Today operators in highly fractured carbonate reservoirs use running wireline gradiometric surveys as a traditional way of oil-rim movement monitoring. Nevertheless, the method is not ideal because it does not allow providing the necessary information in a manner timely enough to influence operations since the surveys are conducted just a few times a year. Distributed temperature sensing (DTS) system is an alternative solution that overcomes these drawbacks.
Distributed temperature sensing offers real-time monitoring of the oil rim in carbonate reservoirs. DTS technology is based on the use of optical-fiber Bragg gratings (FBGs) and is able to measure pressure in extreme environmental conditions. It should be noted that the DTS system does not require electronics, herewith it provides long service term even at elevated downhole temperatures. Also, distributed temperature sensing is quite stable, it can determine even small pressure changes.
Moreover, dozens of distributed temperature sensors can be implemented on one fiber optic cable connected to the FBG interrogator. The principle of operation includes a diaphragm pressure transducer that converts changes in the hydrostatic pressure of its environment into the deformation of a pressure-sensitive diaphragm, and then into the strain, within an optical fiber attached to the diaphragm. The thing is that optical fibers offer numerous advantages for oil and gas industry application, containing the following:
- high transmission efficiency that means the FBG interrogator can be installed several kilometers away from the downhole sensors;
- high data quality and accuracy due to data encoding in the light wavelength;
- data immunity to the electromagnetic influence by machines;
At present time the information about pressure and temperature measurements, as well as system-health and self-diagnostic information are transmitted from the FBG interrogator into a database at 3-hour intervals. If fresh data sets are obtained, an algorithm processes them into gas/oil-contact and oil/water-contact locations. Also, it is possible to visualize pressure, temperature, and fluid-level data to see them in real-time.
Further improvement of the DTS system will allow the application of the system for the production monitoring in ultrahigh-temperature thermal-recovery wells, where fluid temperatures up to 280 °C can be reached. Finally, distributed temperature sensing provides the reduction of a production delay, the reduction of operational costs, health, safety, and environmental risk reduction, and the possibility of system expansion.
Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating sensors, FBG interrogators and multiplexers, Distributed Acoustic Sensing (DAS) systems, Distributed Temperature Sensing (DTS) systems. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in temperature measurement systems and want to learn more, please contact us at info@optromix.com