Case Studies

Measurements on damaged fibre

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Sensornet’s distributed temperature sensor (DTS) system proves its ability to carry out world-beating, single-ended measurements on previously installed, but damaged, optical fibres on an offshore platform in Brunei.

Sensornet performed optical fibre health checks on three wells offshore in Brunei enabling Brunei Shell Petroleum to quantify the reliability of measurements taken from fibres that were thought to be damaged. As well as assessing the differential loss in the fibres on each well using a dual wavelength OTDR (optical time domain reflectometer) health-check system, Sensornet also provided Brunei Shell with distributed temperature measurements for comparison with those captured by the permanent DTS system already installed on the wells.

The result was clear confirmation of the Sentinel DTS system’s ability to detect and assess damage to installed optical fibres, and to provide accurate, calibrated, fine spatial and temperature resolution measurements. Sensornet performed all set-up, calibration and health-check measurements, and took highly accurate DTS profiles on the three wells in a single six-hour offshore visit. Many fine temperature features were resolved in the data which were correlated with known features in the well completion.

 

All the fibres had been installed using a “pump around” method in which fibre is inserted into a capillary U-tube running down the well, through a “turn-around” at the bottom, and back up to surface. The health check found immediate problems with the fibre in well ID-23, which was shown to be damaged significantly along its entire measurable length – so badly damaged, in fact, that meaningful simple single-ended measurements could not be made with this fibre.

Sensornet determined that with its health check technique, it could measure to around 2500m depth before the accumulated losses became too large for meaningful measurements. The condition of the fibres in the two other wells was shown to be much better, with no measurable degradation on well ID-19 and only small degradation on well BG-7 at all points past the “turn-around” sub. Here, the scale of the damage and its position at the end of the fibre was not expected significantly to affect the accuracy of DTS measurement, so single-ended measurements could be used with confidence.

 

 

The Sentinel DTS system used in the trials is a high-performance instrument with world-beating optical performance. It is contained in a transportable 19” rack mountable case with an inbuilt PC, flip-up monitor, keyboard, uninterruptible power supply and network connection. It provides long-range distributed temperature sensing with a resolution of less than 0.01°C if required.

On the Brunei Shell application, for example, it collected data at a 1°C temperature resolution with a 1m spatial resolution over 5km with an update time of 10 seconds. The offshore visit to the three Brunei Shell offshore wells proved the ability of the Sentinel DTS system to provide not only a health check on the condition of the installed optical fibres, but also a range of accurate spatial and temperature measurements within just six hours. The DTS readings showed excellent depth and temperature calibration.

As a useful quality check, Sensornet obtained a very good match between the DTS temperatures and the single point permanent downhole gauge in each of the wells. Sensornet provided its DTS data alongside an auto-scaling completion diagram as part of its well-specific data viewer tool. This allowed the user to readily correlate temperature features with features along the completion, such as individual perforated intervals.

This practical test has proved the potential of Sensornet’s distributed sensing technology in providing oil and gas operators with a rapid and reliable means of carrying out health checks on installed optical fibres. In the meantime, Sensornet technology is being actively applied in many other areas of the oil and gas industry – both on and offshore – as well as in the civil engineering, power utility, tunnelling and aerospace sectors.

 

Accurate results

Damage Assessment

 


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