Distributed Acoustic Sensing (DAS) for Gas and Oil Well Monitoring

A new generation of in-well monitoring technologies that are being characterized under the Acoustic Energy sensing banner has been recently developed. There are multiple monitoring techniques that may be classified under the same umbrella, like disturbance or vibration event monitoring; however, the distributed acoustic monitoring (DAS) technique has become popular for in-well monitoring applications.

Since the development of fiber optic technology, the fiber optic-based monitoring systems have been used in applications with extreme operating conditions, i.e. extremely high or low temperatures, physical space limitations, unique measurement requirements, etc. The electrical/quartz sensing technology has always had a temperature limitation of 150°C, which does not allow the use of these systems in industries and applications where high temperatures are often present. DAS systems, on the other hand, are based on fiber optic technology, which allows the systems to be used under much higher temperatures.

A distributed acoustic sensing system allows its user to listen to the acoustic field at every point along the standard telecom single-mode fiber optic cable, which can be several kilometers in length. The fiber optic cable is deployed in a well, where the system monitors its condition and registers production-relevant events. The optic fiber cable used in such a system can be loaded with many sensors, e.g. with a spatial resolution of 1 meter there will be 10.000 synchronized sensors along a 10.000-meter fiber optic cable. Distributed acoustic sensing systems utilize a novel digital optical detection technique to catch the full acoustic field with great precision: amplitude, frequency, and phase over a wide dynamic range. The main advantage of a DAS system is its ability to catch the acoustic field at every point simultaneously.

DAS systems use the combination of backscattered light and advanced signal processing to segregate the fiber into an array of individual microphones.

Traditionally, distributed acoustic sensing systems have been used in the defense and security industries; however, DAS systems are quickly becoming one of the most effective and cost-efficient ways of in-well monitoring, for example, oil and gas leakages. Another promising field of application of the DAS systems is in the area of hydraulic fracturing of tight-sand and shale-gas reservoirs. The first downhole field trial of a DAS system was conducted in 2009. The technology is sufficiently reliable and sensitive to be used during the fracture-stimulation treatment to monitor the in-well activities.

Distributed acoustic sensing systems can be retrofitted to existing installations of permanent in-well fiber optics-based monitoring systems with the addition of surface equipment. New installations of DAS systems are also possible and have already been performed.

If you are interested in DAS systems and want to learn more, please contact us at info@optromix.com

Fiber Bragg grating sensors for bolt force status monitoring

Over the past decades, bolts support has become a widely used method of roadway roof failure control due to the easy construction and its efficient reinforcement. Moreover, bolts support improve surrounding rock structure stability. Underground coal mining has been extending to deeper levels where high-stress conditions are present; high stress causes roof subsidence and floor heaving in coal mine roadways. This can have a negative effect on the safety of the miners and construction integrity. Therefore, real-time monitoring of bolts in coal mine roadways is vital for the long-term safety and stability of the surrounding rock structures.

The systems that are used currently for real-time status monitoring of the bolts support structures are easily affected by the harsh environments and high levels of stress. Fiber Bragg grating sensing technology provides a new and effective way of real-time measurements. FBG sensors have become one of the most promising optical fiber passive device applications. Fiber Bragg grating sensors have a variety of applications and are widely used for temperature sensing (FBG temperature sensors), pressure sensing (FBG pressure sensors), acceleration sensing (FBG accelerometers), deformation sensing (FBG displacement sensors), etc.

FBG sensors have multiple advantages over traditionally used measurement equipment: FBG sensors are immune to electromagnetic interference, have a strong multiplexing ability, high reliability, and sensitivity. Fiber Bragg grating sensing technology is already used in a variety of applications, like geotechnical engineering, structural engineering, civil engineering, tunnel construction engineering.

The use of FBG sensors in engineering applications shows that fiber optic sensors can automatically acquire, and monitoring results are of great significance in roadway anchorage engineering safety and bolt support quality evaluation.

Optromix, Inc. is a U.S. manufacturer of innovative fiber optic products for the global market, based in Cambridge, MA. Our team always strives to provide the most technologically advanced fiber optic solutions for our clients. Our main goal is to deliver the best quality fiber optic products to our clients. We produce a wide range of fiber optic devices, including our cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems.

If you are interested in Optromix FBG sensors, please contact us at info@optromix.com