Shigen-to-sozai, Vol.116, No.7, pp.636-641.
Evaluation of Shut-in Pressure by Fracture
Opening Displacement Measurement
Takashi TAKEHARA1, Tsatomu YAMAGUCHI1, Voshiaki MIZUTA2, Takashi NARITA1 and Harnynki ISHIHARA1
| 1. National Institute for Resources and Environment,
Onogawa, Tsukuba 305-8569 2. Department of Civil Engineering, Yamaguchi University, Tokiwadai, Ube 755-8611 |
| 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 coaxial
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 coaxial pipes. This shut-in pressure estimated from the metal-seal packer agreed well with those from the Muskat method and Haynshi & Haimson method. |
| KEY WORDS: Hydraulic Fracturing, Fracture Aperture, Shut-in Pressure, Double Packer, Rubber-Seal Packer, Metal-Seal Packer |