The adoption rate of optical sensing technology for in-well permanent monitoring has accelerated dramatically since first introduced more than 10 years ago and a number of optical sensor types, including pressure, temperature, distributed temperature, seismic, and flowmeters have been commercialized. Although optical sensing technology has a demonstrated track record and gained industry acceptance, large-scale, field-wide commercial deployment has been slow. This paper describes a recent example of field-wide optical sensing deployment with a planned scope of 27 wells. Multiple in-well sensors were installed in the newly developed Buzzard Field, operated by Nexen Petroleum U.K. Limited in the North Sea. This paper explores the initial results after the first 13 well completions. An assessment of the major project phases from definition, planning, and system selection to project execution, site integration testing, installation, and early life operation of the optical technology is included. A number of lessons in equipment and system design, execution, and data management have been learned and are also discussed in the paper. Whilst field development is ongoing, the initial success rates show that satisfactory performance has been obtained in all key areas including data availability, delivery, and post-processing. This case study demonstrates that innovative optical sensing technology and downhole flow measurement is ready for large-scale adoption with minimal risk. This is an important and timely finding as the industry is introducing optical monitoring into large subsea fields.

This paper describes the use of sound speed in flow measurement applications in the high-pressure/high-temperature downhole environment. The propagation speed of a sound wave is a powerful tool to extract useful information from a flowing fluid medium in pipe whether the medium consists of a single-phase or multiphase flow. Considering the complex nature of the flow patterns and changing phase fractions from reservoir to surface, utilizing the propagation speed of sound of a fluid mixture is not a trivial task, especially if the interest is real-time flow measurement. The demanding applications span a wide spectrum from noisy medium originating from fast-moving gas/liquid flows to quiet medium originating from slow-moving liquid/liquid flows. In the current work, multiple flow loop tests are conducted in different facilities to evaluate the direct use of sound speed in flow rate measurement and the results are associated with real-life field examples. A tool analysis map is developed that addresses the use of sound speed for flow measurement under different scenarios. Although most examples are based on strain-based local sensing of the flow, the use of sound speed is independent of the methodology and can be implemented by other methods such as acoustic-based distributed sensing.

A new three-phase downhole flow measurement methodology is developed based on measurements of speed of sound at different locations along the well, where the pressure is greater than the bubble-point pressure at the first location and smaller at the second location. A bulk velocity measurement is also required at the second location. The fluid at the first location is a mixture of two phases, but becomes a mixture of three phases at the second location due to the liberation of gas from the oil phase. The flow equations are first solved for two-phase flow at the first location to obtain the first phase fraction, water-in-liquid ratio, and then this information is fed into the flow equations after adjustment to the local pressure and temperature conditions to solve for three-phase flow at the second location to obtain the second phase fraction, namely the liquid volume fraction. These two phase fractions along with the bulk velocity at the second location are sufficient to calculate the three-phase flow rates. The methodology is fully explained and the analytical solutions for three-phase flow measurement is explicitly provided in a step-by-step process. A Lego-like approach may be used with various sensor technologies to obtain the required measurements, although distributed acoustic sensing systems and optical flowmeters are ideal to easily and efficiently adopt the current methodology. This game-changing new methodology for measuring downhole three-phase flow can be implemented in existing wells with an optical infrastructure by adding a topside optoelectronics system.