[US] Delta House FPS Subsea Jumper Leak

escveritas
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[US] Delta House FPS Subsea Jumper Leak

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Executive Summary

Between the evening of October 11 and the morning of October 12, 2017, a fractured subsea wellhead jumper that connected the Mississippi Canyon (MC) 209 SS001 wellhead to a subsea manifold referred to as a PLET (Pipeline End Termination) released an estimated 16,000 barrels (bbls) of oil into the Gulf of Mexico (GOM).

The failed subsea wellhead jumper, designated as KAA-0120, Pipeline Segment Number 19174, operated at a water depth of 4917 feet within MC Block 209. The subsea well is part of the Neidermeyer Subsea System. The subsea well is tied into additional subsea lines flowing to the topside semi-submersible facility A (Delta House), located at MC Block 254, and operated by LLOG Exploration Offshore, LLC (LLOG).

LLOG shut in the Delta House platform on October 6, 2017, in preparation for the evacuation of personnel ahead of Hurricane Nate. Personnel returned on October 10. When ramp up for operations began that evening, operators observed the KAA-0120 flowline pressure measuring below hydrostatic pressure. This indicated to the operators that the flowline had integrity.

By the morning of October 11, Delta House Control Room Operators (CRO) began to observe that rates from the Multiphase Flow Meter (MPFM) installed on the KAA-0120 flowline did not match rates measured at the Lease Automatic Custody Transfer (LACT) meter. During the startup process, it is common for flow meter discrepancies to be noted for several hours until the well achieves a stabilized flow of fluids. The CROs also observed flow rate discrepancies at the top side separator meters. Delta House operators began to troubleshoot the meters both topside and subsea as a matter of course but did not suspect a loss of pipeline integrity.

A Level Safety High (LSH) indication from the Sump Tank shut-in the facility which interrupted the initial startup process. Operators subsequently reinitiated the startup process. Additionally operators on Delta House had to decrease oil export rates due to an issue at a downstream facility, Viosca Knoll (VK) Block 817 that receives oil from Delta House.

By the morning of October 12, operators at Delta House, after communicating with onshore LLOG personnel, concluded that all of the meters were working properly but still showed a discrepancy of approximately 5000 barrels. When the system achieved steady state flow, the operators compared various trend data to historical start-up trends and identified temperature and pressure drops. Concerns of a leak in the flowline began to escalate, and both the MC 209 SS001 and MC 208 SS001 wells were shut-in.

Delta House operators began to isolate the MC Block 209 SS001 well by remotely closing manifold valves. The subsequent observations indicated that the pressure at the flowline jumper or infield flowline was hydrostatic signifying a leak.

On October 12, LLOG conducted a visual inspection of the MC 209 flowline using a Remotely Operated Vehicle (ROV). The inspection confirmed that the jumper connecting the MC 209 SS001 wellhead to the PLET cracked at the base below the MPFM. On October 13, BSEE Investigators photographed the sheen during a flyover on the way to initiate an onsite investigation (see Figure 1). Ocean currents flowed to the South West at the time of the incident and away from the coast. No reports stated that oil attributed to the leak reached the shore.
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