The trend of increasing wellbore complexity for extended reservoir contact, and greater reservoir heterogeneity along the contact, are demanding improved monitoring and control solutions. Tendeka's Garth Naldrett and Tor Inge Åsen review recent wireless wellbore advances offshore Norway.
Permanent downhole monitoring is by no means new to the oil & gas industry. The earliest SPE paper reference for a permanently cabled pressure and temperature monitoring system dates back to 1963, yet despite its maturity industry uptake of permanent cabled monitoring systems is relatively low.
The trend of increasing wellbore complexity for extended reservoir contact, and greater reservoir heterogeneity along the contact, are demanding improved monitoring and control solutions.
Traditionally the only option for enabling these solutions was the previously mentioned cabled systems, limiting the application of intelligent well technology to new installations or workovers. Cabled systems are not always possible in new installations, especially where the completion is discontinuous, such as with two-trip completions or multilateral wells. Slim hole or monobore completions may also not allow cables to be deployed along the tubing string.
These complexities, along with the cable cost and associated non productive time running such cabled system are all factors contributing to a relatively low overall market penetration.
However, new wireless technology is proving a more flexible alternative and addresses all of these issues.
Tendeka has over seven years' experience in the development, testing and deployment of wireless wellbore solutions as a feasible alternative to cabled systems. The first incarnation of a wireless system was the Tendeka Wireless Gauge, with systems being deployed in the North Sea since 2008. The wireless gauge 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.
The Tendeka wireless system uses pressure pulses to transmit data from the lower completion to surface. Through a novel tool design, the well's production is partially choked for a very short duration to create a pressure pulse, which is detectable on the surface pressure gauge.
This method has a number of advantages, in particular having very low power consumption, since the well's energy is being used to transmit data to surface. The system also requires no additional surface installation or pickup, since an existing tubing head pressure gauge can be used to detect the pulse train. This means that for the majority of operators, the system can be deployed by a single intervention, allowing for 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.
Using a wireline set packer to deploy the system, the gauge can be set in blank pipe, therefore giving the optimal freedom with regards to installation depth. The alternative is to set it using a wireline set lock, which is generally more cost effective than the wireline set packer option, however, this does limit the installation location to where there are wireline nipple profiles in the completion. The gauge system can be installed as close to the producing interval as required.
The innovative nature of using pressure pulse transmission is the ease of installation. No retrofitting of topside equipment is required, avoiding many of the technical and contractual issues when introducing a new monitoring system.
The system is also extremely power efficient, as it is the reservoir's inherent energy (not that of the battery pack) being used for carrying pulses from bottom hole to surface. The power consumption does, therefore, not increase at greater depth passing on a major benefit to the customer in terms of longer battery life and tool operation.
A common misconception, most likely due to limitations in MWD telemetry systems, is that pressure pulses cannot be utilized in the presence of free gas. Significant testing, modeling and field testing has shown the method is equally effective in oil and gas producing wells, with some of the latest systems even being designed for operation in water injection wells.
A major operator in the North Sea recently deployed the Retrofit Wireless Pressure & Temperature Gauge at a depth of 2200m 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.
During the installation planning, there were questions about the effects of free gas attenuating the signal. However, once the wireless gauge was installed at depth, the signal pulse proved to be easily distinguishable. 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. Therefore, the wireless technology has been qualified to transmit pressure pulse based signals even in low pressure gas wells, thereby demonstrating that the wireless downhole telemetry can be applied in nearly all fluid compositions and flow regimes.
The downhole tool has considerable built-in intelligence such that the choking mechanism is constantly modified according to the flowing conditions. 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 due to an actual flow regime being required to produce the pressure pulses. The tool has been designed to be able to be programmed to 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.
The figure (below) compares the topside wellhead decoded data with 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 showed them 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. During the trials, it was demonstrated 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.
Injection rate monitoring
The downhole pressure temperature gauge is also able to operate in water injection wells, where a back pressure is created instead on the injection fluid, and in a similar manner generating a detectable positive 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. All this information is then transmitted to the surface using wireless telemetry.
Wireless activation The susceptibility of downhole mechanical pressure counting activation mechanisms to debris ingress has resulted in numerous in-well failures of these systems.
Due to these limitations and the resulting lost time incidents Tendeka was approached by a major operator requesting an alternative electronic activation method.
Using a built-in pressure transducer, the wireless technology is also 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 system allows the opening of a completion plug without the need for 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 for reasons mentioned above. The wireless activation system has a substantially charged pressure chamber which is released to activate the barrier plug on receipt of the appropriate signaling from surface.
Inflow control valves
The latest developments in wireless technology now allow these systems to operate inflow control valves. This will bring with it a step change in the way operating companies design, test, stimulate and operate maximum reservoir contact wells.
Locations that could not previously be controlled, such as within the laterals of a multilateral well, or at the furthest extent of a long open hole lateral, can now be controlled using wireless signaling.
Combining the experience of Tendeka's lower completion technology, incorporating zonal isolation packers and inflow control devices, with that of the wireless intelligent downhole devices allows new and effective 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.
The drilling department is also offered more flexibility in rotating the completion while running in hole without risking damage to externally strapped control lines.
Reliable and accurate monitoring is crucial to efficient well operations. Tendeka's 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. The realisation of wireless inflow control valves will enable completely new and novel methods for completing complex wells at lower cost, less disruption and lower drilling risk. OE
|Garth Naldrett is Tendeka's vice president, monitoring and control. He founded FloQuest, a business acquired by Tendeka in 2009, and had previously served as Schlumberger's fibre optic monitoring product champion and project engineer for subsea monitoring. He holds a BSc in electronic engineering and an MSc in electrical engineering from the University of Cape Town.
|Tor Inge Åsen is Tendeka's team leader, wireless development. He was a project engineer at Well Technology prior to its 2007 acquisition by Tendeka, and earlier worked as an R&D engineer at Simrad. He holds a BSc in electronic engineering from the University of Stavanger.