For the past 70 to 80 days, a meander of the North Atlantic gyre has put offshore drilling on hold for many deepwater drilling rigs within the Green Canyon, Mississippi Canyon and Walker Ridge regions of the Gulf of Mexico.
According to Matthew Cadwallader at Horizon Marine, a Marion, Massachusetts-based firm that tracks and monitors ocean currents for the offshore industry, currents up to 4.3 knots have been recorded in some of the most densely-populated offshore oil fields in the Gulf of Mexico.
Cadwallader notes the eddy “Lazarus,” as its named, was formed in early July and reconnected to the Loop Current in late August. It remains connected and today it’s western limit extends to 91° 45’ W.”
For the plethora of deepwater rigs working in the area, the strong current has completely shut down operations as the drilling risers, pushed hard over by the currents, have exceeded their environmental limits. In addition, the currents, sweeping past these cylindrical tubes (risers), create vortex induced vibrations (VIVs) which in at least one case, required a rig to unlatch from the blow out preventer (BOP) on the sea floor.
In another case, a gCaptain source notes a deepwater rig was forced to unlatch their Lower Marine Riser Package (LMRP) from the BOP, but still had to install a packer inside the riser and then fill the riser with 16 pound mud in order to keep the riser under tension and as vertically-oriented as possible. This particular rig has seen over two months of downtime while waiting for the current to subside.
Besides the technical issues of vibrations and riser angles, the Loop Current has cost offshore operators hundreds of millions, if not billions of dollars in unplanned rig downtime. For each rig, a rough estimate of a million dollars per day has been shaved off the bottom line for each well that was being drilled in the area.
For production rigs such as BP’s Thunderhorse and Mad Dog, Chevon’s Tahiti spar, or BHP Billiton’s Shenzi and Neptune rigs, the current has left those rigs largely unaffected as the design of those rigs and associated risers take into account the affect of heavy current conditions.