What caused the Deepwater Horizon disaster?

See the full post on The Oil Drum: http://www.theoildrum.com/node/6493#more

The blowout and oil spill on the Deepwater Horizon in the Gulf of Mexico was caused by a flawed well plan that did not include enough cement between the 7-inch production casing and the 9 7/8-inch protection casing. The presumed blowout preventer (BOP) failure is an important but secondary issue. Although the resulting oil spill has potentially grave environmental implications, recent efforts to limit the flow with an insertion tube have apparently been effective. Continuous efforts to slow or stop the flow include drilling two nearby relief wells that may intersect the MC 252 wellbore within 60-90 days.

1 Comment

  • Anonymous

    Thanks for posting this.

    However, my question is that you feel that the cause of the blow-out was a poor cement job up the annulus, due to a lack of cement, correct?

    My own calculations indicate that unless the hole was very badly washed out, more than enough cement was pumped to ensure a decent amount was in the 9 7/8″ x 7″ annulus.

    That doesn’t mean to say that it wasn’t channeled, allowing gas (or condensate?) to enter the annulus.

    However, that charts you present would not show anything awry if, as you theorise, all this was happening in the annulus as the annulus pack-off (seal) was in place and pressure tested – so there was no communication route between the well-bore and the annulus at that time.

    In addition, I doubt your explanation of the rapid increase in pit volume is correct, for two reasons.

    Firstly, the trip tank volume does not change until 20:30 hrs (when it actually drops) and secondly, the gas reading only goes to a maximum of about 75 units (only about 15,000 ppm) – if pure gas was coming up, there would be much, much higher readings.

    In addition, the casing diagrams have seen indicate that the next casing at surface was 16″, the burst of which is much less that the collapse of the 9 7/8″ of the tapered string.

    So wouldn’t any gas pressure in the annulus rupture the 16″ and therefore the blow-out would be much closer to the BOP Stack rather than very close to surface, which is what the photos indicate?

    If a poor cement job is the basic cause, wouldn’t it be possible that the inflow test which apparently failed, failed bacause of gas / condensate entering through the shoe track?

    Best Regards


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