Development and exploitation of oil and gas resources in increasingly difficult operating environments such as deepwater raise many technical challenges. Among these is the ability to provide assurance on the completions and production from high-cost and complex wells. Real-time, permanent wellbore and reservoir monitoring is a critical technology for providing assurance and maximizing profitability of these fields.
Recent developments in fiber optic sensing technology have resulted in reliable alternatives to conventional electronic systems for permanent, downhole production and reservoir monitoring. In-well fiber optic sensors are now being developed and deployed in the field for measuring temperature, pressure, flow rate, fluid phase fraction, and seismic response. Bragg grating-based fiber optic systems combine a high level of reliability, accuracy, resolution and stability with the ability to multiplex sensors on a single fiber, enabling complex and multilateral wells to be fully instrumented with a single wellhead penetration. These systems are being installed worldwide in a variety of operating environments for a variety of applications.
This paper presents several recent deployments of in-well fiber optic monitoring systems, including descriptions of the downhole sensor assemblies, installations, and measured data. Installations of fiber optic pressure and temperature systems in a land well and in the Gulf of Mexico and an all-fiber flow and liquid fraction system in deepwater Gulf of Mexico are discussed. A general description of fiber optic sensing and Bragg grating-based sensing systems is also presented.
The past several years have seen a great increase in the development, deployment and application of permanent in-well monitoring systems. Drivers behind this increase include new field developments in much more challenging, costly operating environments; the requirement to provide assurance on the production from these new fields; and the desire to optimize management of production and reservoir recovery.
Many large, new fields coming on line today and in the near future are being developed with relatively few high-cost, high-rate, complex wells. Intervention costs in these wells will be high or even prohibitive. This puts a premium on the value of real-time downhole data during production and on the use of this data to foresee and prevent well problems.
The large, up-front capital investment for many new field developments, such as deepwater, puts a tremendous importance on the assurance of producing the anticipated volumes of oil and gas in the anticipated timeframe, in order to make the required return. Downhole monitoring systems provide data to continuously assess the health of the well, optimize well operations, and provide assurance on the flow of oil and gas.
Real-time downhole data offer many opportunities to greatly improve production management and reservoir recovery. These include actively managing drawdown to increase production performance; production and injection profiling in horizontal and multi-zone wells to identify and control fluid flow to and from different parts of the well; providing sufficient information to allow for the early determination and confirmation of reserves; allowing for active reservoir management early in the field life; optimizing drainage; and increasing overall field recovery.
In most, if not all cases, the value derived from real-time, downhole monitoring systems greatly exceeds the cost and can be recovered early in the life of the well, IF these systems are reliable and perform as specified over the life of the well and IF the data are managed properly and used to their fullest potential. Fiber optic-based sensing systems being deployed today offer the promise of achieving the level of performance required to achieve this value.