Merit of flow-control devices in SAGD oil recovery evaluated
CALGARY, Alberta -- Use of flow-control devices (FCDs) is the latest trend in SAGD oil recovery practices, according to a paper presentation during the SPE Heavy Oil Conference in Calgary this week. As noted by lead author Ryan McChesney, a mechanical engineer in the Completion Tools Development unit of Halliburton, to promote efficient recovery of bitumen hydrocarbons using steam-assisted gravity drainage (SAGD), it is vital that steam be used effectively, because steam generation constitutes one of the largest operational expenses during the SAGD process.
To optimize this process, steam-injection flow-control devices (FCDs) have been developed. “These devices,” explained McChesney, “are designed to enhance an operator's ability to distribute steam along the wellbore and to cease steam injection at a particular injection point if necessary, as the steam chamber matures.”
A design and testing project, conducted by Halliburton in partnership with Southwest Research Institute, began with a design requirement of two core components—axial distribution of steam exiting the device, and a device to incorporate a sliding sleeve mechanism. The basis for an FCD design was first developed by by reviewing worst-case operating conditions that FCDs could encounter, continued McChesney. Then, this information was used as the operating envelope criteria that the design should meet.
SAGD completion tools are required to endure everything from temperature fluctuations and corrosive formation fluids to erosive wet steam and severe wellbore trajectories. To design a tool that would survive erosive, varying steam quality, critical velocities and erosive mechanisms were defined, noted McChesney. He said that while API RP 14E provides a conservative way to determine maximum allowable fluid velocity in a given system, several studies have tried to push the boundaries of acceptable fluid velocities. However, the project used the most conservative nozzle exit velocities, to limit risks to casing. The risks caused by high velocities inside the nozzle to the injection tool were mitigated by using computational fluid dynamics analyses and material selection/treatment.
“Because of the high temperatures in SAGD operations, we had to consider mechanical property degradation and possible deformation, particularly to the collet of the sliding sleeve,” said McChesney. He added that to prevent diminishing performance during the operational life, FCDs that use sliding sleeves with collet mechanisms must be designed robustly, so that it handles maximum stress loads and limits plastic deformation at peak temperatures. McChesney said that testing of the sliding sleeve was conducted throughout a wide range of temperatures. The forces to shift the sleeve were monitored and compared to previous “finite elements analyses” for compliance.
McChesney said that ISO 14998 Annex D was the basis for function testing of the FCD, including cycling the sleeve and pressure testing at temperature. All pressure and function testing was performed at or above the operating temperature, and pressure and results were qualified to ISO 14998 V1.
