Underwater mudslides are the biggest threat to offshore drilling, and energy companies aren’t ready for them

Like generals planning for the last war, oil company managers and government inspectors tend to believe that because they survived the 2010 BP Deepwater Horizon oil spill, they are ready for all contingencies. Today they are expanding drilling into deeper and deeper waters, and the Trump administration is opening more offshore areas to production.

In fact, however, the worst-case scenario for an oil spill catastrophe is not losing control of a single well, as occurred in the BP disaster. Much more damage would be done if one or more of the thousand or so production platforms that now blanket the Gulf of Mexico were destroyed without warning by a deep-sea mudslide.

Instead of one damaged wellhead, a mudslide would leave a tangled mess of pipes buried under a giant mass of sediments. It would be impossible to stop the discharge with caps or plugs, and there would be little hope of completing dozens of relief wells to stop discharge from damaged wells. Oil might flow for decades.

This scenario has already occurred, and we are seeing the results at a well off Louisiana, owned by Taylor Energy, that has been leaking oil since 2004. Based on this disaster and my 30 years of experience studying deep-sea oil and gas seeps, I believe that regulators and energy companies should be doing much more to prevent such catastrophes at other sites.

Active leases for oil and gas drilling in the Gulf of Mexico. BOEM

Underwater avalanches

The mudslide that caused the Taylor Energy leak was not an isolated event. Many major features of the Gulf of Mexico’s continental slope – where the sea bottom descends from the continent’s outer edge down to the deep ocean floor – were formed when that slope failed. Their bathymetric contours show unmistakable signs of massive mudslides in the past.

Despite generations of oil production, the sedimentary strata of the northern Gulf still harbor billions of barrels of oil. The modern, loose material that lies atop these rock layers is also susceptible to failure, which generates a phenomenon known as turbidity currents. These are massive avalanches of sliding material partly suspended in water, which can travel for miles with astonishing speed.

One of the most famous turbidity currents occurred in 1929 following a 7.2 magnitude earthquake centered near Newfoundland’s Grand Banks. The resulting slide displaced over 40 cubic miles of material, traveling at 50 miles per hour for up to 300 miles.

Turbidity currents can be caused by earthquakes, collapsing slopes and other geological disturbances. Once set in motion, the turbid water rushes downward and can change the physical shape of the seafloor. NOAA

Drilling on shaky ground

In 2004 storm surge and monster waves from Hurricane Ivan initiated the huge mudslide that destroyed the Taylor Energy platform, an aging facility called MC20A, located about twelve miles off the Mississippi River’s Birdfoot Delta. Company engineers claim it had only three flowing wells before it was toppled. Its wells were equipped with subsurface safety valves that were reportedly closed off when the platform was evacuated ahead of the storm.

These valves apparently failed, because miles-long oil slicks have been seen on the waters above ever since the 2004 mudslide. Despite years of effort and expenditure of more than US$230 million, oil is still flowing from beneath the legs of the downed platform at a magnitude I estimate to be at least 100 barrels per day. This event is the longest oil spill in U.S. history.

In deeper waters, modern platforms are specifically designed to resist hurricanes. However, earthquakes also occur in the northern Gulf. The National Earthquake Information Center had recorded eight earthquakes in the region prior to 2009, with magnitudes ranging from 3.2 to 5.9. On May 6, 2018 a magnitude 4.6 event occurred at a depth of 6500 feet.