Sunday, February 20, 2011

Cause of Gulf blowout remains only partly known

Unlike the Final Report of the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, the Chief Counsel's Report, released February 17, 2011, provides some technical analysis of the disaster, along with new information. [1] The most striking new information discloses that, after cementing, the Macondo well reservoir of oil and gas under very high pressure was left with a potential channel into the well's production casing through an open float collar. It confirms that blowout oil, gas and sand flowed upward inside the casing rather than through the annulus around the production casing, as most early descriptions had estimated.

The Chief Counsel's Report describes some steps performed after the July 15, 2010, actions that ended the flows of oil and gas. BP personnel, using Development Driller II, recovered an upper section of the production casing, the attached casing hanger and samples of annulus contents [p. 43]. The annulus samples had low hydrocarbons, and the outside of the casing hanger showed no erosion [Fig. 4.1.4], indicating that blowout flow did not occur in the annulus between the production casing and outer casing. The inside of the casing hanger showed severe erosion, indicating that abrasive blowout flow traveled inside the casing--evidence that appears conclusive.

Unless there was a downhole rupture in the production casing, blowout flow ran through the casing shoe. Evidence cited in the Chief Counsel's Report shows that check valves in a float collar above the shoe probably failed to activate and interrupt back-flow [pp. 88-90]. A mud flow rate was never measured that would have been enough to displace the auto-fill tube propping the check valves open. Pressures applied while trying to displace the auto-fill tube may instead have broken some element of the casing string. The check valves would not have fully sealed out oil and gas flow, but they would have reinforced the shoe track cement barrier, had they been closed.

Although the Chief Counsel's Report does not describe pressure balances, displacing about 3,300 feet of drilling mud with seawater, following the cementing operation, left over 1,200 psi of pressure difference on shoe track cement. Highly foamed cements may achieve less than 2,000 psi compressive strength, and the foamed cement used for the Macondo well may have been unstable. Three out of four laboratory tests performed by Halliburton and nine out of nine tests later performed by Chevron, as requested by the National Commission, showed instability, resulting in porous structures with low strength. A collapse of shoe track cement, unrestrained by check valves, could have allowed oil and gas to enter the production casing.

The Chief Counsel's Report has been criticized for preparation by lawyers rather than engineers. However, the National Commission and its staff were both headed by lawyers. No working engineers served on its staff. Its assistant staff director was an economist. Its "senior scientist" had been communications network manager. The commission did not form an advisory team of engineers and scientists. Its access to practical and scientific knowledge and assessment of deepwater drilling was very limited. Out of its 85 named consultants, only one is a petroleum drilling engineer, currently working as an independent. One is a petroleum chemist. One is a former Interior Department oil and gas well regulator. Three are petroleum engineering professors, all from the same university. At least 30 of the named consultants are lawyers, and at least 40 are policy analysts.

Despite an order from President Obama stating it would be "focused on...environmental and safety precautions," the National Commission focused on determining responsibility for the disaster. About half of the commission's Final Report describes background and events of the disaster, detailing who did what and when. [2] Those issues are critical when determining comparative negligence for settling damage claims, but they are peripheral to a technical analysis of how the Macondo well blowout occurred. The Chief Counsel's Report amplifies the emphasis on assigning blame, providing an essentially forensic analysis of events, illustrated by a company that serves trial lawyers by preparing exhibits. It is mainly fortuitous that forensic analysis resulted in public release of new technical information.

The Chief Counsel's Report lodges more responsibility for the disaster than was previously clear with haphazard cement preparation and testing by Halliburton [pp. 121-123]. It gives no explanation for a discrepancy between laboratory test conditions and downhole conditions. The report shows a plastic test cell for foamed cement, with brass fittings [Fig. 4.4.3], probably rated for no more than 1,000 psi. Downhole pressures were around 13,000 psi, substantially compressing foam bubbles and resulting in cement densities higher than specified and higher than measured by laboratory tests. The report cites several obstructions by Halliburton to investigations: providing irrelevant references to industry standards [p. 120], refusing to provide company documents [pp. 118, 120 and 121], refusing to describe test methods [p. 119], refusing to provide materials for third-party testing [p. 119] and refusing to provide testimony by company personnel [pp. 118, 120, 121 and 122].

The main likely impact of the National Commission's work will be to help defend whatever penalties the federal government levies against BP, Transocean and/or Halliburton for the disaster. Much of the Chief Counsel's Report could populate a trial brief, for use in a lawsuit challenging the penalties. A major opportunity was lost to examine the cause of the blowout while evidence was fresh.

[1] National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, Chief Counsel's Report, February, 2011, available from .

[2] National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, Final Report, January, 2011, available from .