Volume 30, Issue 3 (May 2007)
Removable Borehole Extensometers for Measuring Axial Displacements During Well Tests
Fractures in rock hold important stores of water and petroleum, and slight changes in fracture aperture accompanying drawdown from pumping wells play a key role in recovering these resources. Two removable borehole extensometers were designed to measure small displacements in order to improve the characterization of fractured rock aquifers using hydraulic well tests. The extensometers consist of four major components: (1) a pair of anchors, (2) a temperature-compensated reference rod, (3) a registration system, and (4) a displacement transducer. One extensometer uses an axial reference rod with multiple, low-profile anchors, whereas another uses an offset reference rod with a single pair of anchors. Both designs can be readily mobilized and are capable of resolving submicron displacements in boreholes.