Dissolved methane

The other state variables are the fugacity of dissolved methane in the bulk of the liquid water phase (fb) and the zero, first and second moment of the particle size distribution (p0, Pi, l )- The initial value for the fugacity, fb° is equal to the three phase equilibrium fugacity feq. The initial number of particles, p , or nuclei initially formed was calculated from a mass balance of the amount of gas consumed at the turbidity point. The explanation of the other variables and parameters as well as the initial conditions are described in detail in the reference. The equations are given to illustrate the nature of this parameter estimation problem with five ODEs, one kinetic parameter (K ) and only one measured state variable. 

Live oil with dissolved methane does not follow the above correlations as methane relaxes by a spin-rotation mechanism, even when dissolved in liquid hydrocarbons [13]. The Ti relaxation time as a function of rj/T is illustrated in Figure 3.6.2 for different gas/oil ratios expressed in units of m3 m-3 as a parameter. The solid line is the fit for zero gas/oil ratio and is given by Eq. (1). 

The trends shown from the predicted curves, Csh and Cs, are in qualitative agreement with corresponding dissolved methane Raman peak intensities. Therefore, the Raman spectra (Figure 3.27a) support the proposed mechanism that hydrate growth occurs in part as a result of methane diffusing from the bulk aqueous phase to the hydrate film formed at the vapor-liquid interface. This decreases the methane concentration in the bulk water phase. Hydrate growth from an aqueous... 

Figure 3.27 Methane hydrate film development at the water-methane interface from dissolved methane in the aqueous phase, as indicated from Raman spectroscopy (a) and methane solubility predictions (b). (a) A series of Raman spectra of dissolved methane collected at different temperatures during the continuous cooling process. Spectra marked A through E correspond to temperatures of 24°C, 20°C, 15.6°C, 10.2°C, and 2.8°C, respectively. (b) A schematic illustration of temperature dependencies of the equilibrium methane concentration in liquid water (C = without hydrate, Qjh = with hydrate). The scale of the vertical axis is arbitrary, but the Raman peak area is proportional to methane dissolved in water. Points A through F correspond to different temperatures during the continuous cooling process. (From Subramanian, S., Measurements ofClathrate Hydrates Containing Methane and Ethane Using Raman Spectroscopy, Ph.D. Thesis, Colorado School of Mines, Golden, CO (2000). With permission.)...

Hydrates may also exist in equilibrium with only a fluid hydrocarbon phase (either vapor or liquid) when there is no aqueous phase present. Two-phase (H-V or H-Lhc) regions are shown in the T-x diagram of Figure 4.3. Similarly, Figure 4.3 shows the Lw-H region for hydrates in equilibrium with water containing a small amount of dissolved methane, as in the case for hydrate formation in oceans, as exemplified in Chapter 7. 

A schematic process flow sheet is shown in Figure 2. Inlet gas, a mixture of methane, hydrogen and carbon monoxide at 100°F and 500 psia (stream 1) is successively cooled to -140°C by the outlet gas stream from the absorber and some recycle gas. The absorber is a packed column of 1-in. berl saddles with 50% void fraction. The rich liquid from the bottom of the absorber is heat exchanged with the bottom liquid from the stripper. The stripper is also a packed column with 1-in. berl saddles. The dissolved methane, hydrogen, and carbon monoxide is stripped out by heating at the bottom of the stripper. The outlet gas stream from the stripper is heated in a heat exchanger by a recycle gas stream and is further compressed to produce the final methane product at 100°F and 1000 psia. 

A multi-disciplined team interviewed witnesses and performed tests, and the evidence was followed to a sound conclusion. Investigators sent the explosion meters (flammable gas detectors) to the instrument shop for examination. The welding torch was also inspected. Experts found both the torch and the meter behaved satisfactorily. There was speculation that some aquatic life deteriorated and formed methane, but that was not the case. They concluded that the fuel was dissolved methane from the well water system that was routed to the pump seal. Trace amounts of dissolved methane (about 0.02 percent by volume) accumulated in the well water stream flowing through the 3/8-inch-diameter stream on the... 

Popp B. N., Sansone F. J., Rust T. M., and Merritt D. A. (1995) Determination of concentration and carbon isotopic composition of dissolved methane in sediments and nearshore waters. Anal. Chem. 67, 405-411. 

Scranton M. 1. and Brewer P. G. (1978) Consumption of dissolved methane in the deep ocean. Limnol. Oceanogr. 23, 1207-1213. 

Hanor J. S. (1980) Dissolved methane in sedimentary brines potential effect on the PVT properties of fluid inclusions. Econ. Geol. 75, 603-609. 

Kelley C. A. and Jeffrey W. H. (2002) Dissolved methane concentration profiles and air-sea fluxes from 41°S to 27°N. Global Biogeochem. Cycles 16, 10.1029/2001GB001809. 

Methane oxidation kinetics was assessed as follows. In these experiments, cells were inoculated into medium containing different initial amounts of copper sulfate and grown to an optical density at 600 nm of 0.5-0.7. Aliquots were then placed in closed vials at different initial dissolved methane concentrations. These aliquots were incubated under optimal conditions, and head-space samples were taken at four different time points (1-4 h) for determination of methane concentrations by gas chromatography. From these data, initial methane consumption rates determined for different methane concentrations were used to obtain the Michaelis-Menten parameters Ks (half-saturation constant) and Vmax (rate at substrate saturation). Under these conditions sMMO was not expressed, as described previously (9). 

Seasonal Cycles of Dissolved Methane in the Southeastern Bering Sea... 

Methane August, 1980. The surface distribution of dissolved methane (nL/L, STP) in August 1980 is shown in Figure 3a. The highest surface concentrations were found near the entrance to Port Moller and near Unimak Pass (see Figure 1). At the entrance to Port Moller, concentrations of dissolved methane were greater than 2500 nL/L (about 35 times the equilibrium value) and decreased along the coast toward the northeast. The direction of the methane plume marks the mean drift of the coastal current. 

Methane September. 1975 and July. 1976. Concentrations of dissolved methane also were measured ih the southeastern Bering Sea in the fall of 1975 and again during the following summer. These observations are shown for both surface and near-bottom waters in Figures (7a,b, and 8a,b). 

The coastal zone is somewhat anomalous. There, the depth of water is shallow (z < 50m) and the bottom sediments are coarse-grained and low in organic carbon. Because of these factors, the concentration of methane in the water column should be near its atmospheric equilibrium solubility, however the coastal waters receive large amounts of freshwater, which are rich in dissolved methane, thus raising the concentration above that expected from in situ sources along. 

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