Sammendrag
Hydrate conditions for several new deepwater field developments in the Gulf of Mexico are at greater severity than previous shallower water developments. The new deepwater conditions have introduced new challenges for Flow Assurance, particularly in the area of laboratory testing and qualification.
In the SINTEF hydrate laboratory, crude oil samples from a Gulf of Mexico deepwater oil field with flowing pressures in excess of 500 bar were tested under realistic flow conditions, with a candidate LDHI chemical for hydrate management. The flow loop designed for these tests is capable of 1000 bar maximum pressure, and is designed as a wheel, with 2" ID piping. The liquids see an "infinite" pipe, through which they flow without having to go through a pump. Several sets of experiments were run under two different regimes:
• medium high pressure of 210 bar, and
• high pressure of 500-530 bar.
The inhibitor, which is an anti-agglomerant low dosage hydrate inhibitor (LDHI), performed well at high pressure, but surprisingly failed to provide flow assurance at medium pressure conditions.
Probable explanations for these effects do not completely rule out procedure or system errors, but we judge that the differences are due to an actual effect of the high pressure conditions, and possible mechanisms for this are discussed in the paper. These include possible effects on polymer conformation at different pressures, influencing the diffusion efficiencies (and thereby the ability to reach surfaces), the effects on viscosity and gas dissolution at different pressure regimes, as well as the possibility that the oil emulsion characteristics may be very different at varying pressure.
Though the exact cause for the reported phenomena is not known at present, these tests provide a valuable reminder that effects of extreme conditions are often poorly represented in widely used experimental equipment, models, correlations and assumptions.
In the SINTEF hydrate laboratory, crude oil samples from a Gulf of Mexico deepwater oil field with flowing pressures in excess of 500 bar were tested under realistic flow conditions, with a candidate LDHI chemical for hydrate management. The flow loop designed for these tests is capable of 1000 bar maximum pressure, and is designed as a wheel, with 2" ID piping. The liquids see an "infinite" pipe, through which they flow without having to go through a pump. Several sets of experiments were run under two different regimes:
• medium high pressure of 210 bar, and
• high pressure of 500-530 bar.
The inhibitor, which is an anti-agglomerant low dosage hydrate inhibitor (LDHI), performed well at high pressure, but surprisingly failed to provide flow assurance at medium pressure conditions.
Probable explanations for these effects do not completely rule out procedure or system errors, but we judge that the differences are due to an actual effect of the high pressure conditions, and possible mechanisms for this are discussed in the paper. These include possible effects on polymer conformation at different pressures, influencing the diffusion efficiencies (and thereby the ability to reach surfaces), the effects on viscosity and gas dissolution at different pressure regimes, as well as the possibility that the oil emulsion characteristics may be very different at varying pressure.
Though the exact cause for the reported phenomena is not known at present, these tests provide a valuable reminder that effects of extreme conditions are often poorly represented in widely used experimental equipment, models, correlations and assumptions.