Near-surface tilt response to steam injection into a tar sands formation

Two biaxial mercury-level borehole tiltmeters located at moderate depth (20 m) and 91 m horizontally distant from the injection well have been used to monitor the effects of a fast hydraulic fracture and subsequent steam injection in a tar sands formation at a depth of 230 m. Tilt vectors are determined for the maximum tilts during the fracture, and the long-term tilt migration associated with the steam-injection process is monitored. The tilt associated with the fast fracture is of the order of 1–2 μrad, and the long-term tilt increased as much as 240 μrad over the 500 day monitoring period, and appeared to approach a limit. The long-term tilt migration generally follows the same orientation as the initial tilt due to the fast fracture.