Fiber Optic (FO) sensing technology is an exciting and novel technique offering many advantages over traditional wellbore surveillance methods1-3. Multiple FO cables can be installed that can be designed for sensitivity to a wide variety of signals such as temperature, pressure4-5, strain6-7, sound8, and the presence of specific chemical compounds. Permanently installed FO cables enable a cost effective surveillance policy where data acquisition surveys can be conducted without well interventions, in real-time, at any time, and continuous along the entire well bore. The avoidance of well intervention eliminates production deferment and operational risks of conventional surveys. Frequent, time-lapse FO based surveys can provide critical reservoir surveillance data for production and recovery optimization.
One instance of fiber-optic surveillance is Distributed Sensing, which uses the entire fiber as a sensing element. Recently, very good progress has been made in Distributed Acoustic Sensing (DAS) for hydraulic fracturing monitoring9, production profiling for commingled oil and gas producers, injection profiling for water injectors10, gas lift monitoring and the acquisition of wellbore seismic data such as Vertical Seismic Profile (VSP) surveys11-12. These applications are also seen to benefit from integration with other methods such as Distributed Temperature Sensing (DTS) and Distributed Pressure Sensing (DPS). In terms of wellbore surveillance, the possibility to monitor flow along the entire wellbore from FO sensing provides useful insights in the complex flow behavior in a well which can be used to optimize well performance.
There are also many improvements to be made in the enabling Distributed Sensing infrastructure such as the handling and evaluation of very large data volumes and seamless FO data transfer, the robustness & cost of the FO system installation, and the overall integration of FO surveillance into the full workflows. It will take some time before all these issues are addressed but it is clear that FO based applications will play a key role in future well and reservoir surveillance.
In this paper some examples of using DAS for Production Allocation are discussed.