DEEPWATER CASE STUDIES
TEN extends Ghana’s,
Tullow’s deepwater credentials
Government, partner commitment drives project forward
Ghana’s second deepwater development has come onstream within budget, just over three years after the government sanctioned the project. The TEN project in the Deepwater Tano license covers three fields in water depths of 1,000- 2,000 m ( 3,281-6,562 ft), 20 km ( 12. 4 mi) west of the Jubilee
field. Operator Tullow Oil, in partnership with Anadarko, Kosmos
Energy, Ghanaian National Petroleum Corp. (GNPC), and PetroSA,
commissioned MODEC to convert the double-hulled VLCC
Centennial J into the 340-m ( 1,115-ft) long, 56-m (184-ft) wide FPSO Prof.
John Evans Atta Mills.
The FPSO, moored in 1,500 m ( 4,921 ft) of water, is designed to
process up to 80,000 b/d of oil and 180 MMcf/d of gas. It is connected via subsea manifolds, flexible flowlines and static/dynamic umbilicals to oil and gas production wells and water and gas injectors
– depending on performance and future plans, up to 24 development
wells may eventually be drilled. Tullow anticipates a productive
lifespan of 20 years.
Project manager Terry Hughes spoke to Of fshore about the various issues the partners dealt with along the way, including reservoir depletion mechanisms, managing engineering, lessons learned
from Jubilee, and local content.
Of fshore: This is Tullow’s first experience of overseeing development of a major deepwater project. How has the company approached this task?
Hughes: I joined Tullow in 2011 specifically for TEN, having previously worked with several upstream operating companies doing
major projects offshore and onshore around the world. I joined towards the end of the concept selection phase which had concluded
TEN was best developed using an FPSO and subsea infrastructure.
We then formed a team to complete the technical and engineering
requirements from all areas – subsurface, wells, subsea, facilities
etc – needed to make a well defined proposal to the field partners
to proceed with the development. That was done by early 2013 and
TEN completed its sanction and received government approvals in
May that year. The next step was to execute the sanctioned project
and the team was put in place to do this.
With Jubilee, Tullow concentrated on preparing for the operating phase after the major project phase was completed. The project
phase itself was executed by an integrated project team drawing expertise from all the partners, led by Kosmos Energy. Several Tullow
employees were part of this team, but Tullow’s focus was preparing
for operations, which meant assembling a significant group of people, mainly based in Ghana, to oversee field operations. Tullow took
all that experience and knowledge into the TEN Project which was a
significant step up in size and scale.
In the project’s early phase, our main partners, Anadarko, Kos-
mos and GNPC, had a lot of engagement with Tullow as they want-
ed to understand and provide input into our execution plan and the
building up of our team. As the project progressed on schedule and
on budget, I believe they became increasingly confident in our capa-
bilities, allowing them to step back a little.
Of fshore: The exploration campaign that led to the three TEN discoveries on the Deepwater Tano block took place during 2009-12.
What is your resultant understanding of these structures and their
Hughes: The acreage was covered by spec 3D seismic that had
been acquired in 2000. We call TEN ‘the field,’ although it actually
comprises various reservoirs in different formations – Tweneboa,
Enyenra, and Ntomme are various rock types. We have also procured
seismic outside the areas where oil and gas has been found in order to
correlate the data better, and to look at opportunities for future tie-ins.
Certainly, 3D seismic provides a lot more definition and helps to fine-
tune the bottomhole locations. And combining the 3D data with the
well results allowed us to optimize our development plan, including
the reservoir depletion mechanisms. We now know, for instance, that
one field features a gas cap and water drive rather than just being a
gas-drive field and we have modified our depletion plans in response.
As for our predictions on reservoir behavior, you might say we are
currently in the middle of the uncertainty range. But once we obtain
production history and see how the wells behave, we are hopeful the
volume of recoverable reserves will increase. So far all the wells have
come in on target, most with slightly better quality reservoirs than we
predicted. For several years we have installed pressure gauges in our
wells, enabling us to monitor the pressure pulses in the reservoirs
which gives our engineers valuable insight into how the reservoirs
will behave. It all looks good but we really need some production his-
tory to correlate our models and then we can update our predictions.
The main reserves, and consequently our focus for the early part
Location of the TEN fields offshore Ghana. (All images courtesy Tullow Oil)