January 14, 2005 – Shell Offshore Inc. (Operator) & Transocean Offshore (Contractor)

Remarks: Prior to the incident, during drilling operations in Atwater Canyon 267, the rig crew on the Transocean Deepwater Nautilus semi-submersible drilling rig transferred Internal Olefin Base Oil (IOBO) from the work boat C Legend to the Deepwater Nautilus. The IOBO was pumped to pits #'s 1, 2 & 3. The transfer was successfully completed and pumping to the column tank was initiated. A couple of hours later when the pump man checked the levels on the pits he found the #2 pit to be almost empty. The leak point was identified as the dump valve on #2 mud pit on the Deepwater Nautilus. It was determined that a small piece of rope was lodged under the dump valve preventing a proper seal and resulting in a leak path. Human Error was determined to be a contributing factor because: a) prior to pumping operations the pre-inspection of the valve was not properly preformed; b) there was a lack in valve inspection procedures to insure that the valve would close and seal properly; and c) there was no post watch of the pits during (OIBO) pumping operations to insure that leakage would not occur. It is estimated that approximately 156 barrels IOBO synthetic base oil had been released into the Gulf of Mexico.

Accident Investigation Report: Form 2010 14-Jan-2005 AT267

NRC Report: 747131

February 25, 2005 – Murphy Exploration & Production Co. (Operator)
& Transocean Offshore (Contractor)

Remarks: Sea Conditions: Winds 23 mph, Current 6 mph, 6 foot seas. During drilling operations in Mississippi Canyon 734, the derrick man on the Transocean Marianas semi-submersible drilling rig had transferred 170 barrels of MIDF synthetic base oil from pit #2 to pit #3 in order to clean pit #2. The cleaning operation was incomplete at the time shift changeover occurred. The derrickman communicated to his relief that the dump valves were still open. The relieving derrickman felt the pits needed additional cleaning but after doing so failed to close the dump valves. The following morning, the derrickman started transferring MIDF synthetic base oil mud from pit #3 pit back to pit #2 but failed to remember he had not closed the valves the night before. After starting the transfer the derrickman was required to do a second task. Later on, the mud engineer checked pit #2 and found no mud in the pit. Approximately 170 barrels of MIDF SBM were released into the Gulf. It is estimated that 150 barrels were Novaplus B synthetic base oil and 20 barrels were RHEFLAT drilling fluid additives. Findings: Failure to follow Transocean NO SOBM Spills Plan; Failure to follow Transocean Specific Think Procedure for transfer of fluids (step 3 would have checked the disposition of the overboard dump valve); and the derrickman was performing a second task while SOBM was being transferred.

Accident Investigation Report: Form 2010 25-Feb-2005 MC734

NRC Report: 751054

 February 28, 2005 – Shell Offshore Inc. (Operator) & Helmerich & Payne, Inc. (Contractor)

Remarks: Sea Conditions: Winds N at 10 mph, Currents SW at 3 mph, 3 foot seas. Platform rig H&P 201 crew was performing cementing operations on a liner on Well A-14 sidetrack 03. in Mississippi Canyon 807. When circulating bottom up, a larger amount of cement returned to the surface than expected. The pressure increase was misinterpreted when the second isolation ball entered the smaller pipe. The interface was diverted to the Gulf to keep the cement out of the pits. When the contaminated fluid got to surface, the fluid engineer and the foreman on tour planned on dumping the interface which is usually less than 20 barrels. This procedure was understood by the operator to be an acceptable practice. The operator's acceptable practice for dumping the interface (usually less than 20 bbls of SBM) may be in question. The operator did not have a contingency plan to prevent synthetic base mud from entering offshore waters during cementing operations. In this particular case they dumped 280 barrels before diverting the fluid back to the pits. This resulted in approximately 204 barrels of of 54% synthetic-based mud (SBM) and 76 barrels of cement entering into the offshore waters. It is estimated that the lost SBM contained approximately 110 barrels of synthetic base oil.

Accident Investigation Report: Form 2010 28-Feb-2005 MC807

NRC Report: 751356

March 11, 2005 – LLOG Exploration Company (Operator) & Diamond Offshore (Contractor)

Remarks: On March 11, 2005, at 1300 hours the wellhead connector on the BOP Stack on the Diamond Offshore Ocean Saratoga semi-submersible rig (working for LLOG Exploration in Green Canyon 157) inadvertently unlatched due to improperly connected Blowout Preventer control lines. The well had production casing set, a subsea tree installed and the last in-hole operation prior to the incident occurring was to perforate the production interval. This is an oil producing reservoir and the rig was in 2,614 feet of water. Upon the Wellhead Connector unlatching, the differential pressure between the weighted completion fluid in the riser and the normal seawater pressure caused the stack to separate from the wellhead profile on the top of the subsea tree. The fluid level in the riser equalized to the seawater hydrostatic. Approximately 500 barrels of calcium chloride completion fluid (14.2 ppg calcium chloride salt water) were released from the riser.

In summary due to poor procedures and human errors the hoses were crossed on the wellhead connector for the Yellow Pod circuit. Several opportunities to correct the above errors were missed. The hoses to the Yellow Pod were not installed properly and were not detected during the shipyard shake out inspection. The Subsea Function Test Checklist Procedures failed to detect the improper operation when testing the BOPs in the moon pool. A further opportunity to detect improper operation of the connector was missed during the landing and latch up operations on the seafoor. A miscommunication between the Subsea Engineer and the assistant Subsea Engineer during the function verification process as to the position of the latch indicator on the H-4 type connector when switching from the Blue to the Yellow Pod was a contributing factor to the cause of this incident.

Accident Investigation Report: Form 2010 11-Mar-2005 GC157

NRC Report: 752472

July 5, 2005 – Anadarko Petroleum Corporation (Operator) & Ensco Offshore Co. (Contractor)

Remarks: Sea Conditions: Winds S at 70 mph, Current S at 4 mph, 15 foot seas. On July 5, 2005, while the Ensco 7500 semi-submersible drilling rig was engaged in drilling activities in Green Canyon 652, an unplanned riser disconnect was initiated because of unfavorable sea and wind conditions associated with an approaching tropical depression. While the riser volume was being displaced with seawater in preparation for the disconnect operation, the rig was no longer able to maintain station adequately enough to complete the operation. As a result, the riser was disconnected from the Lower Marine Riser Package (LMRP), at which time 710 barrels of 54% synthetic-based mud (SBM) was released from the riser into the GOM. At the time of the disconnect, there were no open hole hydrocarbons exposed below the casing depth. It is estimated that the lost SBM contained approximately 426 barrels of synthetic base oil.

Unplanned Riser Disconnect. Although the system was not yet a tropical storm, the Operator and Drilling Contractor had elected to suspend drilling activities at 21,715 feet at 1800 hours on July 4. Suspension of drilling activities occurred some 18 hours in advance of the incident. Personnel commenced circulating bottoms up to clean the well bore, and by 2300 hours started pulling the 6-5/8-inch drill pipe. All of the 6-5/8-inch drill pipe was out of the hole the next morning by 0830 hours (July 5, 2005). Personnel started to pulling the 5-1/2-inch drill pipe at 0930 hours; however, with the rig having difficulty holding position, orders were given at around 1000 hours to space out the 5-1/2-inch drill pipe in BOPE and hang off the pipe with 260,000 pounds on the upper variable bore rams (VBR) on the BOP stack. At 1100 hours orders, were given to displace the choke and kill lines, boost lines, and riser with seawater. At that time, the Rig heading was 12 degrees with seven thrusters working and six engines operating against winds out of the south at 61 knots and seas running 14 to 16 feet. According to the Contractor’s on-duty DP Operator during the morning shift prior to disconnect, the thrusters were operating at about 75-85 percent capacity with the engines running at 60-70 percent. Testimony from the DP Operator indicated that sufficient power to the thrusters was not the problem. The rig did not have enough thruster capability to hold location. He further indicated that one thruster was down for planned maintenance.

OCS Report MMS 2006-058: Investigation of Riser Disconnect and Spill, Green Canyon Block 652, OCS-G 21810, July 5, 2005

NRC Report: 764447

Hurricanes Katrina & Rita

Summary, Background, Spill Counts and Volumes  (Revised6/23/2008)

November 22 & 23, 2005 – BP Exploration & Production Inc. (Operator)
& Transocean Offshore (Contractor)

Remarks: Sea Conditions: Winds NE at 37 mph, Current S at 1 mph, 14 foot seas. November 21, 2005 at 1500 hrs - well had 60 bbls loss of fluids with no broaching at mudline observed by ROV. During drilling operations on the semisubmersible drilling rig Transocean Deepwater Horizon in Mississippi Canyon 126, a discharge of 59 bbls of synthetic-based mud (SBM) occurred as a result of loss of casing connectivity. With an unintentional back-off of both the 36" and 20 x 22" casing strings, the Synthetic Base Mud (SBM) inside the 20 x 22' casing string was broached to the seafloor during diagnostic and P&A operations. The following efforts were made to minimize losses to seafloor: (1) Immediate shut-in of blind rams when investigate original losses. (2) Displacement of choke, kill & riser to seawater prior to opening up. (3) Placement of P&A cement plug to minimize volume of SBM to be displaced while pumping job. (4) Immediate securing of well by P&A. November 23, 2005 at 1930 hrs - Displace mud from casing during P&A cement plug setting operations. Lost 286 bbls of SBM.

A total volume of 345 bbls of 61% SBM was lost in the Gulf of Mexico. It is estimated that the lost SBM contained approximately 212 barrels of synthetic base oil.

Primary causes were found to be: (A) Inadequate make-up torque on casing. (B) Poor cement job on surface casing string. (C) Possible poor alignment of rig.

NRC Reports: 780748 and 780340

THE SPILL BELOW IS A DRILLING MUD SPILL WHERE THE POLLUTION, SYNTHETIC BASE FLUID VOLUME, IS LESS THAN 50 BBL, BUT THE TOTAL MUD VOLUME WAS 50 BBL OR GREATER

May 14, 2005 – Remington Oil and Gas Corporation

Remarks: LESS THAN 50 BBL POLLUTION (but total mud volume greater than 50 bbl). Spill occurred of the lease. Oil-based drilling fluid spilled from a cargo tank of the offshore supply vessel Pecos River when the vessel was en route to deliver drilling mud to the Rowan Odessa jack-up rig in East Cameron 315. The spill resulted from the improper alignment of the mud tank valves during the circulation of the mud. The vessel's engineer had intended to circulate the starboard aft tank, but had accidentally taken suction from the port aft tank and pumped into the starboard tank. This caused the starboard aft tank to overflow through the vent line onto the deck of the Pecos River and into the Gulf of Mexico. An estimated 31 bbl of diesel was lost in the 50 bbl of 62% diesel oil-based mud (OBM).

NRC Report: 758749

One barrel (bbl) equals 42 U.S. gallons (gal)

Synthetic Oil Fluids*: In deepwater drilling, synthetic-based muds (SBM’s) are preferred over petroleum oil-based muds (OBM’s) due to the SBM's superior performance properties. The synthetic oils used in SBM’s are relatively non-toxic to the marine environment and have the potential to biodegrade.

60%**: Indicates that for a synthetic-based mud release, the exact percentage of volume of synthetic base oil to to total volume of mud released was not available and 60% was used as a reasonable approximation.

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Last Updated: 07/03/08, 08:10 AM