Deepwater Horizon, high-volume, low-pressure

I’ve been wrestling with the concepts involved in controlling the disaster in our Gulf of Mexico. Day after day, the spread of oil continues and we watch it grow, unable to believe that it’s actually happening, and apparently unable to do anything about it.

Deepwater-scope

Forces & Conditions

I watched the TEDxOilSpill live-stream yesterday. One of the speakers was Dr Carl Safina, President of the Blue Ocean Institute who had visited the spill site and adjacent estuaries. He spoke of a dolphin surfacing next to his boat, with expelled breath smelling strongly of oil. Motoring some distance away, the same dolphin surfaced alongside his boat once again, as though pleading for help. At that point the speaker’s voice cracked, and he took a few moments to compose himself, . . . As did I.

I’ve sailed the gulf for years, enjoying both it’s challenges and it’s beauty. Two years ago, during a midnight watch on a race from Clearwater to Key West, a pod of dolphins were attracted by illumination on our sails and rig as we made our silent passage across the top of their world. At least 5 adults and several smaller and obviously immature bottlenose dolphins paced us for hours as they played tag, keeping us company, blowing to the surface every few minutes to roll an eye and wave at us.  I’m saddened to think that one of those dolphins may have been the one that Dr. Safina spoke of.

Last week, viewing NBC’s first video of the methane burn-off at the spill site, I was shocked to witness the magnitude of the forces involved. At that point, I began to understand how large some of the issues are. The current cap effort is centered around controlling the flow at the well-head above the BOP. Maybe there’s another way that focuses on capture rather than control. I was triggered by Scott Henderson’s comments and ideas posted to Core77 where he proposed a softer solution.

DeepWater Schematic sketch

Deepwater schematic sketch

Scott’s drinking straw concept is feasible were only light-sweet crude involved. Rather than try to cap the well, which is an exercise in hydraulic engineering involving mechanical coupling with the top of the BOP, Scott’s idea, is a ‘softer’ approach. Containment, rather than a direct coupling. The containment tube enables the oil to elevator itself up to the surface, especially if the tube is vented to enable gulf-waters at the 5,000 foot depth to enter freely and support an upward flow, . . . remember, oil is lighter than water, and will lift itself due its buoyancy within what is in essence a drinking straw.

We face four primary issues in containing the oil;
1. High pressure of 13,000 psi at the BOP,
2. A steady flow of up to 2.5 million gallons a day, and,
3. A combination of oil and methane gas within that flow.
4. Methane tends to form hydrate slush at reduced temperatures and high pressures.
1. The high pressure exists only within the well-head, BOP and 21” diameter riser. Pressure becomes flow above the riser as the oil reaches equilibrium with the surrounding seawater. Pressure can be removed from the equation.

Deepwater Dome- V2.0

Deepwater Dome v2.0

2. Let’s build a bit larger riser to contain the flow rate of 100,000 gallons an hour to be directed vertically to the surface. As soon as the oil leaves the riser, the pressure is neutralized and converted to flow. Thankfully, this is aided by the buoyancy of light-sweet crude weighing 54 pounds per cu-ft, much lighter than seawater at 64 pounds /cu-ft. That’s a 15% buoyancy advantage. Due to buoyancy and the pressure gradient at the bottom of the column, the oil may almost pump itself, rising higher than sea level, as the rising column of oil weighs 85% of the weight of the surrounding water. Yeah, sounds strange, but that’s how boats float, in this case, oil. The oil floats to the surface, and we only need to capture the flow at the surface at the rate of 100,000 gallons an hour and separate it, . . . that’s plumbing and Kevin Costner.

If we begin by using the already weighted Dome assembled almost two months ago, (think re-purposing!) And seal the top with a vertically mounted railway tank car with the lower cap removed and welded into the dome.

Into the upper cap of the tank car, 60′ sections of 6′ diameter pipe is butt-welded into a continuous tube. It would take less than 100 sections of 6′ diameter pipe! Assume a team of 6-welders on a floating platform at the surface welding the pipes together into a continuous string, with a crane lowering this humongous drinking straw as sections are added at the top. Progress could proceed with a completed weld every 90-minutes, and sub-sections could even be pre-welded on a staging barge as they’re shuttled out to the site. Could proceed very quickly, producing  a mile’s worth of a low-pressure solution in days to enable oil to flow up to the surface.

Deepwater buoyancy/ballast cluster

Deepwater buoyancy/ballast cluster

The weight of this long assembly would pose other issues which could be addressed by buoyancy tanks, again from tank-cars acting to provide either lift or ballast as needed. These assemblies could also mitigate any problems caused by natural frequency of the drinking straw suspended within the Gulf currents and tidal flows.

3. The methane gas mixture then poses the greatest challenge. As it bubbles upwards, it expands, seeking equilibrium in the atmosphere above. The expansion of the methane escaping 13,000 psi pressurization within the riser is almost explosive with release to 3800 psi at the seabed.

What’s been rackin’ my brain is the separation of methane and natural gas from oil, . . . The methane’s gonna boil to the surface, being almost infinitely more buoyant that either oil or seawater. As it rises within this mile-deep column of oil and seawater flowing upward at the rate of 100,000 gallons an hour, (There are about 7.48 gallons per cu. ft. to give some scale to the problem) the natural gas continues to expand in volume as it boils to the surface. Oil being as incompressible as water, is unaffected volumetrically. But, the expansion of methane becomes a large problem, and grows larger as it nears the surface. If contained, it would attempt to rise through the column of oil, expanding and eventually reversing the upward flow of oil, . . . not good. The oil industry describes this expansion as a ‘kick’, which they believe is how the whole mess started. We need to allow the pressure to boil off by separating the methane from the oil flowing to the surface.

Would it be possible to create a string of pressure-relief stations along the drinking straw to isolate natural gas from the oil, and separate the two components of the problem? Could railway tank cars be welded into the tube-string? Each tank car acting like a diverter, isolating the gas into a chamber that is vent controlled by a float valve?

Deepwater separation chamber

Deepwater separation chamber

Any gas separation system would need to accommodate variable flow rates of gas, while maintaining a relatively constant flow rate of oil. (The inertia in a mile-long column of oil 6′ in diameter rising at the rate of -whatever- just locked up my calculator!) And better to do it closer to the bottom that toward the top. And it needn’t happen all at once, we could do it at several stages as the gas boils out of solution, (think a cold beer with those little bubbles coming from the bottom of the glass!) In concept, consider a simple side-vented float valve which would not be subject to pressure fluctuations, but would respond to the buoyancy of the float relative to the height of the oil in the chamber. At those depths, any large pressure differential would lock a normal float valve closed without counterweights.

4. This rapid expansion also creates another problem; heat is exchanged for volume and the temperature drops. A third interaction takes place as methane links with the molecular lattice of seawater at 0º C to form a slush of methane hydrates. These methane clathrates clogged the dome’s riser during the initial containment efforts.

The formation of methane clathrate can be retarded by injecting benzine to reduce the temperature of phase-transition from gas and water from liquid to solid. Injection at the dome and possibly additional chambers could reduce the build up of hydrate slush. Reducing seawater intrusion into the system during the first phase of the lift would be critical to a smooth start.

To start the elevator, as it is assembled from the top down, pumping from a catchment area surrounding the open end at sea level. As the lower dome is manuvered into place, it begins to capture oil, methane gas and seawater and the buoyancy of the oil would begin to initiate the lift. At that point, pumping from the surface into waiting barges and separation processing vessels would encourage an upward flow. With sufficient flow rates, there would be little seawater intrusion and full containment. Separation of methane gas would not interrupt the buoyant flow-rate, and could be diverted for capture.

Yes, it’s big, but it’s flexible, and it’s a high-volume, low-pressure solution. And, it’s do-able. We’re going to need a lot of engineering and even more coffee.

No, this won’t make the problem go away. And, the drill-bosses and roughnecks are drilling two relief wells around the clock, but we can’t wait for another “effort”.

I can’t watch without wanting to become involved in a solution, . . . Now, thinking about skimming equipment poses a different set of challenges, . . .

Please let me know if you have any ideas. Solving this problem is going to keep us busy for years-

Thanks-
-Dale Raymond

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One Response to Deepwater Horizon, high-volume, low-pressure

  1. stors says:

    hi??

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