The diffusional transport of methane in liquid water: method and result of experimental investigation at elevated pressure

Sachs, Werner

doi:10.1016/s0920-4105(98)00048-5

Cited by 59 publications

(36 citation statements)

References 8 publications

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“…Although self-diffusion coefficients of methane gas in pure component have been estimated by NMR experiments as 43 to 75 Â 10 À9 m 2 /s at 303 and 50 Mpa to 333 K and 30 MPa (Helbaeket al, 1996), the effective diffusion of a gas which permeates a porous medium further depends on the ratio of the mean free path of the gas to the pore dimensions, the neighboring pore structure, the nature of the gasesolid interactions, and counter-diffusion in capillaries. Diffusivity of dissolved methane in water has been estimated to range from 1.84 to 2.09 Â 10 À9 m 2 /s at 15.6413 MPa in a PVT cell and gas-autoclave at 30.088 C (Sachs, 1998). In the absence of more data, we assume is this study an equal methane isothermal porosity-dependant diffusion coefficient in both the gas and dissolved phase, and no diffusion of the hydrate phase:…”

Section: Mass Balancementioning

confidence: 98%

Numerical modeling of gas hydrate emplacements in oceanic sediments

Schnürle

Liu

2011

Marine and Petroleum Geology

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a b s t r a c tWe have implemented a 2-dimensional numerical model for simulating gas hydrate and free gas accumulation in marine sediments. The starting equations are those of the conservation of the transport of momentum, energy, and mass, as well as those of the thermodynamics of methane hydrate stability and methane solubility in the pore-fluid. These constitutive equations are then integrated into a finite element in space, finite-difference in time scheme. We are then able to examine the formation and distribution of methane hydrate and free gas in a simple geologic framework, with respect to the geothermal heat flow, fluid flow, the methane in-situ production and basal flux. Three simulations are performed, leading to the build up of hydrate emplacements largely linear through time. Models act primarily as free gas accumulators and are relatively inefficient with respect to hydrate emplacements: 26e33% of formed methane are converted to hydrate. Seepage of methane across the sea-floor is negligible for fluid flow below 2. 10 À11 kg/m 2 /s. At 5.625 10 À11 kg/m 2 /s however, 9.7% of the formed methane seeps out of the model. Moreover, along strike variation arising in the 2-dimensional model are outlined. In the absence of focused flow, the thermodynamics of hydrate accumulation are primarily onedimensional. However, changes in free methane compressibility (density) and methane solubility (the intrinsic dissolved methane flux) subtlety impact on the formation of a free gas zone and the distribution of the hydrate emplacements in our 2-dimensional simulations.

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Section: Mass Balancementioning

confidence: 98%

Numerical modeling of gas hydrate emplacements in oceanic sediments

Schnürle

Liu

2011

Marine and Petroleum Geology

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“…The free-water diffusion coefficient depends most strongly on temperature [Sachs, 1998;Lu et al, 2006], and at the temperatures of interest to this study (in the range 0 -40°C) is approximately 2 Â 10 À9 ± 1 Â 10 À9 m 2 s À1 [Lu et al, 2006]. [59] The tortuosity factor is harder to quantify over the scales of methane transport in the model.…”

Section: Dispersion Parameters: D D 0 C and Amentioning

confidence: 99%

Controls on the formation and stability of gas hydrate‐related bottom‐simulating reflectors (BSRs): A case study from the west Svalbard continental slope

2008

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[1] The growth and stability of the free-gas zone (FGZ) beneath gas-hydrate related bottom-simulating seismic reflectors (BSRs) is investigated using analytical and numerical analyses to understand the factors controlling the formation and depletion of free gas. For a model based on the continental slope west of Svalbard (a continental margin of north Atlantic type), we find that the FGZ is inherently unstable under a wide range of conditions because upward flow of under-saturated liquid depletes free gas faster than it is produced by hydrate recycling. In these scenarios, the 150-m-thick FGZ that presently exists there would deplete within 10 5 -10 6 years. We suggest the FGZ is in a stable state, however, that is formed by a diffusion-dominated mechanism that produces low concentrations of gas in a FGZ of steady state thickness. Gas forms across a thick zone because the upward fluid flux is relatively low and because the gas-water solubility decreases to a minimum several hundred meters below the seabed. This newly understood solubility-curvature effect is complementary to hydrate recycling, but becomes the most important factor controlling the presence and properties of the BSR in environments where the rate of upward fluid flow and the rate of hydrate recycling are both relatively low (i.e., rifted continental margins). If the present-day FGZ is in steady state, we estimate that the upward fluid flux in the west Svalbard site must be less than 0.15 mm a À1 .Citation: Haacke, R. R., G. K. Westbrook, and M. S. Riley (2008), Controls on the formation and stability of gas hydrate-related bottom-simulating reflectors (BSRs): A case study from the west Svalbard continental slope,

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“…These studies can be classified into two categories: conventional and unconventional techniques. In conventional techniques (Schmidt 1989;Nguyen and Farouq Ali 2008), the gas absorbed in the oil is analyzed directly by measuring composition of gas and liquid, which may provide the spatial gradient of concentration. Because this method is complex and system-intrusive (because samples are taken out subsequently), it is very expensive and time-consuming; therefore, nonconventional techniques (which do not require composition measurements) are preferred.…”

Section: Introductionmentioning

confidence: 99%

Measurement of Gas Diffusivity in Heavy Oils and Bitumens by Use of Pressure-Decay Test and Establishment of Minimum Time Criteria for Experiments

Ratnakar

Dindoruk

2015

SPE Journal

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Molecular diffusion plays a very important role in various reservoir processes, especially in the oil-recovery processes where convective forces are not dominant or when direct frontal contact and mixing are not possible. For example, in heavy-oil and bitumen recovery, injected light hydrocarbons can diffuse into the oil beyond the potential fronts and/or convective zones and promote the effectiveness of the displacement process, reducing in-situ viscosities and in turn enhancing the oil recovery.Similarly, diffusive mixing can also be a dominant mechanism in the gas-redissolution process, even in lighter-hydrocarbon systems. For example, it controls how much gas will be dissolved in oil and how long it will take to dissolve, in the absence of mechanical/convective mixing, as in the case of reservoir repressurization. The extent of dissolution of a gas into oil is governed by its solubility, but the rate is controlled by both molecular diffusivity and solubility. Thus, accurate determination of these parameters is essential to design and understand displacement processes.Despite the significance of diffusion in various aspects of oil recovery, there are very few experimental studies available in the literature addressing the diffusion of gas in heavy oils. Experimental work is most commonly based on the pressure-decay concept. However, the parameter inversion in these tests relies on an error-function solution that neglects the transient processes at the gas/oil interface and assumes constant-saturation concentration. This assumption is not appropriate when decay in pressure is large because pressure in the gas cap changes continuously as gas is dissolved in the oil, and hence the gas solubility varies with time. One of the major issues related to this experimental process is that it takes a long time (order of several days to several months) to achieve steady-state (converged) solution to determine diffusivity.In this work, we have • Experimentally investigated the diffusion of methane in heavy oils as well as light oils by use of a pressure-decay test • Captured properly the variation in gas concentration in oil at the gas/oil interface with time by expressing gas solubility in terms of Henry's constant in the mathematical model • Developed the exact solution of the 1D pressure-decay (transient-diffusion) model with pressure-dependent gas/oilinterface concentration and shown that after a long time, pressure decays exponentially in time with an exponent that depends on diffusivity as well as solubility • Presented the inversion technique to determine the diffusivity and other parameters from late-transient-pressure data, and shown the convergence in their estimates • (Most importantly) developed a cutoff criterion permitting us to stop the experiments while still being able to extract the converged diffusivity values (this is important in situations when the experiment is stopped prematurely for technical or other reasons)

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The diffusional transport of methane in liquid water: method and result of experimental investigation at elevated pressure

Cited by 59 publications

References 8 publications

Numerical modeling of gas hydrate emplacements in oceanic sediments

Numerical modeling of gas hydrate emplacements in oceanic sediments

Controls on the formation and stability of gas hydrate‐related bottom‐simulating reflectors (BSRs): A case study from the west Svalbard continental slope

Measurement of Gas Diffusivity in Heavy Oils and Bitumens by Use of Pressure-Decay Test and Establishment of Minimum Time Criteria for Experiments

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