Accurate and reliable subsurface pressure and temperature (PT) measurements facilitate SAGD production improvements. The dynamic nature of the SAGD process requires real-time control of subsurface temperature and pressure to better manage subcool and steam-oil ratio (SOR). With SAGD operating temperatures in excess of 250°C (482°F), the use of several fiber optic sensing technologies have been explored for more than a decade with variable results. The successful implementations are designed with proven optical technologies that can operate in the harsh and aggressive SAGD operating environments. Fiber Bragg grating (FBG) based array temperature sensing (ATS) and glass Cane™ technologies have been field proven to withstand ultrahigh temperature and hydrogen-rich SAGD environments.
We describe the unique aspects of fusing FBG and glass Cane technologies to provide a stable sensor for such harsh conditions. Qualification testing of the Cane-based optical PT gauge for accurate and reliable subsurface measurements and the results and analysis of the field trial are also presented for the initial 12-month period covering the conditioning and production phases.
The lab qualification and test plans are presented to validate the specifications of the optical Cane PT gauge designed for all SAGD operational conditions. The lab tests consisted of multiple thermal and pressure cycling, vibrations, and shocks. The performance of the gauge during the field trial is also described. The conditioning period provides an excellent reference point to validate the quality of the co-located pressure and temperature values reported by the PT gauge installed at the toe of the well. The gauge temperature and pressure readings are compared to surface readings and subsurface saturated steam conditions. Temperature and pressure readings at the toe of the well during the production phase are analyzed and compared to intake pump pressure measured using a reputable, earlier-generation, optical PT gauge.
The glass Cane PT gauge provides improved reliability and accuracy because of the novel rigid internal structure of the device that preserves the slimline 1/4-inch external diameter. The increased accuracy of the measurements enables operations at a lower subcool, thus increasing production while lowering cSOR. The increased thermal and pressure range allows short bursts of extreme-high-pressure fluctuations and operation in cyclic steam stimulation (CSS) and other thermal applications.