48
AUGUST 2003
The full-length paper provides a brief
overview of fiber-optic systems proposed
for use in intelligent wells, reports on the
development and application of a high-
pressure/high-temperature (HP/HT) con-
nector, and discusses the optical and
mechanical performance and qualifica-
tion requirements for this application.
Introduction
One of the most important areas of offshore
oil and gas R&D in recent years has been
the ongoing development of improved
reservoir- and production-monitoring tech-
nology. The continuing development of
intelligent-well monitoring technology and
intelligent-well control has the potential to
increase recoverable hydrocarbons by 5 to
15%. One of the primary techniques for
implementation of intelligent-well technol-
ogy is use of optical fiber sensors to provide
high-quality data on downhole conditions
continuously and in real time with HP/HT
compatibility. The suite of sensor technolo-
gies includes fiber-optic distributed temper-
ature sensing (DTS), in-fiber point-source
sensors typically of the Bragg-grating type,
and passive mechanical point-source sen-
sors that are read optically through an
attached optical fiber.
These sensor technologies require a
means of passing the fiber out of the well.
For land-based systems, this is easily
achieved through fiber packer systems.
Subsea systems require that a fiber-optic,
wet-mate connection be built into the
Christmas tree before installation and be
capable of termination to the downhole,
fiber-optic gauge cable. With fiber and fiber
sensors in the well, there also is a need for
reliable wet-mate and dry-mate fiber-optic
connectors in the well to facilitate normal
installation and workover practices.
History
The first one-circuit high-performance fiber-
optic connector qualified for subsea applica-
tion was developed for the U.S. Navy in
1983. A direct face-to-face contact between
two fibers is necessary to provide the optical
performance requirements for most multi-
connector systems. The first optical connec-
tor maintained a clean, oil-filled, pressure-
balanced environment around the bare fiber
contact in both the plug and receptacle con-
nectors and caused the mate to occur in a
clean environment. In this system, the bare
fiber was passed through the dual-seal sys-
tem, and mating alignment was controlled
inside the receptacle by use of three cylindri-
cal roller bearings.
Connection System Development
Development began in 1999 of a small fiber-
optic connector suitable for the tree-to-tub-
ing hanger interface and for downhole
applications. The two primary prerequisites
of a connection system for these applica-
tions are small size, typically less than
1
1
/
2
in., and environmental compliance.
A review of the space envelope and envi-
ronmental requirements for Christmas tree
and downhole equipment confirmed that
modification of the successful subsea wet-
mate rolling-seal connector would not be
viable, but that many of the proven compo-
nents including the optical stem assemblies
and fiber-alignment system would be suit-
able starting points for the new connector.
The main new component needed for the
small connector was a radically different
seal system that would isolate the plug and
receptacle stem assemblies in a clean, pres-
sure-balanced, oil-filled environment. At the
same time, the seal must exclude sand, silt,
and seawater, and open during mating to
allow passage of the optical plug stem
through both plug and receptacle seals.
The connector design builds heavily on
the knowledge base gained from 6 years of
development and installation experience
with wet-mate hybrid connectors and
implements many of the proven design and
performance features from this subsea fiber-
optic connector product range. The wet-
mate, fiber-optic connector is just one facet
of the equipment needed to pass fiber
through a vertical or horizontal tree system.
Typically, 15,000-psi fiber penetrator sys-
tems are needed at multiple locations
through the Christmas tree and tubing
hanger assembly. A compliant pressure-bal-
anced mounting system that provides axial
and radial float is needed at the Christmas
tree/tubing hanger interface. A means of
protecting the fiber through the valve block
and tubing hanger is required, and a dry-
mate connector is needed at the base of the
tubing hanger to connect to the optical fiber
in the gauge cable. The dry-mate connector
is an existing and field-proved design.The
connection system was designed to be com-
patible with vertical and horizontal
Christmas tree systems.
First Application
The first application for the connection sys-
tem will be for BP on the Atlantis project in
the deepwater Gulf of Mexico. Initial design
of the two-circuit connector was reviewed
for compatibility with a remotely operated
vehicle (ROV) installation that offers many
advantages for horizontal Christmas tree
systems. This installation system provides a
wet- and dry-mate connection for the run-
ning tool that will allow direct fiber com-
munication with the sensors from a diag-
nostic system on the installation vessel and
with optical fibers in the riser. The system
design uses an ROV-installed vertical wet-
mate connection system where the ROV
performs a vertical stab through the tree cap
to mate the floating receptacle onto the tub-
ing-hanger-mounted plug.
The fiber-optic sensor control system res-
ident in either a 14.7-psi control pod or on
the platform will terminate subsea with a
wet-mate, fiber-optic bulkhead connector. A
fiber-optic jumper assembly that terminates
This article, written by Assistant
Technology Editor Karen Bybee, con-
tains highlights of paper OTC 15323,
The Development and Application of
HT/HP Fiber-Optic Connectors For Use
on Subsea Intelligent Wells, by Perry
Wright, Stewart Barlow, and Anton
Brees, Ocean Design Inc., prepared for
the 2003 Offshore Technology Con-
ference, Houston, 58 May.
Copyright 2003 Offshore Technology
Conference. Reproduced by permission.
The paper has not been peer reviewed.
D eve l o p m e n t o f H P / H T F i b e r- O p t i c
C o n n e c t o r s fo r S u b s e a I n t e l l i g e n t We l l s
O f f s h o r e C o m p l e t i o n s AUGUST 2003
49
with an ROV vertical wet-mate stab connec-
tor will connect the control module or
umbilical termination to the Christmas tree.
The vertical stab connector comprises an
ROV handle and latching mechanism, the
compliant pressure-balanced stinger that
provides axial and radial compliance, and
the wet-mate receptacle connector. A guide
funnel that provides the ROV latching pro-
file and primary rotational and axial align-
ment is mounted on the tree cap.
The wet-mate plug connector, the
14.7-psi fiber-optic protective tubing, and
the dry-mate receptacle connector are
assembled and tested as a single unit. The
unit is installed through the tubing hanger
and provides full dual-barrier metal sealing
for the 10,000-psi operating pressure at the
top and bottom surfaces of the tubing hang-
er. The plug connector seals to the tubing
hanger by means of metal and elastomeric
seals. The dry-mate connector at the lower
face of the tubing hanger is sealed with a
seal pack that uses metal and elastomeric
seals. The dry-mate plug connector is field
terminated to the fiber-optic gauge cable by
one of two installation methods. Fig. 1
shows connector dimensions.
Specification. The connection system
being qualified is compatible with the
Atlantis field requirements. The preferred
elastomer for the face seals and compen-
sators has been tested for compatibility with
seawater, silicon oil, glycol, calcium bro-
mide, calcium chloride, and other chemicals
commonly encountered in the oil and gas
industry. Performance specifications for the
connection system include the following.
0.5 dB contact for single-mode or mul-
timode fiber system.

30 dB return loss.
10,000-psi operating pressure.
15,000-psi test pressure.
266�F operating temperature with a
40�F installation temperature.
15 mate cycles from installation.
20-year life expectancy.
Zero to 0.2-in. axial alignment.
0.45-in. radial misalignment.
1.0� rotation.
0.5� misalignment from the mounting
point.
Future System Development
Vertical Christmas Trees. A similar wet-
mate connection system would be needed
for a vertical Christmas tree system. The
main difference from the horizontal system
would be that the ROV installed stinger
assembly would be modified to be mount-
ed into the lower face of the valve block
with a fiber-optic pressure penetrator and
would reside within the spool piece
attached to the lower face of the valve
block. The fiber would be run through the
valve block to a bulkhead-mounted pene-
trator and fiber management system within
an American Petroleum Inst. standard
flange mounted on the outside of the
Christmas tree, from which a jumper
assembly would take the fiber to the sensor
control pod or umbilical termination.
Horizontal Christmas Trees. For a hori-
zontal tree using a horizontal connection
system, the wet-mate plug connector would
be mounted horizontally in the tubing-
hanger wall. The wet-mate receptacle would
be mounted by the compliant stinger as a
part of the penetrator assembly on the out-
side of the Christmas tree and actuated by
ROV or through a hydraulic or electrical
assembly that causes the penetrator