Lowering total cost of ownership (TCO) has been a significant driver for adopting distributed acoustic sensing (DAS) over alternative surveillance techniques. For subsea wells, topside DAS requires optical engineering solutions to compensate for the reduced acoustic bandwidth, optical losses and back reflections accumulated through umbilicals, multiple wet- and dry-mate optical connectors, splices, optical feedthrough systems, and downhole fibers and wet mates. To obviate these problems, we describe a subsea fiber topology with two transmission fibers from the topside to an optical circulator deployed in the optical flying lead at the subsea tree equipped with an optical feedthrough system. This limits the sensing fiber portion of the total fiber length to only be the fiber located below the subsea tree, while eliminating all back reflections from the multiple subsea connectors above the remote circulator. The acoustic sampling frequency is only constrained by the fiber length below the subsea tree; thus enabling dry-tree equivalent sensing of both upper and lower completions regardless of the tie-back distance. This implies that the various spectral-based DAS processing algorithms developed for sand control, inflow profiling, well integrity, and seismic imaging on dry-tree wells can be equally and readily applied to DAS data acquired from subsea wells going forward. Results from various laboratory and field trials which validate system performance are presented, and deployment in subsea projects is discussed.
Presentation Date: Monday, October 12, 2020
Session Start Time: 1:50 PM
Presentation Time: 2:40 PM
Location: 361F
Presentation Type: Oral
