Hydrofracturing technique has been developed and utilized for wells of oil-pumping and of collecting geothermal energy. Recently, the technique is also applied to measure geo-stresses. For these purpose, we have to investigate more throughly the relations among stress state, frac ture strength, pore-water pressure, peamiability of geomaterials and so on, In addition1 since the hydrofracture may occur at the point of the highest tensile stress, we have to investigate stress state of a bore hole and water pucker conditions when the hole is pressured.
In this researh, ' we intentively investigate the following items :
l)model test of hydra fracture and numerical simulation analysis of it
2)mechanism of hydrofracturing
3)transport phenomena of water and thermal energy through the fractured zone.
The following results are summarized.
1)model experiment : Specimens having a bore hale along the one of the center line were prepared, Under the tri-axial state of stresses, the specimens were hydrofractured by pressing oil into the bore hole, We measured the 3-D stress state, injected all pressure and acoustic emmission while pressuring the oil. We recognized the initiation of branch crack from the bore hole. Relations among oil pressure at the fracture initiation, progress of the fracture, 3-D state of stress state were investigated. The numerical simulation analysis for the model is under developing.
2)Hydrofractuning : Relations among fracture progress (crack gnawth), oil pressure variation and initial state of stress were not sufficiently clarified. The relations are now being investigated by numerical simulation using Boundary element Methods.
3)Transport phenomea : Already lots of research works have been done for the phenomena. These re suits are easily applied whenever the fracture surfaces are determined by 1) or 2). We are not so much interested in this topics.