The Effect of Reservoir Heterogeneity on Gas Production From Hydrate Accumulations in the Permafrost

Abstract

The quantity of hydrocarbon gases trapped in natural hydrate accumulations is enormous, leading to significant interest in the evaluation of their potential as an energy source. Large volumes of gas can be readily produced at high rates for long times from methane hydrate accumulations in the permafrost by means of depressurization-induced dissociation combined with conventional technologies and horizontal or vertical well configurations. Initial studies on the possibility of natural gas production from permafrost hydrates assumed homogeneity in intrinsic reservoir properties and in the initial condition of the hydrate-bearing layers (either due to the coarseness of the model or due to simplifications in the definition of the system). These results showed great promise for gas recovery from Class 1, 2, and 3 systems in the permafrost. This work examines the consequences of inevitable heterogeneity in intrinsic properties, such as in the porosity of the hydrate-bearing formation, or heterogeneity in the initial state of hydrate saturation. Heterogeneous configurations are generated through multiple methods: 1) through defining heterogeneous layers via existing well-log data, 2) through randomized initialization of reservoir properties and initial conditions, and 3) through the use of geostatistical methods to create heterogeneous fields that extrapolate from the limited data available from cores and well-log data. These extrapolations use available information and established geophysical methods to capture a range of deposit properties and hydrate configurations. The results show that some forms of heterogeneity, such as horizontal stratification, can assist in production of hydrate-derived gas. However, more heterogeneous structures can lead to complex physical behavior within the deposit and near the wellbore that may obstruct the flow of fluids to the well, necessitating revised production strategies. The need for fine discretization is crucial in all cases to capture dynamic behavior during production.

The effect of hydrate saturation on water retention curves in hydrate‐bearing sediments

“…The m values used for gas hydrate numerical simulation studies in the literature range from m = 0.45 to m = 0.77 for hydrate saturation S h = 0.1-0.7, and the gas entry pressure ranges from 2 kPa to 100 kPa [Gamwo and Liu, 2010;Moridis and Sloan, 2007;Moridis and Reagan, 2007;Reagan and Moridis, 2008;Reagan et al, 2010;Rutqvist and Moridis, 2007]. The detailed summary about various fitting parameters is available in Jang and Santamarina [2014].…”

“…Several analytical models have been proposed to describe the water retention curve [ Brooks and Corey , ; Corey , ; Fredlund and Xing , ; van Genuchten , ]. Among them, the van Genuchten [] model is widely used for various sediment types in many other gas hydrate simulation studies [ Anderson et al ., ; Gamwo and Liu , ; Moridis and Sloan , ; Moridis and Reagan , ; Reagan and Moridis , ; Reagan et al ., ; Rutqvist and Moridis , ; Wilder et al ., ]: where P c is the capillary pressure, S w is the water saturation, S rw is the residual water saturation, P 0 is the gas entry pressure, and m is the fitting parameter. A lower m value results in steeper P c ‐ S w curve, typically in sediments with wide pore size distribution.…”

Numerical simulations of depressurization‐induced gas production from hydrate reservoirs at site GMGS3‐W19 with different free gas saturations in the northern South China Sea

“…Clarifying the relationship between gas production and secondary hydrate formation can optimize sustainable gas production strategies. 76 At present, secondary hydrate formation is generally qualitatively identified by the spatial distribution of hydrate saturation. 71 Few…”

The water retention curve and relative permeability for gas production from hydrate‐bearing sediments: pore‐network model simulation

“…Analytical expressions usually capture the water retention curve using P c , S w , and residual water saturation S rw [Brooks and Corey, 1964;Corey, 1954;Fredlund and Xing, 1994;van Genuchten, 1980]. Most numerical studies on gas hydrates [Anderson et al, 2011;Gamwo and Liu, 2010;Pooladi-Darvish, 2003, 2005;Moridis and Reagan, 2007;Moridis and Sloan, 2007;Reagan and Moridis, 2008;Reagan et al, 2010;Rutqvist and Moridis, 2007] use the van Genuchten [1980] model:…”