抄録
The Minami-Kanto Gas Field yields natural gas dissolved in brine. The reservoir consists of alternate thin layers of sandstone and mudstone. Production of the brine from the reservoir has caused surface subsidence. Part of the produced brine has been injected back underground to reduce the subsidence.
In this study, we developed a K0-consolidation/swelling testing apparatus to simulate the deformation of the reservoir in a laboratory. Experiments with the apparatus were carried out on 6 mudstone core specimens from the reservoir. The results were as follows: 1) The specimens deformed plastically. 2) Some specimens continued to deform in spite of the static stress conditions. These observations suggest that the behavior can be regarded as viscous deformation. 3) The axial-strain behavior observed for the period of 72 hours could be fit to a rheological model. Calculation based on the model suggested that the viscous deformation would almost terminate in 30 days. 4) Correlation between the axial effective stress and the axial strain could be fit to an elast-plastic constitutive model.
