Southern Gabon Basin
Gabon’s Ruche offshore area accommodates the Ruche A (Ruche), Ruche B (Tortue), Ruche C (Moubenga) and Ruche D (Walt Whitman) discoveries in water depths of up to 305m in the Southern Gabon Basin. The development covers an area of 850.5km² within the Dussafu block, which is spread over more than 680,000 acres.
The block was declared commercial, and the exclusive exploitation authorisation (EEA) for Ruche was granted in July 2014.
The field development plan (FDP) was approved by the Direction Général de Hydrocarbures (DGH) in October 2014. The front end engineering design (FEED) studies are currently in progress, and the final investment decision (FID) is expected to be made in early 2015. Production is expected to start in the last quarter of 2016.
This is one of four well offshore drilling programmes to test a deepwater block of 2.6 million acres over the frontier Rovuma Basin offshore.
Harvest Dussafu, a wholly-owned subsidiary of Harvest Natural Resources holds 66.67% in the block and operates it. The company initially acquired a 50% interest in the field from Sasol Petroleum West Africa in December 2007 and a further 16.667% interest from Perenco in late 2008.
Panoro Energy holds 33.33% interest in the block, and had earlier acquired Premier Oil’s 25% share in the block in early 2008, as well as 8.33% of Perenco’s share in late 2008.
Contingent resources from the Ruche area are estimated at 13.2 million metric barrels of oil (mmbo) in 1C (low estimate), 33.4mmbo in 2C (best estimate) and 70.3mmbo in 3C (high estimate) categories.
The Ruche C field was discovered by Elf in 1981 after drilling the Moubenga-1 well, which flowed at an initial rate of up to 2,730 barrels of oil per day from the Dentale Formation. The Ruche D field was discovered by Amoco in 1995 after drilling the Walt Whitman-1 well, which encountered a 17m oil column in the Gamba sandstones.
The Dussafu Ruche Marine-1 (DRM-1) exploration well was dug up in April 2011 and completed in October the same year. The well, drilled by the Transocean Sedneth 701 semi-submersible drilling rig to a depth of 3,463m, encountered 19m of pay in a 28m oil column within the Gamba formation and 10m of pay in the Middle Dentale formation.
The well, appraised by a sidetrack well DRM-1ST1 located 1.2km south-west of DRM-1, encountered six metres of net pay in a 15m oil column in the Gamba. A further sidetrack well DRM-1ST2 located 890m north-west of DRM-1, encountered 12m of net pay in a 21m oil column.
The drilling of the Dussafu Tortue Marin-1 (DTM-1) exploration well within the Tortue prospect started in November 2012. Drilled to a vertical depth of 11,260ft, it encountered 42ft of pay in a 72ft oil column within the Gamba formation. The well also encountered 123ft of pay in stacked reservoirs within the Dentale formation.
A sidetrack well located more than 1,800ft from the DTM-1 well was further drilled to a depth of 11,385ft in the Dentale and 10,790ft true vertical depth (TVD) subsea to appraise the DTM-1 well. It encountered 65ft of oil pay in the primary Dentale reservoir. The wells at Tortue were drilled by the Saipem Scarabeo 3 semi-submersible drilling rig.
Several seismic acquisition programmes were performed on the block from 1994. 3D seismic data acquired earlier in 1994 was reprocessed and reinterpreted in 2008. The acquisition of 650km of 2D seismic data from the block was completed in October 2008.
An acquisition of 545km² of 3D seismic data was completed in November 2011 and processing was completed in July 2012. A 3D seismic acquisition programme by Polarcus, covering an outboard area of approximately 1,260km² started in July 2012 and culminated in late 2013. Another 3D seismic acquisition programme covering an area of 1,130km² was initiated in late 2013.
The development of the four oilfields within the Ruche area in Gabon envisages initial drilling activities at Ruche A, targeting the Gamba reservoir. It will be followed by Ruche B, targeting the Gamba and Dentale reservoirs, and the drilling of Ruche C and D drilling in later stages.
The wells will be tied back using subsea pipelines to Ruche A where the host platform, a floating production, storage and offloading vessel (FPSO) will also be located.
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