Online tool enables quick evaluation
of tieback options
The importance of subsea tiebacks in the deepwater Gulf of Mexico emerged and continues to grow motivated by three quite immutable trends. First, the average size of new discov- eries has fallen, reducing the economies of scale afforded by the early, very largest fields. Therefore, fewer new fields can
support stand-alone platforms.
Second, new discoveries are in increasingly deepwater. Despite
cost-saving improvements in technology, deeper water almost always
means higher development, production and transport costs.
Finally, a growing number of major deepwater platforms set over
the last 20 years have, or will have, rising excess capacity as the
production of their principal fields declines – it is cheaper to rent
capacity than to build it.
As a result, evaluating a new project, even
before bidding, increasingly requires examin-
ing tieback options. Here, we explain a tool and
methodology for that analysis. Its workflow
follows two stages: First, evaluate candidate des-
tination platforms by estimated spare capacity.
Second, determine a tieback path that minimizes
cost through a trade-off between distance and
slope, while recognizing and avoiding seafloor
obstacles. The tool is executed through a web
browser by GOM3, a specialized set of integrated
data and tools built on a geographic information
system (GIS) platform.
If a company’s new prospect is close enough
to its own platform, given sufficient capacity,
where to send the anticipated production is
simple. Much more often, a number of alternative destinations need analysis to develop a list
of good choices. Ultimately, in-depth engineering and commercial study will be required, but
listing candidate platforms’ estimated available
capacities is the first step.
We estimate a facility’s current excess capacity by subtracting its highest monthly production
in the preceding 12 months from its historical
maximum. Oil and gas are calculated separately.
This does not account for post-peak reduction
of capacity or commitments by an operator to
take production from other tieback projects but
serves reconnaissance purposes. We also note
whether or not the facility is currently producing
as some platforms are still officially “active” and
have high apparent idle capacity but may be in
the process of demobilization.
To illustrate the methodology, take as an example examining four
tieback scenarios from a single hypothetical origin at 26.906°N and
-94.218°W. This point is in 4,492 ft of water in block Alaminos Canyon
(AC) 079, covered by lease currently held by BHP. On entering the
origin location, the user is presented with a list of up to 10 of the nearest platforms within a maximum of 75 mi. They are sorted by distance
and show the block, water depth, operator, estimated current excess
capacities of oil and gas and current operating status. The operator
is included because that data may inform the choice of destinations.
In this example, three were chosen: from AC079 to the Hoover spar,
to the Gunnison spar and to the Nansen spar.
Of course, the shortest path between two points on a plane is a
straight line. However, the seafloor of the continental slope in the
Gulf of Mexico is far from being a plane. Some areas cannot be legally
traversed and others only at very high costs. Therefore, in searching
Earth Science Associates
John D. Grace
Number of deepwater (> 656 ft) wells in the Gulf of Mexico drilled by year and water depth between
1980 and the first half of 2017.
Distribution of estimated excess capacity for oil (in barrels of oil per day, BOPD) and gas (in thousands of cubic feet per day) on platforms in greater than 656 ft water depth in the Gulf of Mexico as
of Nov. 15, 2017.