separate flow regime prediction equations.
However all of the cited multiphase flow
studies are applicable to steady-state
flowing conditions. The development
of reduced-order mathematical models
predicting multiphase flow under transient
conditions is completely missing in the
open literature. There is an unexplored
coupling between the transient multiphase
flow and the heat transfer (heat flow from
the product through the pipeline and
into the ocean environment). The field of
modeling multiphase transient transport
is important to the subsea architecture
design and real-time optimization of
Subsea engineering presents many new challenges and opportunities for
engineers from any discipline. An excellent
tutorial reference source is [ 3]. Success in
subsea engineering directly addresses energy security while protecting the environment and marine life. n
The topside and subsea production systems are connected to each other
through an umbilical. The umbilical is a watertight conduit carrying electrical power, hydraulic power, chemical inhibitors, as well as other electrical
conductors and optical fibers for sensor interfacing, communications and
condition monitoring. The umbilical leaves the topside from the topside
umbilical termination assembly (TUTA) and plugs into the subsea distribution unit (SDU). The SDU distributes electrical and hydraulic power, and
receives sensor and other communications all through flying leads (cables
and flow lines connecting one subsea subsystem to another).
ENGINEERING CHALLENGES FACE SUBSEA SYSTEM DESIGN
Designing subsea systems for 30 year long controllability, safety, main- tenance, and real-time optimization are critical issues and present an
open-ended problem. Below is a summary of the two primary challenges
associated with the design of the subsea architecture. Topics not reviewed
include condition and performance monitoring, materials and corrosion,
Safety is absolutely a primary focus on any subsea production system
design. There must be multiple independent safety paths in place to isolate
a producing well. The most common subsea safety system is located within
the well. It is called the surface control subsurface safety valve and requires
hydraulic pressure to keep the reservoir flowing. When hydraulic power is
lost, the valve closes thus isolating the well. The subsea XTree can also be
used to isolate the well by closing the choke. Downstream of the manifold is
a high integrity pressure protection system (HIPPS). This system automatically closes a gate valve when the pressure in the pipeline is too high.
The presence of multiphase flow in a subsea production system
complicates system design and operation. There are multiple flow regimes
that can exist for multiphase flow in horizontal pipelines [ 5]. Pioneering
work performed at the University of Houston provided mathematical
relationships to predict the flow regime given gas and liquid velocities,
including dispersed bubble flow, elongated bubble flow, slug flow and
stratified flow to name a few. Vertical multiphase flow has completely
ABOUT THE AUTHOR REFERENCES
Dr. Matthew Franchek is the founding director of
the University of Houston Subsea Engineering Program.
He received his Ph. D. in mechanical engineering from
Texas A&M University in 1991 and started his career at
Purdue University as an assistant professor in mechani-
cal engineering. He was promoted to full professor in
2001. While at Purdue, he initiated and led two industry
supported interdisciplinary research programs: in automotive research and
electro-hydraulic research. From 2002 to 2009 he served as chair of mechanical engineering at UH while simultaneously initiating the UH biomedical
engineering undergraduate program. After his term as Department Chair, Dr.
Franchek worked with Houston area companies to create the nation's first
subsea engineering program. His expertise is in model-based methods for
diagnostics and control of aerospace, automotive, biomedical and energy systems. His current research program focuses on multiphase pipeline flow, artificial lift, blowout preventers and electrical power distribution. He has authored
over seventy archival publications, and over 100 conference publications.
1 Dragani, J., and Kotenev, M., “Deepwater Develop-
ment: What Past Performance Says About the Future,”
The Way Ahead, Vol. 9, No. 1, pp. 8-10, 2013.
2 Cleveland, C.J., Editor, Deep Water: The Gulf Oil
Disaster and the Future of Offshore Drilling, National
Commission to the BP Deepwater Horizon Oil Spill
and Offshore Drilling, 2011.
3 Bai, Y., and Bai, Q., Subsea Engineering Handbook,
Elsevier Incorporated, Kidlington, Oxford, 2010.
4 Bai, Y., and Bai, Q., Subsea Pipelines and Risers,
Elsevier Incorporated, Kidlington, Oxford, 2005.
5 Taitel, Y., and Dukler, A.E., “A Model for Predicting
Flow Regime Transitions in Horizontal and Near
Horizontal Gas-Liquid Flow”, AIChe Journal, 22,
pp. 47, (1976).