During my youth I was a drilling engineer and thought the comments below may interest you and future news will judge its validity. Please note I am the dinosaur in the new era of mammals with regard cutting edge technology. However, as you clearly practice, logical first principles should remain relevant.
I have based my conjecture on this article:
Points of interest:
“Production string” – suggests it was the 7” or 5” casing that was cemented.
“Halliburton had completed the cementing of the final production casing string in accordance with the well design approximately 20 hours prior to the incident” – they are implying they pressure tests to determine zonal isolation to “industry” standards were done satisfactorily AND 20 hours was enough time to assume the cement set properly. Plus the BP drilling engineer approved the design and program then signed off. Halliburton is preparing their legal liability defense.
Please note Halliburton was also responsible for the cementing of the last year's huge West Australia spill. Root cause of this spill was determined (and reported on MARCH 15, 2010) to be .... wait for it..... Failure to test a cement casing .... hmmmm.
“At the time of the incident, well operations had not yet reached the point requiring the placement of the final cement plug…” – the fly in the ointment detrimental to Halliburton.
Halliburton cementation engineers on the Montara Well Blowout in Western Australia was inept in calculating volume and the Oil Company’s drilling program planning bad because the rig had no properly sized blowout preventers (BOP) on board when the accident occurred.
It’s obvious the BOP on the Deepwater Horizon failed because it could not control the “gas kick”.
All oil rigs, when they begin, have this explosive blow out potential because the gases are trapped for many eons and will escape very suddenly if there is any break in the salt overlays that often seal off offshore oil and gas fields. Most of these carbon deposits are ancient dead sea life and so, are often sealed by water evaporating during various warming cycles of our planet and then covered with mud layers when the oceans rise during cooling phases. And yes, our planet sees many such cycles, it doesn’t have any theoretical ‘stable point’ but rather, is a pendulum that swings back and forth.
The cement slurry design may have been ok for the job when argued against data for other wells drilled in the area – but not conclusively proven. What is real the gas got thru. I assume the well was drilled underbalanced drilling system because deep wells in deep water have complicated parameters.
The sequence of events suggests human error.
It is possible the cleaning of the formation surface was inadequate (therefore nuisance gas channel flows occurred to compromise zonal isolation);
Perhaps the wiper plug did not work well enough to clear the “mud” thereby compromising zonal integrity.
I am inclined to argue the slurry design was not good enough and this raises the question on what down-hole measurements and logs were used to analyse the formation to be cemented?
Why did the BOP fail? Was incorrect sizing, lack of equipment maintenance, bad design?
Some Technical background:
Deep water drilling generally creates unique problems because of the following:
. The subsurface and deepwater depth (with its greater number of geological formations and the hydrostatic weight of the sea column) of the intended well may force the driller to set large diameter casing in poorly consolidated formations or zones. These types of formations generally have a narrow pore-fracture pressure window with a high potential for shallow-flow water or gas hazard (formation fluid or gas easily flows out of the formation into the annulus.
· The low temperature at the sea bottom and the first several thousand meters below the surface or mudline.
· Then there are the mechanical complications because the subsea wellhead (resting on the seafloor) makes launching cement wiper plugs (plug to wipe mud off internal inner diameter of casing + push the cement downhole because the wiper plug is pushed downhole by mud with cement below the wiper) etc difficult. Plus the subsea well head makes any remedial work more difficult.
· Abnormally pressured sands, with high probability shallow-surface water/gas flows is typical problem. Uncontrolled shallow flows in the cementing affect the integrity of the well. Such uncontrolled shallow flows are:- subsidence, compromised seafloor stability, loss of well support and buckling of structural casing, compromised well bore integrity etc.