DSC manufactured the 15 mm diameter rod with fibre optic core, which functions as a sensor, gathering valuable real-time insight on well behaviour unattainable using conventional methods.
Improving oil recovery factors
In order to make informed decisions, oil drilling and completions teams need detailed information on fluid flow in and around the borehole during production or injection. Such data is usually collected using production logging tools, but this method is operationally challenging and provides limited, time- and location-specific information. Ziebel’s proprietary technology, the distributed fibre optic (DFO)-based Z-System, is free of many of the constraints that limit conventional well logging effectiveness, offering improved understanding of well and reservoir behaviour.
At the heart of Ziebel’s Z-System is the DSC-manufactured 6.2 km long, 15 mm diameter carbon fibre rod (the Z-Rod), which delivers multiple fibre optic cables securely into the hostile downhole environment. Typically, the rod is deployed into a producing or injecting well for 48 hours where the fibre optic sensors measure temperature and acoustic vibrations along its length. This enables a variety of applications – including flow allocation, fluid movement visualization, leak detection and stimulation fluid monitoring – which are extremely valuable for optimal well and reservoir management.
This composite-based sensing system offers further advantages. The carbon rod enables horizontal well access, since the lightweight, stiff composite rod can be ‘pushed’ from the surface into the horizontal sections frequently employed in today’s wells, which is not possible with conventional tools run on a wireline unless an electrical well tractor is employed. In addition, the small-diameter carbon rod can access wells with restricted internal diameters and difficult geometry where other tools will not pass, it has minimal choking effect on the well, and unlike metals, it is inert to the majority of hazardous and corrosive substances found in the downhole environment.
A robust manufacturing process
Ziebel contacted US-based carbon fibre pultrusion specialist DSC in 2006 to develop and manufacture the robust composite rod required to launch its fibre optic intervention technology in the oil sector.
To ensure the required combination of strength, stiffness and corrosion resistance necessary for this application, DSC selected one of its proprietary, tough epoxy resins and a specific carbon fibre selected through extensive testing to maximise mechanical performance. This resin places particularly challenging demands on the pultrusion process, since it requires a very slow cure in order to attain its optimal properties. This means that to produce each 6.2 km long rod, the pultrusion line must run continuously, without fault, for more than 3 weeks.
“Because of the high cost of both the carbon fibre and the fibre optics, the process risk is very high,” David Lewis, DSC’s Director of Technology & Business Development explains. “We’ve therefore performed extensive work to develop a pultrusion process that is extremely robust and foolproof, and exceptional process controls are in place to ensure that there are no failures.”
Ziebel and DSC have worked together to optimise a spooling technology to facilitate the handling and transport of long lengths of pultruded rod. This enables the stiff carbon fibre rod to be wound onto reels that are small enough in diameter to allow shipping from DSC’s production facilities in Erlanger, Kentucky, to Europe and the Middle East as well as within the US. An NDT process is used to monitor rod quality since the product is continuous and cannot be cut for inspection.
Ziebel is committed to expanding its product portfolio through innovations in its current Z-Rod product, as well as other products for similar applications that will take advantage of its fibre optic sensing and data analysis capabilities.
“We have a great deal of trust and confidence in our partners at DSC that will enable us to continue pushing the boundaries for carbon composites in the hostile downhole environments of oil and gas wells,” says Neil Gardner, Ziebel’s Vice President of Technology. “Our next generation of Z-Rod will take us to operating temperatures of 350°F (177°C), opening up additional wells for our services.”
Ziebel and DSC have entered an exclusive agreement to develop and produce advanced fibre optic/composite downhole sensor rods based on Ziebel technology.
Companies: Exel Composites