Interpretation of the tilt response of two tiltmeters to water injection into a tar sands formation

Abstract

Near-surface tilt associated with fracture growth caused by water injection into a tar sands formation during an 18-day period was monitored by two biaxial mercury-level borehole tiltmeters. A nonlinear inversion method has been used to determine the fracture dimensions and position of its centre for five data groups from within that time. The inversion is limited by having data from only two tiltmeters, and a horizontal rectangular fracture must be assumed. The fracture expands rapidly initially, and more slowly as time progresses. The area of the fracture increases from approximately 5000 to about 240 000 m2 during the 18 days of injection and its centre migrates approximately 50 m. Key words : tiltmeters, tilt response, enhancement monitoring.