ABSTRACT
The reopening pressure, i.e. the pressure applied on borehole wall at fracture opening, is clearly detected from variation of circumferential strain on the borehole wall in sleeve fracturing. The detected pressure allows us to estimate magnitude of the maximum horizontal stress. At the initial stage of pressurization, the circumferential strain increases linearly with the pressure applied on the borehole wall. However, drastic change appears in increasing rate of the circumferential strain once the fracture begins to open, and from such a change, the reopening pressure can be detected. To demonstrate this idea, we developed a transducer for the measurement of the circumferential strain. The transducer is designed so small to be installed on surface of a packer element for a borehole of 76 mm in diameter. The transducers of twelve are placed on the packer surface in the circumferential direction so that the circumferential strain can be measured on the borehole wall at intervals of 30°.
