Cableless Telemetry System achieves world first in reservoir monitoring

While wireless telemetry has been researched for several years as a means of evaluating reservoir connectivity and monitoring reservoir pressures and temperatures on a long-term basis, the technology has only recently made significant gains in the field. One system at the forefront of the wireless telemetry wave is the Cableless Telemetry System (CaTS) from Expro International Group.

The casing is the cable

Unlike some well telemetry systems that are based on mud pulsing or the generation of acoustic waves in the tubing wall, CaTS is based on electromagnetic communication through the tubing and casing. Simply put, the technology works by applying a low frequency electrical signal to the production tubing or casing downhole, which then propagates to the surface and is picked up and recorded by a topside or subsea receiver to recover the required data in real time. This method of signal propagation eliminates the need for cables, electrical insulation of the completion or the use of completion systems with special electrical properties.

Expro claims a significant benefit with this technology is that no cable to surface is required for communications. However, under certain circumstances, transmission through the tubing or casing can cause attenuation of the signal and a reduced data transmission range.

Nonetheless, Expro states that useful ranges and data rates can still be achieved. For example, the company points to options such as data compression, various configurable data schemes, or duplex communications (surface to downhole, downhole to surface) as viable means of optimizing the data being sent from the downhole tools.

Data can be picked up at the wellhead or in some cases downstream of the wellhead, such as within the flowline/gathering station complex. Expro touts this as a particular benefit in areas with remote wellheads, where it is desirable to minimize the amount and value of equipment on the wellhead.

The standard sensor system for CaTS is a resonating quartz pressure and temperature transducer, reportedly the standard for well and reservoir monitoring in both long and short-term applications. CaTS can also be made available to operate with a range of different sensor systems, including valve position sensors, flow sensors, and sand production sensors, among others.

Because CaTS is cableless, the downhole tool must have its own power supply. Currently, the most reliable and consistent power source used is a standard lithium battery.

The technology may suffer range performance limitations on offshore platforms, where the signal becomes attenuated as it enters the platform structure. Expro states that this problem may be solved by installing a downhole signal pick-up below the seabed. By connecting the topside receiver to a suitable location downhole, where it is terminated in a small pressure housing, the wireless performance is reportedly vastly improved and is on par to a similar onshore well.

In spite of these challenges, Expro touts its wireless telemetry system as applicable for a variety of applications in the real-time monitoring of reservoir data where complex well configurations are implemented, such as:

• Long-term well and reservoir monitoring applications
• Artificial lift monitoring
• Monitoring of complex completions such as multi-laterals and gravel packs
• Data transmission over surface and subsea pipelines.

CaTS debuts in the North Sea

Earlier this year, Expro reported the first successful application of CaTS for the monitoring of reservoir pressure and temperature response in an abandoned subsea appraisal well in the UK North Sea.

As part of the final abandonment process of the BP-operated Clair Ridge appraisal well 206/8-T, CaTS was installed in June 2006 to record and store post abandonment reservoir pressure and temperature data. A subsea receiver collected, processed and stored the data at the seabed, after which the data was transmitted on demand to a supply vessel located above the abandoned well for analysis.

Expro states that further data interrogation visits are planned for later in the year, as BP monitors any interference effects resulting from production or injection activity on the nearby Clair platform. The information obtained from CaTS will also reportedly help BP gain a clearer understanding of the overall structure of the Clair reservoir.

To learn more about CaTS, click here, or refer to SPE paper 102547, presented at ATCE2006 in San Antonio, Texas.