Apr 24, 2017Global oilfield services company Weatherford has expanded its existing RFID technology programs to manage the operation of downhole tools during the hydraulic fracturing and stimulation processes. For nearly a decade, the company has been developing radio frequency identification to control downhole tools, which are deployed into a well during drilling and completion operations (see Oilfield Services Company Embeds RFID in Drilling Reamers and Weatherford Enhances Downhole Drilling Operations Via RFID).
During the past two years, Weatherford has developed a new system that employs RFID to remotely control hydraulic fracturing processes by triggering the opening and closing of valves to control the movements of fluids as much as 5 miles below the surface or underwater.
The system reduces intervention costs and risk by cutting the amount of time required to operate the highly expensive equipment traditionally used to manipulate downhole tools. What can take two days with manually actuated tools, says Euan Murdoch, Weatherford's RFID completions product line manager, can be accomplished within a matter of a few hours with RFID.
Weatherford is one of the largest oilfield services companies providing technologies and services for formation evaluation, well construction, completion, stimulation and production.
Hydraulic fracturing is a technique by which rock is fractured by pumping down pressurized liquid to stimulate oil or natural gas reservoirs. To accomplish this, companies inject fracking fluid that can include water and sand into a reservoir, thereby creating additional cracks through which oil or gas can flow.
The AutoFrac system uses passive 125 KHz low-frequency (LF) RFID. During the fracking process, service providers must insert mechanical tools into the wells, and those tools accomplish such tasks as opening or closing valves and sleeves that control the passage of fluids from the well to the surface, or in the other direction. These valves and sleeves are often very far from the surface. The use of RFID to actuate downhole tools enables personnel at the surface to address a specific tool without affecting the other tools in the string, or to operate a tool after a specific delay period. When tags are not able to be circulated, operators use a sequence of pressure cycles in the injected fluids to accomplish the switching of valves or opening and closing. Combining these technologies creates the ideal operational logic to maximize the well's productivity.
Weatherford has developed its own RFID-based solution, Murdoch explains, which has been deployed in the North Sea and elsewhere.
The 125 KHz LF RFID interrogator and antenna are built into each of Weatherford's downhole tools. Because of the flexibility of RFID actuation, there could be approximately 35 to 40 such RFID-equipped tools in the well at any given time. The readers are designed to withstand up to 30,000 PSI in pressure, as well as high vibration and temperatures of 150 degrees Celsius (302 degrees Fahrenheit). These tools, inserted into well holes, are tubular in design, so they have an empty space in the center of the tube. This space enables the passage of fluids, while also serving as a channel through which RFID tags can flow.
The tag is deployed in a silicon carrier through the center of the tubular tools. "It looks like a jellyfish," Murdoch says. Before the tools are inserted into the well, the tag is programmed to recognize the unique ID number of a specific tool down-hole that will need to open or close a valve. Pressurized fluids push the tag through the 2.5- to 6-inch diameter tube toward the valve for which it is destined.
When the tag comes within range of the correct RFID reader, the device recognizes the tag transmission, which executes the command to open or close the appropriate flapper or sleeve. At the surface, workers know that the system is functioning properly when they detect a pressure change within the well, thereby indicating a valve has been opened or closed successfully.
The AutoFrac system was first put to use in the North Sea in the Netherlands in 2015, the company reports, where it has been reducing the amount of time required for the intervention process, from about four days per zone (there are typically around seven zones in a single offshore well) to approximately 12 hours with RFID.
With the decline of oil prices in the last few years, Murdoch says, the technology has become important in reducing costs in the field. "It comes down to saving rig time and reducing risk, to allow our customers to produce oil more cost effectively," he states.
Although the technology—which Weatherford designed and manufactured—is relatively simple, Murdoch says, ensuring that it works in the extreme downhole environment has been highly complex. "We've spent a lot of time in designing the RFID system," he adds, in order to ensure that the antennas can transmit and receive signals despite the high level of metal present in a downhole environment.
