Offshore Magazine - September 2016

48

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DEEPWATER CASE STUDIES

of the development, are in the Enyenra and Ntomme reservoirs. Most of TEN’s producing and injecting wells have been drilled on these structures which make up the bulk of the 300 MMboe we believe are recoverable. We are only developing one pocket of the reservoirs at Tweneboa, which is a gas field, and this is not due to start production until mid-2018. The depletion plan for the three fields differs: Tweneboa is via gas condensate blow down; Enyenra – pattern waterflood; and Ntomme – crestal gas injection and flank waterflood driven by reservoir geometry and fluids. Production rates per oil producer across the fields are variable, in the 10-15,000 b/d range. This was confirmed during short flowback tests when we were installing production tubing strings into the wells.

Of fshore: The 2009-12 campaign also led to discovery of the Okure, Oyo, Sapele and Wawa fields – why were these excluded from the current development?

Hughes: Our approved plan is to execute TEN as I have described which includes some pre-investment in the facilities to enable future developments and tie-ins to proceed efficiently. We are well placed now to evaluate options to extend the TEN plateau period or overall field life. We already have a team doing the early planning work and, when it’s complete, we will bring the options forward for our partners and the government of Ghana to consider.

Offshore: Various technical issues have
cropped up at Jubilee since production started
there, notably in the wells and more recently,
the bearings in the FPSO’s turret mooring sys-
tem. Were the partners looking to either rep-
licate or avoid certain experiences from that
project with TEN?

Hughes: We had an extensive lessons learned initiative in TEN which sought to replicate all the things that went well on Jubilee and avoid some of the issues seen after a few years of its production history. The timeframe between the discovery of the Jubilee field and first oil was incredibly short. The integrated project team did an excellent job bringing that field into production quickly, which benefited all parties, but inevitably they had less time to refine and optimize designs and execution plans. Taking this lesson on board, for TEN we expended extra effort on front-end work in order to ensure we had the right design and that the execution plan was sound. I believe we found the right balance between engineering, design and execution – and with firm project management and rigorous management of change culture, we were able to deliver on time and on budget. There are lots of stories of projects going wrong in the execution phase following repeated alterations to their scope.

Offshore: Government approval for the de-
velopment came in 2013, shortly after the con-
clusion of exploratory drilling. This seems ultra
fasttrack compared with other West African
deepwater projects – was this due to the gov-
ernment’s keenness to develop the country’s
oil and gas sector as quickly as possible.

Hughes: TEN was not actually planned and executed as a fasttrack development. Tullow does not think or act like a major oil company – we are a smaller organization with a more manageable portfolio. With less internal competition for resources, we are able to bring focus and get things done in a shorter period. Clearly, we had to conduct significant exploration and appraisal on a field of this complexity and we spent nearly $1 billion on E&A. With such a significant investment to confirm the size of the resource, we were highly motivated to bring the project for ward for sanction as quickly as possible and happily the government of Ghana was like-minded.

Offshore: Was one of the government’s conditions for sanctioning the project stepping up involvement of Ghanaian nationals, or would the partners have done this anyway?