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(from the Oil Drum)
1) The BOP and riser are anchored to the earth via steel pipe that is inserted thousands of feet into the well hole. Any force resisting the flow of oil and gas must be countered by this anchor. Whether the leak is stopped in the riser or BOP, the strain would be transmitted into the wall of the well hole.
2) Oil and gas are coming out under great pressure, far more than most of us have experienced (think multiple times higher than a scuba or CO2 tank).
3) If the oil and gas could be stopped instantly, the force of the moving oil and gas would spike to extremely high levels and could potentially blow open the riser, blowout the BOP, or even fracture the rock around the well hole, thereby destroying the anchor into the earth (think a very bad water hammer in a pipe). Therefore, the flow or oil and gas must be slowed gradually.
4) The only way to slow the flow at the top of the well is to resist it, either with one or more solid objects (junk, balls, valves, etc.) and/or with opposing pressure of either a liquid or gas (gas compresses, so it won't work, so liquid it is). The liquid of choice here is drilling mud.
5) The challenge of using a liquid is that it will flow to lower pressure outlets first. Since the ocean water is at lower pressure than the oil flowing out of the well, any liquid pumped against the flowing oil will tend to flow out into the ocean through the holes in the riser rather than into the well. It's like holding two garden hoses against each other so that the force of one balances the force of the other, the problem being that the water will tend to squirt out into the air through the gap between the hoses. In theory, if the pressure and flow were high enough and the outlets to the ocean are small enough, the leaks into the ocean would be too small to matter and mud pressure could be gradually increased to a point where the oil and gas would stop flowing.
6) One problem with using a moving liquid is that the pressure of any liquid here is so high that it erodes steel as it blasts past the steel. This is likely why the holes in the riser are getting worse; the mud and oil are literally cutting away the steel in the riser pipe. The question becomes, is the pressure in the drilling mud high enough to force back the oil while it also jets out through the holes in the riser given the size of the holes? Also, as mud pressure increases, will the mud and oil cut the holes in the riser faster than pressure can be increased? Time is a critical factor because the holes will grow in size. It appears that using a liquid back pressure alone has not worked and may be accelerating the rate of erosion of the holes in the riser.
7) Therefore, BP is attempting to use small solid objects (junk, balls, whatever) inserted into the flow to in effect make the holes in the riser and/or passages through the BOP smaller. However, these solid objects are just as prone if not more prone to erosion by high pressure liquids as steel pipe. The challenge here is that the smaller the spaces come between the junk, the faster the mud and oil will jet through them and the greater the power of the mud and oil to cut through the junk. In theory, if the pathways through which oil is passing gradually and uniformly fill with junk and then the gaps between the junk are gradually and uniformly filled with mud, then the flow will gradually stop. The operative work here is “uniformly.” In practice, the junk may not be tough enough to keep from being eroded away by the mud and oil. Further, the blockages created by the junk and mud may not be uniform enough to prevent the oil and mud from forming a very high pressure flow through one or more pathways through the junk and mud in which the flows have sufficient force to cut through almost anything that might block such paths. High pressure liquids have a way of flowing through gaps and then making them bigger.
8) If many small solid objects (junk and mud) injected into the flow do not work to keep pressure from leaking into the ocean, then it is possible to stop the flow with fixed objects, such as valves, or by crimping the leaking riser pipe.
9) It is likely that crimping the riser is not possible because equipment does not exist to apply sufficient force at this depth of water, and even if it did exist, it is not clear that the damaged riser could withstand the force of the oil and gas. Any crimping action would need to be done gradually so as not to create a pressure spike. Further, if the crimp in the riser was not very tight, the oil and gas would continue to jet through the crimp and gradually make any gaps bigger over time. The BOP is essentially a big crimper designed to crush the pipe that comes out of the well. BP believes that it partially crimped the pipe through the BOP. Some have theorized that the jetting oil has eroded paths around the BOP's hydraulic rams.
10) So, the last remaining method of stopping the flow at the outfall with a physical object is to install a valve or valves to the top of the BOP. The valves would need to be open when a fitting is attached to the top of the BOP because otherwise the pressure would be too great to position and fasten something to the top of the BOP. Also, putting a closed cap on the top of the BOP risks creating a pressure spike. Any such effort would require removing the damaged riser first. If the existing crimp in the riser is slowing flows, this would also mean that oil would flow faster between the time that the riser was removed and a valve or valves were attached to the top of the BOP and closed. Again, such a valve system could not be shut off quickly without risking rupturing the well hole and steel pipe on which the BOP is anchored. So BP would need to attach a valve in an open position and then slowly close it. In theory the valve could be just above the BOP or it could be at the surface end of a pipe that is attached to the top of the BOP. The drill ship is supposed to have valves that could gradually slow the flow, but the pressure would be enormous and the operation dangerous for the crew (think a blowout on the drill ship, but an expected one). I am unsure whether a valve exists that could be installed at the top of the BOP, although some have suggested stacking a second BOP on top of the first and using it as a valve.
11) It is also possible to capture oil and gas in a dome of some sort (as was attempted), but the dome must be heavy enough or otherwise anchored firmly enough to not float away due to being filled with gas and gas hydrates (as happened with the first dome), and the pipe coming out of the dome must be big enough to accommodate a turbulent flow or oil and the flow of gas (that expands something like 150 times in volume by the time it reaches the surface), as well as any sea water that is sucked in along with the oil and gas. Think about pouring a volume of liquid that could flow smoothly through the narrow end of a funnel if it were poured exactly into the middle of the funnel. In reality, the liquid flow would not be so exact but instead would hit the wider part of the funnel, swirl around, and back up and ultimately overflow the funnel because turbulence would ensure that the flow in would exceed the flow out. Now trying do the same thing with shaken up soda - the bubbles would make the flow even more turbulent. A dome is essentially a funnel with the narrow end up. It’s outlet would need to be much larger than the pipe that is discharging oil and gas.
12) It is also possible to stick a pipe into the flow and collect some of it, but as with the dome, turbulence would limit flows into such a pipe unless it has a diameter that is much larger than the diameter of the leaking pipe. BP inserted such a tube into the end of the riser and captured some oil, but it is not possible to force a turbulent mix of oil and water into a pipe that is about the same size or smaller than the pipe from which the oil is flowing. In theory, one could add suction to a smaller pipe making it the hose end of the world's biggest shopvac, but it is not clear that sufficient suction could be generated and that a pipe large enough in diameter exists to collect the oil/gas/water mix.
13) BP has attempted the dome and flowing mud tactic, and is now attempting to block the flow with small physical objects in combination with mud, but the leaks in the riser seem to be getting bigger. BP has also attempted to capture some of the oil with a smaller pipe, but it could only collect a small proportion of the total flows. BP might have chosen these efforts because they were easier and/or less risky. The problem is that time is a critical factor. The longer BP waits, the bigger the holes get, the faster the oil spills, and the worse the spill gets. BP may have no choice but to remove the riser and attach some sort of fitting to the top of the BOP. Perhaps it should have bitten the bullet and done this immediately. Whatever technique it uses, it should minimize the time between when the riser is off and the fitting is attached.
14) It is also possible to stop the flow underground through kill wells, but this will take time because a kill well needs to intersect the blow out well hole near the oil reservoir thousands of feet under the surface of the ocean.
My idea is to attach a Y valve at the top of the BOP, one side of which would empty into the sea and the other attached to a riser that goes up to the drill ship. Once the Y valve was attached, the flow could be gradually directed to the drill ship, which would release some of the pressure by separating and flaring the gas and collecting the oil. As the drill ship crew got a handle on the flows, the Y valve could increasingly divert flows to the surface, to a point where hopefully the drill ship could collect the entire flow and then gradually stop the flow. Yes, oil would flow into the ocean for a while, but that's what's happening anyway. The only other choice would seem to be to send the entire flow to the drill ship all at once, which would risk a second Deepwater Horizon type explosion.
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