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Drilling Hazard

Drillinghazard
A new study from the UT Jackson School of Geosciences looks at the complex geology that contributed to
the Deepwater Horizon disaster.

A study from the UT Jackson School of Geosciences is the first published in a scientific journal to take an in-depth look at the challenging geologic conditions faced by the crew of the Deepwater Horizon drilling rig and the role those conditions played in the 2010 disaster.

The well blowout killed 11 people and spewed oil for three months, spilling about 4 million barrels of oil into the Gulf of Mexico before crews successfully capped the well. Researchers and investigators since then have focused mostly on the engineering decisions and mistakes that led to the blowout and the ecological effects of the oil spill. But researchers from the Jackson School, aided by thousands of pages of documents made public during lawsuits and legal proceedings, have pieced together how the geologic conditions more than 2 miles under the Gulf floor made drilling difficult and drove engineering decisions that contributed to the well’s failure and the ensuing blowout.

The study, published May 7, 2019, in Scientific Reports, documents, among other things, a significant and steep drop in pore pressure inside the rock near the bottom of the well that influenced the decisions that contributed to the blowout.

“The paper tells the geological story behind the catastrophe,” said Will Pinkston, who authored the paper while earning a master’s degree at the Jackson School. “It is high impact science, and I’m excited to reach a wider audience.”

In the case of the Transocean Deepwater Horizon drilling rig, which was operated by the BP energy company at the time, the pore pressure was very high throughout the well, but dropped abruptly by about 1,200 pounds per square inch near the bottom. Most of the pore pressure drop occurred in the 100 feet above the reservoir target of 18,000 feet below sea level.

BP planned to temporarily abandon the oil, plugging the well base with steel and cement until it could be produced at a later date. However, the sharp drop in pore pressure, and an associated decline in stress, drastically narrowed the range of options to seal off the well. This led to the decision to use a controversial low-density foam cement that failed to set properly. This was a key cause of the blowout.

“The bottom line is that the geological conditions led to a decision to use a specialized cement that failed,” said Peter Flemings, a Jackson School professor and senior research scientist at the Institute for Geophysics and study author. “This decision was a root cause of the ultimate blowout.”

Flemings was a member of the Deepwater Horizon well integrity team assembled to help respond to the disaster by then U.S. Energy Secretary Steven Chu.

The paper also maps geologic conditions across the entire subterranean basin to show that the pressure drop was not a unique event in that area. And although the paper does not pinpoint any single reason for the catastrophe, Flemings said it offers important information for the larger drilling community.

“One of the significant things about this paper is to get all the data on the table so that the general community can understand the decisions that were made,” he said.