American Oil and Gas Reporter - October 2017 - 79

SpecialReport: Gulf of Mexico Operations
The wells are connected through subsea well centers to a
new tension leg platform stationed in 3,350 feet of water at
Green Canyon Block 468. The TLP has designed daily topside
throughput capacities of 80,000 barrels of oil, 100,000 barrels
of water injection, 80 million cubic feet of gas lift, and 40
MMcf of produced gas export. The TLP was safely and successfully installed during the second quarter, and two rigs are
now on location performing drilling and completion operations
on the initial wells.
Figure 1 shows an overview of the Stampede subsea system.
The layout includes two, six-slot drilling and production centers
spaced about one mile apart that consist of 15,000-psi vertical
trees, production manifolds and gas lift distribution units. The
subsea centers are tied back to the TLP through piggable
flowlines. Both the production and injection wells are being
completed with multizone intelligent systems.
Hess Corporation is the operator of the Stampede Field and
holds a 25 percent working interest. Its co-owners in the project
are Union Oil Company of California (Chevron), Statoil and
Nexen Petroleum Offshore U.S.A., which each also have 25
percent working interests.
Dynamic Simulation
The Stampede project team identified dynamic simulation
as a validation tool during the early design phase. High-fidelity,
fully compositional models were developed for the subsea environment to simulate heat-transfer effects in well annuli and
better understand the interaction between production fluid and
gas lift injection for various startup cases. Once that model was
in place, the project team identified the need to continue using
topsides and subsea integrated simulation models to validate
additional phases in process design and engineering.
Consequently, a multipurpose dynamic simulator (MPDS)
was developed that proved to be crucial to engineering and operations. The scope of the MPDS grew as the project progressed,
and it was developed for application in many phases-from
concept selection and engineering studies, to control system
checkout, operator training, commissioning support and engineering design and support functions for possible future tiebacks.
The complexity of the Stampede development also required an
effective training system for field operators. Therefore, the
models developed during the engineering phase also were used
for operating procedure validation and training.
Using a simulator with dynamic full-facility components
(subsurface, subsea, hull and topsides) during each project
phase benefitted various disciplines, from reservoir and flow
assurance engineers to operations, automation and initial startup
teams. The integrated model provided tangible economic benefits,
leading to more informed design decisions throughout the
project's life cycle and minimizing the need for "workarounds."

Two dynamic simulation models were developed in parallel,
one focusing on the subsea system and the other on the topsides.
Each was built by different delivery teams to address specific
elements in Stampede's overall design.
The subsea model (wells, flowlines and risers) was built to
examine the dynamics of in-well gas lift and flow assurance. It
included component tracking and a detailed heat transfer model
of the wellbore to simulate the full effects of gas lift as effectively
as possible. In this model, the subsea part of the development
was modeled in high fidelity with a simplified view of the topsides.
The topsides model (topsides facilities and hull) was built to
provide a detailed model of the main process components
through the oil and gas train with a simplified view of the
subsea system. It was used to verify the configuration of topsides
equipment and the control system, allowing the design team to
simulate the interaction of equipment and controls at both local
and systemwide levels.
Example Applications
Examples of specific systems that benefitted from dynamic
simulation are the compression train and the oil export pumps.
In both cases, the MPDS was used to verify and fine-tune the
control system so that each system operated in a stable manner
through a range of simulated upsets, providing confidence in
the integrated control system.
It eventually became apparent that some of the simplifications
in the two models-the subsea model focused on flow assurance
and the topsides model focused on equipment design and control
strategy verification-did not fully show the dynamic nature of
the development. For instance, as lift gas is delivered in a well,
there is a recycle of gas through the two models that takes time
to build up and deplete if an upset occurs in either system.
Because the topsides system was simplified in the subsea model
FIGURE 1
Stampede Field Development

OCTOBER 2017 79

American Oil and Gas Reporter - October 2017

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