high quality, and most importantly being able to satisfy the
customers’ needs. Higher-order 3-D simulations allow the
design engineer to thoroughly investigate the design’s characteristics in virtual space, without expensive pre-testing
of prototypes, to verify the concept’s performance against
specifications set by the customer.
Such tools as ANSYS Mechanical and Abaqus for
structural analyses, and Fluent, CFX, and STAR CMM+
for computational fluid dynamics investigations are used
significantly in the oil and gas industry. Other commercial
software tools, such as RIFLEX and ZENRISER, are employed for static and dynamic analysis of slender marine
structures. The dynamic behavior of offshore flexible or
rigid riser or pipe systems is subject to hydrodynamic
loading and vessel motion that need to be modeled to
ensure reliable operation. They represent simulation technology used for riser analysis suitable for flexible, metallic
or steel catenary riser applications.
In offshore applications, subsea trees and manifolds
The results of the steady state and transient cool-down
are employed for production purposes. Due to the harsh
corrosive environment and constant cold condition, which
approaches near freezing temperature, thermal insulation
is used to ensure the reliable and cost efficient manage-
ment of flow of hydrocarbons from the reservoir to top-side
floating production vessels or via subsea piping systems to
onshore processing facilities. The objective many times is to
determine whether or not the thermal insulation system on
a subsea tree and/or manifold is capable of maintaining the
produced fluid temperature above hydrate formation tem-
perature (HFT) for a specified period of time (e.g., greater
than 12 hours) after shutting down the well. Higher-order
fidelity, 3-D, transient computational fluid dynamic model-
ing is used to simulate such operating requirements. Figure
2 shows the meshing scheme used to model such a system
to guarantee convergence in a timely manner.
time of a multiphase flow is shown by Figures 3 and 4, re-
spectively, where red indicates hot and blue indicates cooler
A “tree” is an assembly of valves, spools, and fittings
used for an oil well, gas well, condensate well and other
types of wells. The primary function of a tree is to control
the flow, usually oil or gas, out of the well. A tree may also
be used to control the injection of gas or water into a nonproducing well in order to enhance production rates of oil
from other wells.
The modeling of the actual physics (using CFD) of the
fluid provides a more realistic insight of the actual thermal
performance than traditional methods of determining cool-down times using finite element techniques. This is further
magnified once the analysis complexity is increased by the
introduction of a multiphase fluid in the flow stream instead
of a single fluid (e.g., gas or liquid).
A subsea manifold is a large metal piece of equipment,
made up of pipes and valves and designed to transfer oil /
gas from wellheads into a pipeline. Manifolds are usually mounted on a template and often have a protective
structure covering them. Manifolds vary greatly in size
and shape, though these can be huge structures reaching
heights of 30 meters ( 90 feet).
Figure 5 shows analysis results for a subsea manifold for
a transient cool-down simulation.
The thermal design challenge becomes the determination of thermal insulation thickness and its placement to
minimize thermal losses and thus prevent hydrate formation. Hydrates are ice-like crystals that form with natural
gas and water and at combination of low temperatures and
high pressures. Thermal insulation on subsea trees and
manifolds is always required to prevent the rapid decrease
FIGURE 2 Meshing used for the tree - CFD Modeling: 4. 7 million
polyhedral cells (6-layer fluid boundary inflation).
FIGURE 3 Steady-State temperatures
in the subsea production tree during
FIGURE 4 Transient temperatures
after 8 hours of cool down
time in the tree.
FIGURE 5 Transient temperatures
after 8 hours of cool down
time in the manifold.