DETERMINATION OF PHYSICAL PROPERTIES OF THREE GULF OFMEXICO HYDRATE FIELD GAS MIXTURES BY MEASURING SONICVELOCITIES AND DEW POINTS

摘要

During the last decade, an estimated 38,250 trillion cubic feet (Tcf) of natural gas hydratefields have been discovered in the Gulf of Mexico (GOM), over 12% of the total estimated300,000 Tcf of the United States hydrate resources. To prevent hydrocarbon condensation in theproduction system, the dew point and physical properties of these complex mixtures must beknown. The GTI Acoustic Resonance Spectrometer system can rapidly and accurately determinethese properties.Sonic speed, a thermodynamic property of a fluid, is directly proportional to its acousticradial resonance frequency. Since sonic speed is related to other state properties, fluid propertiescan be calculated. Acoustic radial frequency is also able to discriminate the phase changes of afluid as occurs at the dew point or bubble point when sound waves are propagated through thegas mixture.Three natural gas mixtures, representative of Mississippi Canyon, Green Canyon, andAtwater Hill gas hydrate fields in the GOM were prepared and their sonic speeds measured usingthe GTI acoustic resonance spectrometer. The test gas mixtures varied from 71 mol% and 23%ethane/propane to 88% methane and 8% ethane/propane. The measurements were carried out atpressures from 500 psia to 1000 psia and at temperatures from 0oC to 25oC. The dew points havealso been detected and measured. The acoustic speed of sound data show good agreement withcomputational methods, AGA8 and DDMIX, generally within ± 0.06-0.5%.