Last updated: 20 Mar 2013
In March 2009, the Tweneboa-1 exploration well, in the Deep Water Tano licence, 25 km from Jubilee, discovered a highly pressured light hydrocarbon accumulation.
The well encountered 21 metres of net pay on the edge of a giant 200 sq km fan system related to the Jubilee play. Intriguingly, the well also encountered a four metre over-pressured oil-bearing sand and an over-pressured zone at total depth.
Tullow planned to carry out appraisal drilling to test core areas of the structure where thicker reservoir sections are mapped. The second well, Tweneboa-2 began drilling towards the end of 2009. In January 2010, Tullow announced that the well had encountered two separate hydrocarbon columns containing oil and gas-condensate legs. In total, 32 metres of net pay were encountered.
In July 2010, the Owo-1 exploration well encountered 53m of light oil pay. This was followed by a sidetrack well which encountered an additional 16 metres of net oil pay in the lower part of the same channel system. Pressure data indicates that this oil pay is in communication with the reservoirs penetrated in the Owo-1 well and confirms at least 69 metres of total net oil pay in a substantial gross oil column of 200 metres. Drilling further ahead, two gas/gas-condensate legs were also encountered totalling a further 19 metres of net pay.
During 2011, significant progress was made in the programme of appraisal drilling and flow testing of the Tweneboa, Enyenra and Ntomme fields, collectively known as TEN. Tullow anticipates developing the three accumulations in an integrated subsea cluster development scheme using a single FPSO.
2011 accelerated appraisal
The appraisal programme commenced in January 2011 with the drilling of the Tweneboa-3 well comprising two deviated exploratory boreholes drilled into the Ntomme prospect which was proven to be a material and separate gas-condensate accumulation.
Further appraisal drilling on the Enyenra field has continued during 2011 including the re-drill of the Owo-1 discovery well in December 2011, to allow testing and coring. To determine the level of reservoir connectivity and well deliverability, the well was flow tested. The lower channel was tested at a rate of approximately 10,000 bopd, and a commingled rate for the two upper channels was approximately 12,000 bopd. The pressure response will be monitored by pressure gauges deployed in the Enyenra-2A and Enyenra-3A wells, located to the south and north respectively.
Continued appraisal success in 2012
In the first half of 2012, the appraisal drilling and well testing for the TEN project made good progress with three wells drilled in support of the Plan of Development (PoD). The Owo-1RA well was drilled and successfully tested in February 2012 at combined rates of 20,000 bopd. Enyenra-4A was drilled in March 2012, intersecting 32 metres of oil pay. Water injection tests on this down-dip well were carried out in April 2012 with results proving that the Enyenra channel sands are suitable for water injection to support oil production.
The Ntomme-2A well was drilled in May 2012 and found oil down dip of the Tweneboa-3ST gas discovery (the Ntomme discovery well). The well was production tested at combined flow rates of around 20,000 bopd confirming excellent quality reservoir. As part of the overall appraisal programme pressure gauges were installed in a number of the wells and gauge readings have confirmed reservoir continuity across each of the individual Tweneboa, Enyenra and Ntomme fields.
The data from the appraisal activity in the first half of 2012 has enabled the subsurface models for the TEN fields to be updated and the combined resources range is 200 to 600 mmboe with most likely resources of 360 mmboe of which 70% is oil.
Plan of Development
In the second half of 2012, the Tweneboa, Enyenra and Ntomme (TEN) project made good progress and Tullow and partners submitted the Plan of Development to the Minister of Energy in early November 2012. The development is being designed with sufficient flexibility to allow both TEN resources and nearby discoveries to be tied into an FPSO. Following the Wawa discovery on the Deepwater Tano block in July 2012, an appraisal programme is now being evaluated. The Okure exploration well to the south of TEN was unsuccessful in discovering hydrocarbons.