Feature ArticlesSEA CON G3 Connector Provides Solution To Downhole Technology Gap
By Michael Mulcahy
Michael Mulcahy & Associates Inc.
Fiber optic tools offer an alternative method of measuring pressure, temperature, flow and wellbore/reservoir stresses. Optical communication systems enable significantly more bandwidth, higher data-transmission speed and much longer step-out distances (the distance from subsea installation to surface facilities) than traditional copper-based communication systems.
In the early 2000s, Houston, Texas-based Baker Hughes Inc. approached SEA CON® Brantner & Associates Inc. (El Cajon, California) looking for a multichannel, underwater-mateable electro-optical connector that could operate downhole in the company's global drilling operations. Baker particularly needed a connector robust enough to work with its proprietary real-time compaction imaging system, which delivers well and reservoir performance data when well conditions challenge the physical capabilities of electronic systems.
In addition, Baker needed a connector that would perform well for distributed temperature sensing, stress and strain monitoring, gravel screen monitoring and Bragg grating sensor applications.
In response to these needs, SEA CON developed the G3 connector, applying lessons learned through development, testing and manufacture of its successful HydraLight connector to create a product suitable for the downhole environment.
The G3 will initially be used to connect sensors in the downhole string, but will also be functional at the tubing hanger-to-Christmas tree interface.
Initial Product Design
In developing the new system for Baker, SEA CON found that some elements of its HydraLight connector could be tailored to Baker's new requirements.
The HydraLight is an eight-channel, underwater-mateable, oil-filled pressure-balanced connector, with each channel functioning as an independent or redundant data circuit. The device facilitates underwater connection of optical fibers at operating depths down to 7,000 meters (10,000 pounds per square inch), and its design life is 25 years. More than 1,200 HydraLight connectors are working in the oil and gas market today, and they have operated at a mean time between failures rate of better than 14 million hours.
In order to provide required functionality within highly restrictive dimensional constraints, the G3 connector had to assume a radical rectangular profile and fit into a one-inch-diameter space.
The HydraLight employs the patented 'joined-chamber' concept, which effectively seals the mating connectors together during the connector alignment (excluding sand, silt and debris) before joining the interior optical contacts within a clean oil-filled environment. Optics are never exposed to a contaminated environment, since mating occurs in a controlled environment.
Collaborating with Baker on this project enabled SEA CON to apply Baker's expertise in materials and finite element analysis modeling. This knowledge helped SEA CON meet the restricted space and high environmental specification requirements for downhole applications.
G3 Performance Requirements
Compared to the requirements for connectors whose working environment extends from the surface to the seabed, downhole connector products require advances in technology by an order of magnitude.
Downhole connectors must have high optical performance, including reduced insertion loss of better than 0.30 decibels and reduced back reflection of better than -50 decibels; the capability to withstand total combined operating pressure of 22,500 pounds per square inch; the ability to withstand temperatures up to 300° C; suitability for single-mode and multimode optical fiber; repeatable mate/demate cycling; and the ability to withstand exposure to downhole chemicals and solid-laden fluids (e.g., hydrocarbons, hydrates, drilling muds, hydraulic fluids and solvents, as well as other very harsh downhole materials, such as pipe dope) and their migration around and through the connector.
These requirements called for design elements including a hermetic interface to prevent migration of downhole fluids through control lines; a one-inch maximum connector diameter; optical fiber management, allowing for the efficient routing and storage of multiple fiber strings throughout the optical system; and a minimum number of surfaces that could collect and hold debris.
Not much larger than an average pen, the G3 can interconnect six optical channels in a harsh environment with greater optical performance than standard underwater mateable connectors.
Certain features of the HydraLight connector did not need to be changed for downhole operations. These included flexibility to accept single and multimode optical fibers, the joined-chamber mating environment and common sealing technology. But numerous aspects of the HydraLight did require changes.
First, the diameter of the connector was reduced from 3.5 inches to less than one inch, and the materials were upgraded to be capable of operating at simultaneously higher temperatures and higher pressures. Optical performance was improved in order to accommodate more optical connections in the total optical budget; fiber management was made linear with no room for loops in the space constraint; the header interface to control lines was changed from a low-pressure, low-temperature device to a high-pressure, high-temperature device; a new optical contact design and transport mechanism was designed; and alignment and tolerances were made to fit downhole constraints.
The greatest challenge was reducing the size of the assembly to dimensions that would fit into the available space while meeting more demanding performance specifications.
Operation at extreme temperatures with improved optical performance and ultimate reliability was the main design driver. Optical performance was further improved by utilizing angled physical contact optical terminations.
Both Baker and SEA CON conducted extensive laboratory and field testing of the G3 throughout 2009. To date, the G3 has passed prototype testing (mainly seal interaction); lab testing, including optics, forces, pressure testing and turbidity testing; and field testing for multiple mate cycles, turbidity, duration of operation and total system functional exercise. In addition, the G3 has successfully operated in several downhole land well installations.
The first offshore deployment is scheduled for the fall of 2010. This deployment will be the first permanent deployment in a production setting.
Although Baker's initial request was for an electro-optical G3, eventually Baker requested SEA CON to focus on an optical-only version for Baker's immediate needs, and an electrical version will be developed at a later date.
The G3 contains several unique, well-tested features that make it suitable for space-restricted downhole applications at elevated pressure and temperature conditions. Because this latest generation of SEA CON wet-mate optical connectors works well with a significant number of complementary products, clients can build complete underwater connectivity systems, including those in modular form (e.g., four G3s), taking advantage of the small form factor to gain circuit capacity.
Some products with which the G3 integrates well include dry-mate optical connectors (can be mated/demated on the surface but operate underwater and/or downhole), optical penetration systems, optical fiber tube conduits, optical fiber flexible conduits, optical splice boxes, fiber management systems and integrated optical cable, connector and sensor systems.
The G3 downhole mateable optical connecter is an enabling technology that will help allow oil and gas production to continue into the future.
New planned configurations, such as subsea/remotely operated vehicle versions, will increase demand for this new generation of connectors.
Michael Mulcahy is a former U.S. Navy officer and former Sea Technology magazine managing editor; he has written more than 100 articles for the magazine. His interests include undersea cables and connectors, marine engineering, naval architecture, commercial diving, remotely operated vehicle operations and ship salvage engineering. He is a graduate of the University of North Carolina at Chapel Hill.