The document describes the ATP Titan, the latest design for deepwater production units called the MinDOC 3. Some key points: - The ATP Titan was installed in the Gulf of Mexico's Mirage Field, establishing the MinDOC 3 design. - The MinDOC 3 was chosen for its design advantages over competing concepts like stability and response to waves. It provides higher load capacity than semisubmersibles or spars. - The MinDOC design was originally envisioned in 1997 and has undergone years of iterations and redesigns to arrive at the MinDOC 3, which can be transported by existing vessels worldwide.

1. B
BennettNaval Architecture and Consulting Services
Volume 03 Issue 01-February 2010
Reprinted from

2. Jose Vazquez,
Bennett & Associates, USA,
describes an innovative
design for deepwater
production units.
cover
story

3. A first for
deepwater
units
T
he ATP Titan has been installed in the
Central Gulf of Mexico, establishing the
MinDOC®
3 as the latest design for deepwater
production units.
The hull has been taken from the graving dock
at Gulf Marine Fabricators in Ingleside, Texas, and
towed to the Gulf of Mexico’s Mirage Field
(Mississippi Canyon 941), part of ATP Oil & Gas’
Telemark Hub. Mooring has been completed and
topsides have been installed.
ATP decided to develop the Telemark Hub
with the MinDOC 3 due to the unavailability
of infrastructure in the vicinity and its design
advantages over competing concepts. According
to T. Paul Bulmahn, Chairman and CEO of
ATP, ‘The design looks like a semisubmersible
but behaves like a spar in terms of stability
and dynamic response to waves. It provides a
higher load capacity and enhances stability over
previously designed semisubmersibles or spars.’
After fully producing ATP’s Mirage and Morgus
(Mississippi Canyon 942) reserves, the ATP Titan
may be redeployed to ATP’s development at
Atwater Valley Block 63, the second phase of the
Telemark Hub.
Image: Upending of the ATP Titan is almost complete at the Gulf of Mexico’s
Mirage Field (Mississippi Canyon 941), part of ATP Oil & Gas’ Telemark Hub.

4. MinDOC history
The image of a multi-column hull designed for deep water, sailing
out of an American fabrication yard, was envisioned in 1997 by
offshore oil pioneer Alden ‘Doc’ Laborde, Chairman and Founder of
Gulf Island Fabrication. When Bennett & Associates joined to be the
naval architects for the design, William T. Bennett convinced
the group of the merits of a three column design rather than a
multi-columned design. The merits lie in the simplicity of fabrication
and operation as well as excellent motions required for dry tree
applications.
Laborde, whose list of inventions includes the first transportable
semisubmersible rig and the first supply boat, was seeking a
deepwater floating production unit that could be built along the
Gulf of Mexico to bolster the sagging markets for fixed platforms. In
an effort to attract some of the business that was going to foreign
builders for deep water, he put together a consortium of several
Louisiana offshore design companies to develop and market a
floating production unit that could be built in the USA. This team
worked together for three years developing the original MinDOC and
the second generation MinDOC (MinDOC 2).
The first two designs were competitors to the classic spar
concepts in that they exhibited low motions and had deep
drafts. However, the MinDOCs did not rely on permanent (high
density) ballast to enhance their pendulum stability. MinDOC 2
was developed in the year 2000 for a specific Gulf of Mexico
application. It was too long to be easily dry towed, which proved
to be a disadvantage in case the hull had to be built overseas.
This precipitated a design spiral to develop MinDOC 3, which
would be capable of being transported on several of the existing
heavy lift vessels, and was therefore suitable for worldwide
construction.
Bennett & Associates undertook years of iterations in designing,
testing and redesigning MinDOC. The company eventually
purchased the intellectual property rights to all of the MinDOC
designs from the original members of the consortium.
Unique features
The MinDOC designs are unique in that they are neither spars
nor semisubmersibles, but possess many of the best features
of both other designs. From its inception, the original MinDOC
introduced several new concepts for deep draft production units.
The subdivision of the hull featured a centre trunk that permitted
access to any one compartment without compromising the
watertight integrity of adjacent compartments. The access trunk
also housed all the piping for the simplified ballast and bilge
systems, providing accessibility to all valves.
The ballast system was simplified compared with typical
semisubmersible and spar designs and featured an over-the-top,
pump-in and pump-out system that eliminated the possibility of
transferring ballast from one column to another. Additionally, the
Figure 1. ATP Titan was removed from the graving dock at Gulf Marine Fabricators in Ingleside, Texas.
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5. design was configured to prevent accidental transfer of ballast water
from a lower compartment into a higher compartment, should a
valve either malfunction or inadvertently be left open. All MinDOC
designs include no sea chests or other hull penetrations below the
operational waterline.
Post-Katrina standards
Hurricanes Katrina and Rita made the offshore industry
increasingly concerned about the design criteria for new
Gulf of Mexico production units possibly experiencing hurricane
force conditions. The company said the MinDOC 3 had been
designed to more strenuous environmental criteria than other
deepwater production designs and was more easily adapted for
the Post-Katrina 100 year return environment. The air gap of all
MinDOC designs has been constant from the start and provides
adequate wave clearance for the new API criteria.
According to the company, MinDOC is the first structure for
the Gulf of Mexico designed to the new criteria following Katrina,
the first structure for the central region of the Gulf of Mexico,
which is the most hostile area, and therefore it’s the first deepwater
production structure that has been designed specifically to move
from site to site.
The first MinDOC had been designed for 100 knot winds
and had an air gap of 70 ft. Having started from those design
parameters, it was easier for Bennett engineers to adapt the
MinDOC 3 to meet post-Katrina design conditions.
Classification by ABS
Upon initial evaluation of the design by the classification society
ABS, it was evident that MinDOC did not directly fit any specific
classification rules. ABS had to either consider it as a unique
concept or decide which rules could best meet classification
objectives. The decision was made that since the stability of the
Figure 2. ATP Titan was towed from Ingleside, Texas, to the Gulf of Mexico.
Figure 3. MinDOC 3 is a patented, deep draft floating production
system designed by Bennett & Associates for support of dry tree
completions in deepwater environments.
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6. unit was achieved with high density ballast and the typical marine
systems were both more spar-like concepts, it would be best to
class the MinDOC as a spar.
Through early and constant co-operation between
Bennett & Associates and ABS, a thorough understanding of the
features, strengths and weaknesses of the MinDOC and of the rules
and recommendations was shared. Such an approach helped both
the designer and the classification society to more fully understand
the innovative technology, concepts and functionalities that were
being considered, and to identify how these approaches could be
harmonised with the applicable regulatory and industry standards
while maintaining the feasibility of the project.
Ultimately, ABS was able to determine the applicable
classification requirements in time to enable the designers to
proceed with the development of the ATP Titan project and not
delay the project construction schedule.
Stability
The ATP Titan features both the stability of a spar (pendulum
stability) and that of a semisubmersible (water plane stability); a
combination that produces high payload capacity and motion
characteristics. It is by applying the capabilities of both types of
stability that MinDOC achieves a high degree of flexibility and
adaptability with respect to loads and weight growth.
The pendulum stability is achieved by the use of high density
ballast in the lower raft compartments. Portions of the MinDOC
(lower raft, lower columns and upper pontoons) are free flooding to
reduce the scantlings of these members in areas not required for
buoyancy to support the hull, topsides and live loads. Buoyancy of
the unit is primarily obtained from the upper columns.
From a dynamic response perspective, the MinDOC 3 also
behaves more like a spar than a semisubmersible, with very good
heave and pitch motions, as needed to support dry trees, top
tensioned risers (TTRs) and steel catenary risers (SCRs). The
ATP Titan MinDOC 3 is fitted with a drilling unit, making it capable
of fully drilling its own wells. This feature provides economical
advantages by eliminating the need for pre-drilling wells and working
over the vertical access wells. The ATP Titan is also fitted with a
subsea intervention device (SID) that can close to secure the wells
at any time during the drilling operation and allows the use of a
pressurised drilling riser with a surface blowout preventer.
It also features a riser support structure built into the hull rather
than the topsides, where riser tensioners had typically been located.
This allows the drill deck elevation to be significantly reduced and
provides added protection for the risers at the waterline.
Some of the column compartments have been designed for
the storage of consumable liquids such as drill water, diesel oil,
base oil and drilling mud. One of the compartments was designed
to accept methanol storage while in service. Other compartments
house equipment and at one time had space for an auxiliary
generator.
Compartments in the upper pontoons and lower columns
adjacent to the critical connections were designed to permit them
to be dewatered, providing access for inspection in these areas
as required. This would also allow for repairs in the dry should the
requirement ever present itself.
Titan geometry
The MinDOC 3 adapted for ATP Titan consists of three 52 ft
diameter buoyant upper columns and three smaller 20 ft diameter
non-buoyant lower columns held in spatial relationship by upper
pontoons and a lower raft. The spacing between the centrelines of
each column is 150 ft. The hull is 485 ft high.
The upper columns are outfitted with helical strakes to reduce
vortex shedding. The ‘partial’ strakes provide overall coverage, but
only partial coverage of any individual column. The exterior portions
of the columns have no strakes, which improves constructability and
operability. Some other MinDOC bare hull designs have exhibited no
VIM in model testing, presumably due to the difference in upper and
lower column diameters and other hull geometry features.
Topsides
The hull can accommodate traditional rectangular topsides, but the
company has designed modular, triangular topsides, which reduce
structural weight and add precious deck area. The ATP Titan has
unique T-shaped topsides composed of a process module and a
utility module. The topsides have a design capacity of 25 000 bpd
and 50 million ft3
/d.
Scalable design
The MinDOC is a highly scalable design and can accommodate
either small or large topside loads and configurations. Several
versions have been developed that range in topside loads of
3000 - 35 000 t and water depths of 1500 ft to near 10 000 ft.
It can be designed for surface trees, a hub to tieback subsea
wells or a combination of both, as is true for the ATP Titan. Versions
for topside integration at a quay side have been designed to
eliminate the need for offshore integration, heavy lift vessels and
permit installation in remote areas.
Although the three column version is preferred for several
reasons pertaining to efficiency, four column versions have also
been designed. The three column version offers added simplicity for
operation by production crews and the loads applied to the critical
connections are statically balanced and minimised if the unit is kept
on even keel.
Multiple columns may produce uneven loading of the
connections due to different ballast conditions. As the expensive
part of the MinDOC construction is at the nodes, the three column
version presents important cost savings. However, since the
buoyancy comes primarily from the columns, the four column
designs offer the potential for higher topside loads.
ATP plans to reuse the ATP Titan multiple times throughout its
lifespan, moving it from project to project in the deepwater Gulf. O T
Figure 4. With ballasting complete, the first MinDOC 3, the
ATP Titan, awaits mooring and installation of topsides.
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