When a control line becomes plugged due to contaminants in the hydraulic control fluid, or begins leaking due to corrosion, surface controlled subsurface safety valves become inoperable. As a result of these control line problems, productive wells can remain shut in due to failure of this critical safety valve device.
“Plugged or leaking control lines prevent surface-controlled tubing-retrievable safety valves from operating, which can result in lost production,” said Brian Champion, General Manager, Wireless Well Solutions for Expro. “This is not a new problem and applies globally.”
The most common remedial solution today involves the installation of a subsurface controlled safety valve (SSCSV) such as an ambient valve or storm choke. This is a relatively low-cost solution compared with performing a full rig-based workover to replace the safety valve and control line.
“The get-around solution is to install a storm choke or ambient valve,” Mr Champion said, “but these can perform unpredictably and they are not fail-safe or controllable from surface and thus not ideal remedial solutions.
“The industry wants a more dependable and safer (alternative) solution to storm chokes and ambient valves,” he continued, “and this drove Expro’s decision to develop FlowCATTM.”
FlowCAT, a retrofittable wireless controlled safety valve, has been in development for the past three years and is now entering commercialization. During development, Expro enlisted the support of Petrowell Ltd. to develop the mechanical valve component of FlowCAT for integration with Expro’s wireless telemetry and power technology. Additionally, Expro conducted a six month in-well qualification trial of the valve in an onshore gas well, which was very successful. FlowCAT was also an Offshore Technology Conference (OTC) Spotlight on New Technology award winner this year.
FlowCAT can be retrofitted into a well using conventional slickline intervention equipment and procedures. The fail-safe design valve is controllable from surface using Expro’s Cableless Telemetry System (CaTS) electromagnetic communication capability. A signal transmitted from surface keeps the valve open. If the signal is halted for any reason, the valve closes and provides a fail-safe system.
In mature fields, multilaterals drilled with through-tubing rotary drilling are being used to reach remote parts of the reservoir that are not being produced through the main wellbore. This scenario usually presents some challenges in being able to control flow from the lateral independent of the primary wellbore. Because CaTS is wireless, it is possible to communicate instructions to the flow control valve retrofitted into the lateral by sending electromagnetic signals from the surface, down the main wellbore and into the lateral. This is an application that Expro will be developing in the future as it proceeds to develop the tools necessary to deliver its “Retrofit Intelligent Well Vision.”
How it works
The FlowCAT system comprises a controller/transmitter located at the surface and with the valve, receiver and battery power supply modules located downhole. When the valve is first installed, it is held in the open position by an electro-mechanical latch mechanism and the repeated transmission of electromagnetic “stay open” commands. If the “stay open” commands are halted from the surface, for example, due to a power failure or a catastrophic event, the valve will close on its own after a pre-determined time lapse since the loss of signal occurred. The valve will also close if there is a loss of battery power.
Additional safeguards are built in. For example, FlowCAT is fully integrated with the wellsite’s existing safety system, with the surface transmitter module interfaced to the local emergency shutdown system (ESD). Should a controlled well shut-in event be initiated at the surface by activating the ESD system, a “close” command is transmitted to FlowCAT and it will immediately begin the close sequence.
After a valve closure event, the valve is reopened by the application of an over-pressure reset from surface.
Six month field trial
The topic of an SPE paper (SPE 130427) that was presented in Houston in March 2010, the valve system had a six month field trial in a gas well located onshore southern Italy. The 4 ½-in. FlowCAT valve was deployed into the San Salvo 54 gas storage well in the Fiume Treste Field via standard slickline intervention methods and was cycled and inflow tested regularly during periods of production and injection. Following installation, valve closure tests were performed monthly between January and May 2009. All of the monthly valve cycling tests were completed successfully and zero leakage was observed during all of the shut-ins.
Following the six month test, the valve was retrieved via slickline and recovered to surface for inspection. Detailed post-job analysis indicated that the valve had performed to specification with only normal wear and tear observed in the mechanical assemblies. Assessment of the six-month capacity battery pack concluded that an additional six to eight weeks duration was still available, which would have extended the valve’s actual performance to as long as eight months. A 12 month battery pack is also available.