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Process Equipment Building |
Inside of Process Equipment Building |
Due to terrain configuration, many pipelines have low spots where significant amounts of water may accumulate. Low spots in jumper lines and manifolds may also be critical to restart because of the amount of water that can be found. Restart of wells usually starts with large amounts of gas produced; when the gas hits the low spots, several scenarios may occur. If the gas rate is fast enough, hydrates will form rapidly but water in the low spots may be evacuated and re-dispersed downstream of the low spot; however, if the gas rate is too slow, the water will remain in the low spot, hydrate formation will be slower but the large retention time of the water will favor plug formation
In a typical test, water and oil will be charged into the flow loop at the low spot and the fluids will be cooled statically into the hydrate region. A CNG compressor will allow circulation of natural gas through the fluids accumulated in the low spot. Hydrate formation rates and plug formation will be monitored through pressure measurements, a scanning gamma-densitometer and view ports on the uphill leg of the flow loop. Should a plug form, evaluation of the plug permeability will be possible knowing the gas flow rate through the plug and the differential pressure across the plug. Plug length will be evaluated using the scanning gamma-densitometer.
Brine, oil, solvents and additives can be charged from the equipment in the process building. Typically, oil, brine and solvents are charged into the flow loop at low pressure using gear pumps. The amount of each phase loaded in the flow loop is measured by a Micro Motion mass flow meter and recorded by the computer system. Water and additives can also be injected while the facility is pressurized at a very slow rate using a Milton-Roy high pressure piston pump. A brine preparation system is used to prepare brines from tap water prior to injection into the flow loop. Crude oil is circulated and heated prior to injection into the flow loop to insure dissolution of any precipitated material such as paraffins. The charge lines are heat-traced and insulated to prevent freezing, gelling and/or wax deposition.
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| Mixing Tanks and Injection Pumps |
Gas is introduced into the flow loop by volumetric displacement using high-pressure cylinders and a high-pressure piston pump. Two cylinders are used alternatively, one being charged from the gas supply while the second is being transferred into the flow loop. The gas is being withdrawn from a natural gas supply trailer and boosted up to 2,000 psia into the high pressure cylinders. To charge the flow loop the gas from one cylinder is being displaced by pumping Isopar oil on the other side of the piston using the high-pressure piston pump. Pressure and temperature of the gas leaving the cylinder is measured as well as the displaced volume of Isopar oil; the mass of gas introduced into the flow loop is then computed using equations of state and input compositions. The system allows use of the Peng-Robinson (PR), Redlich-Kwong (RK) or Benedict-Webb-Rubbin (BWR) equations of state in the gas mass computation. The gas addition system can be set to operate to charge a given mass of gas into the system and/or maintain a set pressure into the flow loop. For constant pressure tests, the measured amount of gas injected into the facility is a measurement of the hydrate formation.
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| Gas Addition System |
A John Crane seal oil system is used to maintain back-pressure on the multiphase pump seals as well as provide cooling and lubrication. This seal system constantly adjusts the back-pressure on the seals to track the flow loop pressure. An accumulator also keeps the pressure on the seals in case of a power failure, allowing sufficient time for the operators to depressurize the flow loop and bring the system to a safe condition.
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| John Crane Seal Oil System |
A 20-ton chiller is used to cool down the glycol that circulates in the annulus. The glycol is also used to cool down the seal oil and the video equipment. Temperature ramps can be programmed up to about 40ºF/hr. The glycol is circulated using a centrifugal pump and the glycol flow rate is measured with a magnetic flow meter. A second holding tank equipped with steam coils and another centrifugal pump is used to hold and circulate glycol at temperatures higher than 85ºF. A shell-tube steam heat exchanger is also used to heat up the glycol circulating in the annulus during the hydrate dissociation phase.
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| Chiller/Heater & Hydraulic System |
Steam is required as a heat source in this facility for the purpose of controlling flow loop temperature, especially during hydrate dissociation phase as well as provide heat tracing for the liquid charge lines and avoid plugging or freezing during winter conditions. A 450,000 Btu/hr boiler was purchased and installed in a boiler room. The boiler room also hosts a 25 HP air compressor to actuate the control valves, sump pump and gas booster.