A combination of microseismic and surface deformation monitoring with an array of tiltmeters was used to monitor the warm-up phase of a SAGD well pair. A sequence of microseismic events was recorded with signal characteristics suggesting deformation associated with thermal expansion of the wellbore, in addition to events apparently associated with induced fracturing in the reservoir. Integration of the microseismic data with volumetric strain, inverted from the measured surface deformation, indicates a discrete deforming region near the toe of the well. The volumetric strain also shows another region near the heel of the well, although the area is too far from the microseismic observation well for any associated microseismicity to be recorded. The central portion of the well pair did not have significant deformation, indicating poor steam conformance during this warm-up phase. A comparison of the temporal response of the microseismic deformation with the surface uplift, suggests a lag between periods of accelerated seismic deformation followed by an associated period of accelerated uplift a few days later. This timing suggests the creation of a fracture network and related seismic deformation, which then fills with steam and starts to expand over a period of a few days. In a related paper9, stress changes associated with the volumetric strain are used to examine potential geomechanical failure zones that match the observed locations of microseisms. Together the volumetric strain, computed stress changes, and failure zones could be used to calibrate a geomechanically linked reservoir simulator.
Dusseault, Maurice B. (Faculties of Engineering and Science, Departments of Mineral Engineering and Physics, University of Alberta) | Nyland, Edo (Faculties of Engineering and Science, Departments of Mineral Engineering and Physics, University of Alberta)