HydroMechanics of Fractured Rock

Removable Borehole Extensometer

EXTENSOMETER FUNCTIONALITY
The extensometer is mounted between the packers and lowered to depth in a wellbore. Pneumatic cylinders extend two carbide grippers, two meters apart, into the face of the borehole. The extensometer is disengaged from the frame, so it only responds to rock displacement. A registration system sets the extensometer within the range of the measurement device prior to testing, then it is released so the anchor points are independent of one another during testing. A high-resolution Linear Variable Differential Transformer (LVDT) measures the displacement of the anchor points. Invar is used in critical components of the extensometer to minimize the influence of temperature variation. Current field data suggests that the device is capable of detecting displacements on the order of 0.1 microns at depths of 100 meters.

SCHEMATIC OF EXTENSOMETERS