Natural Gas Hydrates at Pressures to 10,000 psia

Abstract

This paper presents the results of the data obtained in the first stage of a long-range study at high pressures of the system, vapor-hydrate-water rich liquid-hydrocarbon rich liquid. The data presented are for the three-phase systems in which no hydrocarbon liquid exists. Tests were performed on 10 gases at pressures from 1,000 to 10,000 psia. One of these was substantially pure methane, and the remainder were binary mixtures of methane with ethane, propane, iso-butane and normal butane. Several conclusions may be drawn from the data.Contrary to previous extrapolations, the hydrocarbon mixtures tested form straight lines in the range of 6,000 to 10,000 psia which are parallel to the curves for pure methane, when the log of pressure is plotted vs hydrate formation temperature.The hydrate formation temperature may be predicted accurately at pressures from 6,000 to 10,000 psia by using a modified form of the Clapeyron equation. The total hydrate curve may be predicted by using the vapor-solid equilibrium constants of Carson and Katz to 4,000 psia and joining the two segments with a smooth continuous curve between 4,000 and 6,000 psia.The use of gas specific gravity as a parameter in hydrate correlations is unsatisfactory at elevated pressures.The hydrate crystal lattice is pressure sensitive at elevated pressures. Introduction Prior to 1950 many studies had been made of the hydrate forming conditions for typical natural gases to pressures of 4,000 psia. Most of these attempted to correlate the log of system pressure vs hydrate formation temperature, with gas specific gravity as a parameter. One of the more promising correlations was made by Katz, et al, which utilized vapor-solid equilibrium constants. The only published data above 4,000 psia are those of Kobayashi and Katz for pure methane to a pressure of 11,240 psia. In the intervening years, most published charts for the high-pressure range have represented nothing more than extrapolations of the low-pressure data, with the methane line serving as a general guide. The reliability of these charts has become increasingly doubtful (and critical) in our present technology as we handle more high-pressure systems.

Isothermal Phase Equilibria for Methane + Ethane + Water Ternary System Containing Gas Hydrates

“…(2), the three-phase equilibrium pressures increase monotonically as temperature increases. Under the present experimental condition, the three-phase equilibrium curves of CH 4 + C 2 H 6 mixed-gas hydrate would not intersect that of pure CH 4 hydrate, opposed to the previous data [14]. The structural transition points obtained in the present study agree with those reported by Subramanian, Kini, Dec and Sloan [1].…”

Experimental Study of Mixed Gas Hydrates from Gas Feed Containing CH4, CO2 and N2: Phase Equilibrium in the Presence of Excess Water and Gas Exchange

“…This experimental setup and procedure employed to measure phase equilibrium with the Titanium pressure cell was validated by measuring HVLE data of pure CH4 and pure H2O. A p-T dissociation point of (9.459 MPa, 285.79 K) is measured, which is in good agreement with the average value of (9.441 MPa, 285.74 K) from other experiments [50][51][52][53].…”

Enthalpy of dissociation and hydration number of methane hydrate from the Clapeyron equation

“…For most other gas hydrates, which exist at pressures much lower than that of methane hydrate, the method outlined here is also expected to work extremely well. [20] 19.06 Roberts et al [21] 54.36 Deaton and Frost [6] 55.12 McLeod and Campbell [14] 55.07 Marshall et al [10] 53.41 Yoon et al [22] 53.81 17.53 Glew [23] 55.36 18.06 Present work 52.9 ± 1.3 17.47 ± 0.10 In evaluating the fugacity it is assumed that the gas is pure methane, whose equation of state is found in the NIST webbook [9]. The methane solubility found by the procedure outlined above is given in figure 6.…”

“…The volume change for reaction (1a) is Galloway et al [12] Deaton and Frost [6] Kobayashi and Katz [13] McLeod and Campbell [14] Verma [15] de Roo et al [16] Thakore and Holder [17] Adisasmito et al [18] Makogon and Sloan [7] DV 1a ¼ 1 À…”