Tendeka’s Garth Naldrett and Tor Inge Åsen explore the implications for operators of adopting wireless technology for downhole monitoring
The trend of increasing wellbore complexity for extended reservoir contact, and greater reservoir heterogeneity, are demanding improved monitoring and control solutions.
Traditionally the only option has been the deployment of a cabled system but this limits the application of intelligent well technology to new installations or workovers.
In any case, cabled systems are not always possible in new installations, especially where the completion is discontinuous, and slim hole or monobore completions may not allow cables to be deployed along the tubing string.
Wireless technology is proving a more flexible alternative to addressing the issues of permanent downhole monitoring. One product, Tendeka’s wireless gauge, which has been successfully deployed in the North Sea, allows real time flowing bottom hole pressure (FBHP) to be efficiently transmitted to surface, an attractive option for wells where the cabled gauge system has failed, or was not initially installed.
Originally designed to 3.5”, the company has produced a 2.25” version which has trialled successfully in the North Sea and is expected to have a wider global appeal
Benefits of Wireless Technology
The system transmits data from the lower completion to the surface via pressure pulses. A novel tool design allows the well’s production to be partially choked for a very short time to create a pressure pulse, which is detectable on the surface pressure gauge.
The well’s energy is used to transmit data to surface, thereby reducing power consumption, and the system requires no additional surface installation or pickup, since an existing tubing head pressure gauge can be used to detect the pulse train.
For most operators, the system can be deployed by a single intervention, allowing highly accurate data to be sourced almost instantaneously for a fraction of the cost of a re-completion.
Compared with a memory gauge system, it allows data to be collected in real time and provides a continuous confirmation of operation. The gauge can be set in blank pipe, giving optimal freedom for installation depth, and it can be installed as close to the producing interval as required.
A significant benefit of using pressure pulse transmission is the ease of installation. No retrofitting of topside equipment is required, and many of the technical and contractual issues when introducing a new monitoring system are avoided.
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Successful Deployment
A major operator in the North Sea retrofitted the 3.5” wireless pressure and temperature gauge at 2,200m in a low pressure (32 bar) gas well offshore Norway. The existing wellhead pressure sensor was used to capture the wireless signal and extract the data, therefore no extra infrastructure was required.
The application was especially challenging as the well was a marginal producer and the wellhead pressure had large background pressure variations due to the limited well deliverability.
Despite these conditions, pressure pulse transmission proved effective. Even if the well starts to significantly deplete while the wireless downhole gauge is installed the gauge itself will modify its pressure pulsing method to ensure a detectable pulse train is transmitted to surface.
The wireless gauge is unable to transmit signals in a non-flowing or shut-in well because a flow regime is required to produce the pressure pulses.
The tool can record PBU (pressure build up) data during shut-in periods, and once well production is restarted the stored data can be transmitted to surface.
During this actual installation, there were periods of shut in while surface maintenance was conducted. The tool successfully recognized the shut in events and entered its power saving hibernation mode.
When the well resumed production, the technology re-activated itself and the first telegrams transmitted following the restart, gave accurate shut in pressure data to surface.
Figure 1 (on page 27) shows a comparison between the topside wellhead decoded data and the data sent from the tool itself. A third party memory gauge was installed as back-up below the wireless gauge to confirm pressure readings. It shows the readings to be accurate.
This application, and two others undertaken at the time, demonstrated that the system functions not only in oil wells, but also in gas wells and wells with a high gas/oil ratio.
It was demonstrated that the wireless gauge could function in wells with slug flow and high levels of pressure/noise variations on surface. During shut in periods the tool successfully recorded the shut in data and transmitted it to surface when production was resumed. The 2.25” version of the gauge was recently successfully tested in another gas well in the North Sea.
Wide Ranging Application
The downhole pressure temperature gauge can operate in water injection wells, where a back pressure is created instead on the injection fluid, which generates a pressure pulse train on the surface.
A recent development in the wireless technology products now also allows the measurement of injection rate. By measuring the pressure drop across a modified venturi an accurate flow rate can be calculated.
Flow loop testing has verified the method is extremely accurate when used in single phase fluids, such as with water injection applications.
This allows the gauge to be run between injection intervals, reporting on the pressure, temperature and rate split between zones. The information is then transmitted to the surface using wireless telemetry.
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Activation Systems
The susceptibility of downhole mechanical pressure counting activation mechanisms to debris ingress has resulted in numerous in-well failures of these systems. Using a built in pressure transducer, the wireless technology is able to detect pressure pulses from the surface.
Unlike mechanical systems, which become jammed when covered in debris, electronic systems are still able to register pressure changes applied from surface even through a few meters of barite or other wellbore debris.
Furthermore electronic systems are fully programmable to detect a pressure sequence that cannot be accidentally created in normal operations.
In the event of pressure pulse transmission not reaching the tool the electronics can be programmed to activate at a preset time interval. The final backup is an acoustic pickup, which receives a signal from a downhole tool hundreds of meters away.
Two systems have been developed based on the surface to bottom hole wireless communication. The first allows the opening of a completion plug without intervention.
The development was driven by an operating company struggling to recover completion plugs after high pressure stimulation from above. It is suspected the high differential pressure across the plug causes sufficient deformation for the completion plug to become permanently attached to the nipple profile.
In the replacement wireless system, rather than recovering the completion plug, the wireless plug opens its flow ports in response to the programmed signature, allowing production or injection to take place across the device.
This not only saves the single wireline run to recover the plug, but a potentially large fishing operation for plugs that have become permanently fixed to the nipple profile.
The second wireless activation system provides a remote firing signal for downhole barrier plugs, providing a reliable alternative to the suppliers’ mechanical ratchet style activation.
Downhole barrier plugs are especially susceptible to debris since any fallout while running the upper completion ends up on top of the barrier plug and around its mechanical activation port.
The wireless pressure monitoring system does not suffer from these problems. It has a substantially charged pressure chamber which is released to activate the barrier plug on receipt of the appropriate signaling from surface.
Inflow Control
The latest developments in wireless technology now allow these systems to operate inflow control valves. This will bring with it a change in the way operating companies design, test, stimulate and operate maximum reservoir contact wells.
Locations that could not previously be controlled can now be using wireless signaling. Combing lower completion technology, incorporating zonal isolation packers and inflow control devices, with that of the wireless downhole devices allows new methods of reservoir inflow control to be developed.
As each wireless inflow control valve is autonomous no cabling is required between devices, allowing a large cost saving in control lines and downhole connectors. Drillers are also offered more flexibility in rotating the completion while running in hole without risking damage to externally strapped control lines.
Conclusion
The wireless retrofittable downhole pressure and temperature gauge provides a reliable and cost-effective alternative to cabled systems, and avoids the need for a workover for installation. Data can be transmitted to and from the wireless devices, allowing operation in a monitoring or control scenario.
Wireless telemetry is equally effective for transmitting data from bottom hole to surface, or from surface to bottom hole. Top down communication allows more effective wireless activation devices to be developed for stimulation control, or for controlling downhole barrier plugs.
Wireless inflow control valves will enable completely new and novel methods for completing complex wells at lower cost, less disruption and lower drilling risk.
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About the Authors
Garth Naldrett
Vice President Monitoring and Control – Garth Naldrett joined Tendeka through the acquisition of FloQuest in 2009, a business he founded in 2006.
Prior to joining Tendeka, Garth held various positions within Schlumberger including product champion for fibre optic monitoring and project engineer for subsea monitoring.
With 15 years oil and gas industry experience Garth brings knowledge in completions, reservoir monitoring and interpretation. Garth holds a BSc in Electronic Engineering from the University of Cape Town and an MSc in Electrical Engineering also from the University of Cape Town.
Tor Inge Åsen
Team Leader Wireless development – Tor Inge Åsen joined Tendeka through the acquisition of Well Technology in 2007, a business he joined in 2005.
Prior to joining Tendeka, Tor Inge held a position as project engineer at Well Technology and R&D engineer at Simrad. With six years oil and gas industry experience Tor Inge brings knowledge in reservoir monitoring and control. Tor Inge holds a BSc in Electronic Engineering from the University of Stavanger.
