Novel Fiber Optics Lateral Connector Tool for Subsea Intelligent Casing Applications: Results and Relevance for Design

Abstract

In subsea applications, our Intelligent Casing-Intelligent Formation Telemetry (ICIFT) Systems focus on using fiber optic sensing methods for lifetime monitoring of a well and its reservoir. The production casing and/or formation/cement outside the casing are instrumented with fiber optic cables that require continuity connections with other fiber optic cables that exit the wellhead. Two new technology tools are needed to join two fiber optic cables downhole laterally across an annulus. One is a "lateral" fiber optic (FO) pressure balance oil filled (PBOF) wet-mateable connector. The other tool needed and the one addressed in this articel is one that can align two FO cables with millimeter precision for connection laterally across an annulus. For that purpose, a downhole autonomous robot rendezvous tool is designed that can align two FO cables at a lateral crossover point with millimeter precision; two prototypes are constructed and tested. The setting of this research is to bring fiber optic cables through the wellhead in the annulus outside the production tubing, down through the production packer, and crossing laterally in the annulus over to the production casing. The autonomous robot rendezvous tool developed with prototypes and tested uses two subassembly designs: a tubing subassembly design and a casing subassembly design. The objective of the autonomous robot rendezvous tool is to align the two subassemblies with millimeter accuracy in two dimensions (i.e., in depth direction and in angular rotational direction). The designs of the two subassemblies are developed for popular subsea 7" OD production tubing and 9 5/8" OD production casing and for a completion fluids-based annulus environment (e.g., brine, water, and diesel). Test results of the two prototypes provide 5 mm "ballpark" accuracy for rendezvous alignment in the depth direction and 2 mm accuracy for rendezvous alignment in the angular direction. The development of the autonomous robot rendezvous tool is one step in the direction of making the reservoir intelligent outside the production casing via all means of distributive fiber optic sensing methods without the need for power and electronics downhole during the lifetime of well.