Juun van der Horst

Fibre Optic Sensing for Improved Wellbore Surveillance

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.

On the stress change in overburden resulting from reservoir compaction Observations from two computer models and implications for 4D seismic

Production-induced depletion of hydrocarbon reservoirs leads to deformation, compaction, displacements, and stress change in the reservoir as well as in the surrounding rock. Such stress changes affect the acoustic-wave velocity and bulk density. This has two implications. It changes the contrast in acoustic impedance between reservoir and overburden, resulting in seismic amplitude changes at the top of the compacting reservoir. Secondly, it changes the traveltime of seismic reflection waves, leading to arrival-time delays (time shifts) of seismic data gathered in the repeat survey compared to data gathered in the base survey (Hatchell et al, 2004; Kenter et al, 2004; Stammeijer et al, 2004). Maps of time shifts can then indicate the areal distribution of reservoir compaction, and thus reveal the areal distribution of depletion. This could help to locate bypassed oil in undrained compartments, identify drilling targets and sidetracks, and avoid expensive infill wells. These interesting geophysical applica...

Fibre Optic Sensing For Improved Wellbore Production Surveillance

Since our previous publication1 significant progress has been made to further mature the application of Fiber-Optic (FO) based Distributed Acoustic Sensing (DAS) for production and injection profiling. A considerable number of new field surveys were conducted to further improve the evaluation algorithms or workflows which convert the DAS noise recordings into flowrates from individual zones. For gas producing wells, a new graphical user-interface has been developed that allows the user to visualize and QC the data in real time. Additional flow and visualization software have been developed for single phase gas producers to enable the user to select and evaluate the data in a user-friendly manner using the most up-to-date evaluation algorithms. There are still improvements to be made in enabling Distributed Sensing infrastructure, such as handling and evaluation of very large data volumes, seamless FO data transfer, the robustness & cost of the FO system installation, and the overall integration of FO surveillance into traditional workflows. It will take some time before all these issues are addressed but we believe that FO based applications will play a key role in future well and reservoir surveillance. In this paper we present two recent examples of single-phase flow profiling using DAS. The first example is from a single-phase gas producer in one of the Unconventional plays in North America and the second example is from a long horizontal, smart polymer injector operated by Petroleum Development Oman (PDO).