To promote efficient recovery of bitumen hydrocarbons using the steam assisted gravity drainage (SAGD) process, 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 are designed to enhance the 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. This paper discusses the design and capabilities of FCDs.
The project initiated with a design requirement of two core components— the axial distribution of steam exiting the device and a device to incorporate a sliding sleeve mechanism. The basis for FCD design decisions was developed initially by reviewing worst-case operating conditions FCDs could encounter and then using this information 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 the erosive effects of varying steam quality, the critical velocities and erosive mechanisms were defined. API RP 14E provides a conservative basis to determine the maximum allowable fluid velocity in a given system, but several studies have sought to push the boundaries of acceptable fluid velocities. The most conservative nozzle exit velocities were used to limit risks to casing. The risks caused by high velocities in the nozzle inside/inner diameter (ID) to the injection tool were mitigated through the use of computational fluid dynamics (CFD) analyses and material selection/treatment.
Because of the high temperatures under which SAGD operates, consideration of mechanical property degradation and possible deformation had to be considered, specifically to the collet of the sliding sleeve. To prevent diminishing performance during the operational lifetime, FCDs that use sliding sleeves with collet mechanisms require a robust design that recognizes and addresses maximum stress loads and limits plastic deformation at peak temperatures. The testing of the sliding sleeve was conducted throughout a wide range of temperatures where the forces to shift the sleeve were monitored and compared to previous finite elements analyses (FEA) for compliance.
ISO 14998 Annex D provided the basis for function testing of the FCD (i.e., 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. Field performance is discussed in the paper.