This paper discusses the first fiber-optic (FO) installation in a vertical high-pressure high-temperature deep gas well in PDO, Oman. A specially designed fiber-optic cable was successfully installed and cemented behind the production casing, which was subsequently perforated in an oriented manner without damaging the cable. This paper also describes how the fiber-optic cable was used afterwards to acquire Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) data for the purpose of hydraulic fracturing diagnostics.
Fiber-optic surveillance is becoming an increasingly important activity for well and reservoir surveillance. The added complexity of the fiber-optic installation will affect the well design, which is one of the elements that requires focused attention, especially when the fiber is installed behind casing. The impact on casing design, wellhead design, perforation strategy, and logging requirements will all be discussed.
In order for a well to be completed with a permanent fiber-optic cable, a few critical procedures need to be followed, including:
modifying the wellhead design to include feedthrough ports for the cable;
optimizing the cement design;
imposing strict procedures to ensure the cable is installed behind the casing without getting stuck;
changing the perforation phasing to avoid damaging the cable;
mapping the location of the cable to allow the gun string to be oriented away from the cable.
The fiber-optic cable itself needed to be designed to be protected in such a way that it would not be damaged during installation and completion (perf/frac) activities. Furthermore, the cable was also optimized to improve its detectability, to aid the oriented perforation.
In deep gas wells, much more than in conventional shallow water injectors or oil producers, the well integrity aspect should be given special attention. Specifically, any risks related to unwanted gas leaks, either through the control line, poor cement, or because of other design errors should be avoided. In deep gas wells, high temperature and pressure will also play a big role in the expected lifespan of the cable.
Finally, the well was hydraulically fractured in four stages, using the "plug-and-perf" technique, during which DAS and DTS data were acquired continuously and across all depths of the well. The data provided valuable information on the effectiveness of each of the frac stages, it could be used to analyze screen-outs and detect out-of-zone injection, and recommendations for the optimizations of future hydraulic frac designs could be derived. The fiber-optic data were also integrated with other open-hole data for improved understanding of the reservoir performance. The next step will be to acquire repeated time-lapse DAS and DTS data for production profiling, to gain more insights of how the long-term production performance is affected by the hydraulic frac operations.