Browsing by Subject "Gas Hydrate"
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Item Controlled-source electromagnetic modeling of the masking effect of marine gas hydrate on a deeper hydrocarbon reservoir(2009-06-02) Dickins, DavidThe ability of marine controlled-source electromagnetic (MCSEM) methods to help image electrical conductivity contrasts below the Earth?s surface makes them useful for both initial reconnaissance surveying for hydrocarbons and for delineating prospective regions of high resistivity in development drilling. A 3-D finite-element MCSEM Fortran algorithm used for forward modeling was developed by Badea. Additional code was written and used for this thesis, with the goal of enforcing more realistic electromagnetic (EM) Dirichlet boundary value conditions. The results of the new boundary conditions on a MCSEM survey model, with a hydrocarbon-saturated region in the subsurface, show that the method does not work as hoped. Constant boundary values were applied to gauge the transmitter-receiver (TXRX) range at which results are not boundary influenced, using a hydrate/hydrocarbon model of the subsurface, at each of the three transmitter frequencies used in this study (1 Hz, 3 Hz, and 10 Hz). Results showed that electric field data were reliable to roughly 5000 m of TX-RX offset for the 1 Hz and 3 Hz cases, and to 6500 m offset for 10 Hz. The gas hydrate/hydrocarbon model was then run with zero-value boundary conditions. The goal was to determine what effect changing parameters of the gas hydrate, including hydrate radius, thickness, and depth, have on the EXEXS (xcomponent of secondary electric field inline with the transmitter dipole axis) curves at various offset, particularly in relation to a hydrocarbon-only model of the subsurface response, so as to evaluate the EM masking effect the hydrate has on the hydrocarbon. The results showed that the x-component of electric field in an inline survey is dominated by the hydrate response, in all cases studied, with a couple of exceptions. One exception is 1 Hz transmitter frequency at 2500 m to 3000 m offset when depth to top of the massive gas hydrate zone was greater or equal to 250 m. Receivers at these offsets would successfully detect the hydrocarbon target.Item Prediction of gas-hydrate formation conditions in production and surface facilities(Texas A&M University, 2006-10-30) Ameripour, ShararehGas hydrates are a well-known problem in the oil and gas industry and cost millions of dollars in production and transmission pipelines. To prevent this problem, it is important to predict the temperature and pressure under which gas hydrates will form. Of the thermodynamic models in the literature, only a couple can predict the hydrate-formation temperature or pressure for complex systems including inhibitors. I developed two simple correlations for calculating the hydrate-formation pressure or temperature for single components or gas mixtures. These correlations are based on over 1,100 published data points of gas-hydrate formation temperatures and pressures with and without inhibitors. The data include samples ranging from pure-hydrate formers such as methane, ethane, propane, carbon dioxide and hydrogen sulfide to binary, ternary, and natural gas mixtures. I used the Statistical Analysis Software (SAS) to find the best correlations among variables such as specific gravity and pseudoreduced pressure and temperature of gas mixtures, vapor pressure and liquid viscosity of water, and concentrations of electrolytes and thermodynamic inhibitors. These correlations are applicable to temperatures up to 90????F and pressures up to 12,000 psi. I tested the capability of the correlations for aqueous solutions containing electrolytes such as sodium, potassium, and calcium chlorides less than 20 wt% and inhibitors such as methanol less than 20 wt%, ethylene glycol, triethylene glycol, and glycerol less than 40 wt%. The results show an average absolute percentage deviation of 15.93 in pressure and an average absolute temperature difference of 2.97????F. Portability and simplicity are other advantages of these correlations since they are applicable even with a simple calculator. The results are in excellent agreement with the experimental data in most cases and even better than the results from commercial simulators in some cases. These correlations provide guidelines to help users forecast gas-hydrate forming conditions for most systems of hydrate formers with and without inhibitors and to design remediation schemes such as: ???? Increasing the operating temperature by insulating the pipelines or applying heat. ???? Decreasing the operating pressure when possible. ???? Adding a required amount of appropriate inhibitor to reduce the hydrateformation temperature and/or increase the hydrate-formation pressure.Item Temporal changes in gas hydrate mound topography and ecology: deep-sea time-lapse camera observations(Texas A&M University, 2004-09-30) Vardaro, Michael FredricA deep-sea time-lapse camera and several temperature probes were deployed on the Gulf of Mexico continental shelf at a biological community associated with a gas hydrate outcropping to study topographic and hydrologic changes over time. The deployment site, Bush Hill (GC 185), is located at 27?47.5' N and 91?15.0' W at depths of ~540m. The digital camera recorded one still image every six hours for three months in 2001, every two hours for the month of June 2002 and every six hours for the month of July 2002. Temperature probes were in place at the site for the entire experimental period. The data recovered provide a record of processes that occur at gas hydrate mounds. Biological activity was documented by identifying the fauna observed in the time-lapse record and recording the number of individuals and species in each image. 1,381 individual organisms representing 16 species were observed. Sediment resuspension and redistribution were regular occurrences during the deployment periods. By digitally analyzing the luminosity of the water column above the mound and plotting the results over time, the turbidity at the site was quantified. A significant diurnal pattern can be seen in both luminosity and temperature records, indicating a possible tidal or inertial component to deep-sea currents in this area. Contrary to expectations, there was no major change in shape or size of the gas hydrate outcrop at this site on the time frame of this study. This indicates that this particular mound was more stable than suggested by laboratory studies and prior in situ observations. The stable topography of the gas hydrate mound combined with high bacterial activity and sediment turnover appears to focus benthic predatory activity in the mound area. The frequency and recurrence of sediment resuspension indicates that short-term change in the depth and distribution of surface sediments is a feature of the benthos at the site. Because the sediment interface is a critical environment for hydrocarbon oxidation and chemosynthesis, short-term variability and heterogeneity may be important characteristics of these settings.