February 9, 2007 – Hess Corporation (Operator) & Diamond Offshore Drilling, Inc. (Contractor)

Remarks: Sea Conditions: Winds SW at 6 mph, Current N at 1 mph, 2 foot seas. On the morning of February 9, 2007, drilling on the Diamond Ocean Baroness semi-submersible drilling rig was stopped to circulate the hole clean evaluate drilling after tar was noted in the mud returns. The mud engineer noticed that the mud pits were losing synthetic based drilling fluids (SBM). The rig jumped the ROV to check the riser and blow out preventers (BOPs) for possible loss of SBM. The ROV found a 5 to 10 foot long stream of SBM flowing out of a weep hole in the Lower Marine Riser Package (LMRP) at the riser flex joint. The well was immediately shut in at the BOPs using the annular. The level in the riser dropped 10 feet before stabilized and the leak stopped. The weep hole was later identified as a test port. The test port of the Flex Joint is used by the manufacturer for factory acceptance testing and is typically not a field serviced item. is the manufacturer of the flex joint, this design has been around for many years and this is the first known failure of this type. The cause of the leak was the failure of the threaded plug that was installed into the test port by the manufacturer of the flex joint. The tar in the fluid system could have created internal pressures in the flex joint which could have contributed to the failure of the threaded plug. Approximately 862 bbl of  14.9 ppg 53% synthetic-based mud (SBM) were lost to the Gulf of Mexico. It is estimated that the lost SBM contained approximately 457 barrels of synthetic base oil.

Accident Investigation Report: Form 2010 9-Feb-2007 GC468

NRC Report: 826044

June 23, 2007 – Stone Energy Corporation

Remarks: There had been several sheen reports in the Main Pass 288 area over several days. The sheens were investigated by Shell Offshore, BP Exploration, Stone Energy, United States Coast Guard, and Minerals Management Service. Four leaks were discovered approximately 900 feet away from Main Pass 288A platform. On June 23rd, a standup test was performed on the  16,000 foot long 4-inch oil pipeline segment #4582. Area Block 288 Platform A. Segment #4582 is a DOI-authorized pipeline in the Main Pass 288 and 289 areas. (This information is subject to change pending completion of the panel investigation.)

Panel Investigation Report: Pending

NRC Report: 839861

October 21, 2007 – Anadarko Petroleum Corporation

Remarks: During drilling activities on the semi-submersible rig Diamond Ocean Valiant began losing mud through the riser. A crack was found in the termination joint. Drilling operations were temporarily suspended for the riser to be removed and repaired. Approximately 1,929 bbl of  55% synthetic-based mud (SBM) were lost to the Gulf of Mexico. It is estimated that the lost SBM contained approximately 1,0161 barrels of synthetic base oil. No sheen was observed on the surface of the water. Using the ROV, it appeared that the SBM fell to the ocean floor. This information is subject to change pending completion of the 2010 District investigation.)

NRC Report: 852229

December 2, 2007 – BHP Billiton Petroleum (GOM) Inc. (Operator) & Global Marine Drilling Co. (Contractor)

Remarks: Sea Conditions: Winds WSW at 7 mph, Current NNE at 1 mph, 2 foot seas. On December 2, 2007 at approximately 1300 hours with well completion operations in process on the drillship GSF C.R. Luigs, the Dynamic Positioning Operator (DPO) was performing a routine preventive maintenance procedure for the Dynamic Positioning (DP) system when the riser Emergency Disconnect Sequence (EDS) was activated. The disconnect was below the Lower Marine Riser Package (LMRP) where it connects to the BOP stack on top of the wellhead and resulted in the discharge of approximately 550 barrels of Sodium Bromide brine into GOM waters.

Corrupted data was the cause of the Emergency Riser Disconnect. Once it was realized that there was corrupted data, the DPO and Captain  acted quickly. The DPO had never operated the DP system in an emergency situation and had not received DP simulator training. It has been determined that the erroneous data can be transferred during routine preventive maintenance procedures. The DP system did not give an indication that the corrupted data was transferred between consoles. The program logic that gives an alarm when erroneous data was transferred during routine maintenance was inadvertently omitted when the system was upgraded. This specific problem has not been seen previously with this system.

NRC Report: 863653

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 total volume of mud released was not available and 60% was used as a reasonable approximation.

75%***: Indicates that for an oil-based mud release, the exact percentage of  volume of base oil to total volume of mud released was not available and 75% was used as a reasonable approximation. Diesel is assumed to be the base  oil in OBM unless otherwise specified.