The Situation

M-I SWACO was asked by Shell Oil Co. to install, test and operate a HISIDE Mud Blender unit on the Leiv Eiriksson for use on their Gro Prospect.

The Shell Oil Gro Prospect is located in 4,590 ft (1,400 m) of water approximately 208 nautical miles off the Norwegian coast. It is in an area that has limited offset data and the use of the HISIDE Blender was recommended in order to maximize the chances of getting the surface pipe to depth in such an uncertain environment.

Planning called for the drilling of a 12 1/4-in pilot hole to a depth of 7,740 ft [2,360 m] prior to actual spud in order to assess the likelihood of shallow water flow and to retrieve pore pressure data. Once the pilot hole was completed, the rig would be moved approximately 195 ft [60 m] and the 12 1/4-in x 36-in x 42-in conductor hole would be drilled to approximately 4,920 ft [1,500 m]. After running the 36-in x 30-in conductor, drilling would resume with a 26-in hole being drilled to 7,740 ft [2,360 m] in preparation for the 20-in surface casing.

The Solution

The HISIDE Blender unit was installed and tested in December 2008. At that time, it was determined that the rig was unable to deliver the needed amount of seawater for effective operation of the unit. In January 2009, M-I SWACO installed a skid-mounted, electrically-driven centrifuge pump in the rig seawater line. The installation greatly increased the delivery of seawater to the unit. The unit was retested in January and proven ready for the rig to spud.

A total of 12,580 bbl (1,500 m³) of 1.97 s.g. kill mud was mixed with approximately 3,355 bbl (400 m³) delivered to the rig, 680 bbl [725 m3] held on the M/V Rem Provider and 3,355 bbl [400 m3] held on the M/V Foula Skandia. Also, approximately 3,355 bbl [400 m3] each of 1.35-s.g. and 1.45-s.g. KCL/Glycol mud was stored in the pontoon tanks of the rig. This mud was to be used to displace the hole once drilling was completed and the pipe was being pulled to run casing.

The Results

The 12 1/4-in pilot hole was drilled to a depth of 7,200 ft [2,195 m] using seawater and high viscosity sweeps. No shallow water flows were recorded. The hole was abandoned with 1.25-s.g. blended mud.

The 42-in conductor hole was drilled to a TD of 4,970 ft [1,515 m]. Seawater and high viscosity sweeps were used to drill all but the last stand of the hole. The last stand was drilled using 1.25 s.g. mud blended from 260 bbl [31 m3] of 1.85-s.g. kill mud and 705 bbl [84 m3] of seawater. The hole was displaced with 1.45-s.g. KCL/Glycol mud prior to pulling out of the hole to run the pipe.

Once the 36-in x 30-in conductor was run, drilling of the 26-in hole section commenced with seawater and high viscosity sweeps to a depth of 6,817 ft [2,078 m]. From that point to TD at 7,740 ft [2,359 m], pump and dump operations using the HISIDE Blender unit, were started. The blended mud was also used to work through tight spots encountered while making a short trip to 1,969 ft (600 m). During the return trip, the mud weight was raised to 1.32 s.g. at 7,503 ft [2,287 m] and the pipe was washed to bottom. The hole was then circulated for one and a half circulations with 1.35-s.g. KCL/Glycol mud prior to being displaced with 1.45-s.g. KCL/Glycol mud in preparation for running the casing.

A total of 9,921 bbl [1,183 m3] of 1.97-s.g. kill mud was blended with 25,600 bbl [3,053 m3] of seawater to make 35,525 bbl [4,236 m3] of 1.25-s.g. mud during the operation. Flow rates during the operation ranged from 5,250 L/min for the lighter weight mud to 5,000 L/min for the heavier weight mud. The 20-in casing was run to depth with no problems and the foam cement job was also conducted with no problems.

Benefits

The use of the HISIDE Blender unit enabled the client to safely and economically get the surface casing to depth in an uncertain environment. The ability to adjust mud weights in a quick and efficient manner allows the client to drill in these areas with a level of confidence that any problems can be dealt with quickly and efficiently. At the end of the running and cementing of the 20-in casing, the Gro Prospect was 17 days ahead of schedule. A great deal of that performance was due to the rig crews and the hard work they put in to overcome the problems that were incurred.