The Oil Spill: Anatomy of a Blowout (and How It Will Happen Again)



It seems we've learned at least one thing from the continuing oil spill in the Gulf of Mexico: whatever you do while drilling for oil, you should always, ALWAYS run a cement-bond log.

What the heck is a cement-bond log? It's a very standard safety procedure that drilling engineers have known about for years. It's considered crucial to running a safe oil well, and it was not performed in the hours leading up to the explosion of the Deepwater Horizon platform on April 20.

In short a cement-bond log, coupled with insufficient amounts of cement used in the drilling process, may be the reason untold thousands of barrels of oil are gushing into the Gulf of Mexico right now.

According to an analysis on The Oil Drum of the final hours before the explosion, the drilling crew knew something was amiss. Drilling fluid was leaking out the bottom of the well, indicating an area of low pressure. This is normal, but it requires an additional step — the cement-bond log, basically taking measurements inside the borehole to make sure the cement is solid — to ensure that the well casing is safe from any gas that could leak up the sides of the well and burst in, according to Oil Drum contributor and geologist Arthur Berman:

Mud had been lost to the reservoir while drilling the bottom portion of the well (this is called “lost circulation”). It usually indicates good reservoir quality, an interval of lower pressure or both, and can result in an enlarged wellbore or “washout”. The significance of this is that it might have been difficult to create a good cement seal between the casing and the formation. It also would have been impossible to ensure the effectiveness of the cement seal without running a cement-bond log, and this was not done. (emphasis added)

Building a cement sheath around the borehole is a critical step in any well for creating a safe environment for extracting oil and gas.

Here's the scary part: Berman notes that 51 barrels of cement were used in construction of the well, not nearly enough create a seal safe and strong enough to hold back the pressure of the surrounding reservoir. And wells all over the Gulf of Mexico are planned in similarly unsafe ways. Berman further writes:

What can be addressed now is the larger issue that a flawed, risky well plan for the MC 252 well was approved by the MMS, and BP, Anadarko and Mitsui management. Similar or identical plans were undoubtedly approved and used by many operators on other wells drilled in the Gulf of Mexico. A plan that does not include enough cement to overlap the final and previous casing strings, and that does not require running a cement-bond log to ensure the integrity of the seal is a defective plan. The fact that there have not been blowouts on previous wells does not justify the approval and use of an unsafe plan.

Well, Berman wrote his analysis on Friday, so he probably didn't know that there have in fact been many blowouts in the Gulf of Mexico — at least 38 of them, in fact, between 1992 and 2006. In a little less than half of those cases, the Minerals Management Service listed the cause as "poor cement job."

Wait, what? There have been close to 40 blowouts just in the Gulf in a 14-year period, and no one thought to revise drilling procedure?? Yep, pretty much (there are nearly 4,000 active platforms in the Gulf, but still).

In fact, an investigation by the Associated Press pointed out that the cements used in state and federal highways around the country are subject to far more stringent standards than the stuff designed to prevent explosive methane gas from exploding up from thousands of feet beneath the sea.

Just to put this all in a little bit of context, sprinkled in above and below are components a terrific graphic from Information is Beautiful that shows just what's at stake with this oil spill (it's size is a very, very conservative estimate). Pay particular attention to the amount of time we have left as a world utterly reliant on oil:

Images: The Oil Spill in Context, Information Is Beautiful

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