In this paper, a newly developed double packer was introduced. In hydraulic fracturing operation, an opening and closing behavior of a fracture was related to in-situ stress state. A purpose of the new packer was to measure the fracture opening directly. The new packer consisted of two co-axial pipes that move independently. As sealing elements were fixed to each of two pipes, fracture opening could be measure by relative displacements of two co-axial pipes. Two types of sealing elements were examined. One was a rubber and the other was lead. The former was named rubber-seal packer, and the latter is named metal-seal packer.
A conventional double packer, the rubber-seal packer and the metal-seal packer were used in the Kamioka mine in 1998. In this mine, a hydraulic fracturing experiment in order to estimate in-situ stress was done using a borehole that was drilled horizontally from a gallery in 1996. The newly developed packers were used to re-open the pre-existed artificial fracture.
The result of the metal-seal packer experiments showed that relative displacements of two co-axial pipes had a good correlation with the wall expansion that was measured at vicinity of the borehole. It became clear that the metal-seal packer was possible to measure the fracture aperture directly. The shut-in pressure, that is thought to be equivalent to a magnitude of normal stress component, was estimated from the relative displacements of two co-axial pipes. This shut-in pressure estimated from the metal-seal packer agreed well with those from the Muskat method and Hayashi & Haimson method.