Trying to Make Sense of the Gulf of Mexico Disaster

I have trawled the web in my attempts to understand and make sense of the Gulf of Mexico oil leak disaster. I still do not understand it and I would like more information to help me to understand it. As a Mechanical Engineer I feel professional shame. Engineers learn from disasters and it will be very important to learn all possible lessons from this one.

The original explosion and fire on the Deepwater Horizon platform cost human lives. It would not be acceptable to continue such operations in the same manner until the mechanisms involved in this disaster are understood and appropriate measures can be taken to address them and assure the safety of personnel when there is a sudden major surge of methane gas.

It seems to me that the environmental damage is huge. It will be a long time yet before the true extent of that damage can be quantified. I do not wish to over-dramatize this either. While it is no consolation to those who have lost loved ones, those directly affected in myriad ways and those who are deeply concerned, Mother Earth is capable of taking the hit, which is not to say that she will remain unchanged and undamaged. In the long history of the Earth I feel sure there must have been even greater natural releases of crude oil from beneath the sea. However, this does not excuse any failure to take all appropriate precautions and all appropriate remedial actions.

A blow-out was to be anticipated sometime, as blow-outs have previously occurred many times and are well documented. Lessons have been learned from previous blow-outs and this present disaster is the first of its type. Presumably the blow-out preventer that was installed contained multiple levels of redundancy. Nonetheless, it could have been envisaged that the blow-out preventer might have failed. What were the intended steps to be taken in such an event? They may have included ‘top kill’, the placing of a heavy capture dome, the placement of a lower marine riser package (LMRP) cap and the drilling of interceptor wells. Henceforth, these will be inadequate contingency plans. Undoubtedly, oil companies and regulators will take this on board.

In what ways did the blow-out preventer (BOP) fail? Did the hydraulic actuators or mechanical drives fail to move the rams that would seal the bore of the BOP? Was there a freezing effect, owing to the expansion of dissolved gas, that locked everything solid? Methane hydrate (an ice of water and methane) seems to be implicated in the various phenomena associated with this disaster, whether within the oil and gas reservoir, within the well riser, within the BOP, in throttled flow or within jets of pressurized oil and gas that mix with seawater.

BP have published a graphic of the LMRP cap. I do not understand why it has been impossible to achieve a leak-tight seal. It seems the pipe emerging from the BOP was cut with a diamond wire saw, but the cut may have been finished with shears, which would have left a surface that was not ideal for sealing. Perhaps a tool could be made that would allow this surface to be ground down to the necessary flatness. Given that there is a flange at the top of the BOP it should be possible to apply enough clamping force to achieve a seal. As a mechanical engineer I find it extremely disappointing that, given the time that has elapsed, it has not been possible to achieve a leak-tight seal at the top of the BOP.

I’m not quite sure, but it seems it has been possible to insert coiled tubing into the well riser. I do not see why my own idea of inserting a long, heavy taper into the well riser could not be considered: it would require modifications to existing technology. The taper I envisage would be constructed from standard drill pipes of increasing diameters. Taper couplings to go between these could be manufactured quickly. It could be weighted with drilling mud, perhaps even with the addition of steel or lead balls. Such a system would allow a well to be plugged relatively quickly, stemming the leak until the well riser had been intercepted at a low level. Perhaps there is a fear of allowing unrestricted full-bore flow while preparations are made for the insertion of the taper. This may be a valid objection, but it could be checked-out. My impression is that this may be a self-choking flow, which may have been very close to full-bore choked flow just after the pipe was severed above the BOP by sawing. Is it possible to fully unrestrict the full bore of the BOP by moving the rams outwards? I don’t know.

I am not aware of the state-of-knowledge of high pressure two-phase flow, as it relates to this disaster, but it seems there is an urgent need for a detailed understanding of how the flow develops within the well riser. From my own experience of refrigeration it seems that there is some analogy between the well riser pipe and the capillary tube used in refrigerators. In refrigeration the flowing liquid changes phase, whereas in a pipe containing oil and dissolved gas the gas may come out of solution. The maximum mass flow rate is determined by the possible flow of liquid, but the emerging flow will tend to be choked two-phase flow. The analogy stops there.

The major additional factor in the case of the well riser is that the pressure seen at the floating platform can vary by roughly the full hydrostatic head of the entire column of oil. At one extreme the entire riser could be filled with pressurized gas, while at the other it could be filled with liquid. As total depths have increased this has become an increasing problem. Where the BOP cannot be fully closed, as is still the case in this disaster, it can be impossible to inject heavy fluid from the top. A taper could perhaps be inserted.

I just have a hunch that in the long run a (nearly) full-depth heavy taper within the production bore might provide a means of managing the extremely variable two-phase flow conditions of wells such as that in the Gulf of Mexico.

Engineers may also need to consider ways of providing a liquid and gas separator at a depth close to the reservoir. This could allow separate risers for liquid and gas to be used. Theoretically an ideal riser through deep water for liquid or gas would incorporate self-acting throttle restrictors that would would maintain a pre-determined excess pressure over the hydrostatic water pressure within the riser. Delivery at the floating platform would occur at modest pressures.

It strikes me too that hard questions need to be asked and answered about the ability to permanently seal abandoned deep water oil and gas wells. Extremely serious though this disaster is, even worse disasters need to be contemplated. There have been some suggestions that explosives (even nuclear explosives) be used to try to block the leaking riser. Wisely, I believe, this approach has not been judged appropriate. One could imagine uncontrolled flow through a damaged well riser eroding the riser and eventually providing a large bore communication between the reservoir and the seabed. What are the contingency plans if this were to happen?

In meeting the needs of the Earth’s growing population and humanity’s growing total appetite for energy there are no easy answers and there are global-scale risks with large scale harnessing of energy, no matter what the source. In my view there is a need to pursue all technical options in search of the best compound solution, but with due diligence and an appreciation that the one Earth is a shared resource of all of humanity.