrates (Minagawa et al 2008;Kumar et al 2010;Johnson, Patil, and Dandekar 2011;Jang and Santamarina 2014).…”

“…To overcome this, researchers have synthesized hydrates in the laboratory by employing different methodologies (Koh et al 2002;Spangenberg et al 2005;Spangenberg and Kulenkampff 2006;Takeya et al 2006;Rosenbaum et al 2007;Kingston, Clayton, and Priest 2008;Li et al 2008Li et al , 2012Johnson, Patil, and Dandekar 2011;Xiong 2012). Furthermore, determination of permeability, through conventional flow tests has been opined to be quite an intricate task that entails maintenance of constant thermodynamic conditions (Kumar et al 2010;Johnson, Patil, and Dandekar 2011;Jang and Santamarina 2014). Similarly, though some efforts have been made by the researchers (Phirani, Pitchumani, and Mohanty 2009;Liang et al 2010; to determine permeability of such sediments by resorting to numerical models, these involve over simplified assumptions such as (i) the absence of free gas and (ii) variable hydrate occupancy in the pores, which might not be resembling the real life conditions.…”