This study presents the evolution of downhole fiber optics to a new hybrid electro-optical cable for coiled tubing (CT) applications. The optical fibers enable optical communication and distributed measurements such as distributed temperature and acoustic sensing. The electrical layer delivers continuous surface power to downhole tools, eliminating typical battery limitations such as temperature, operating time, and safety concerns. The electrical layer also enables cable telemetry operation of wireline tools.
The hybrid cable is composed of several layers: an inner tube protecting the optical fibers, a layer of low-DC-resistance conductors to deliver high voltage downhole, an insulator, and an outer tube that is exposed to the fluids in the CT pipe. This complex cable is packaged with an outer diameter of only 1/8 in to maintain maximum flow rates achievable through the pipe. Surface and downhole equipment used with the cable are designed to accommodate electro-optical terminations separating the conductors and optical lines.
The cable has been manufactured, tested, and installed in CT pipes. The surface and downhole equipment has been designed and certified to operate in both land and offshore environments and tested with multiple families of tools: well intervention tools instrumented with pressure, temperature, depth control, and load sensors; wireline tools, including pulsed neutron generator and flow profiling tools; a multilateral re-entry tool; and an electrically actuated multiple-set retrievable plug.
Over 20 runs and 1,000 hours of operation have already been completed without any power or telemetry loss. The system has saved 160 hours of operation time in Middle East from the implementation of the hybrid cable single-reel solution on four jobs that formerly required two CT strings. In the Norwegian continental shelf, the system saved between 24 hours and 32 hours in a single job by eliminating trips to surface to replace the batteries.
This new hybrid cable and its associated surface and downhole system provide a single solution for interventions, distributed measurements, and logging. Altogether, they pave the way for significant improvements in well intervention efficiency and open new avenues for more complex and demanding operational workflows.