2016 年 57 巻 2 号 p. 112-118
The evaluation of hydraulic constants is generally one of the main components of reservoir engineering projects such as the development of radioactive waste disposal sites or the construction of underground CO2 storage. In the example presented here, flow pump experiments were conducted for the Horonobe mudstone to evaluate specific storage and hydraulic conductivity. The flow pump experiments were conducted with an effective confining pressure that gradually increased from 2 to 10 or 12 MPa, followed by a subsequent reduction to the initial value. The hydraulic conductivity in all cases was observed to decrease with increasing effective confining pressure in the specimens, and it did not recover to its initial value after unloading. In contrast, specific storage was observed to decrease in some specimens with increasing effective confining pressure; although this tendency was not significant in comparison to the trend observed concerning hydraulic conductivity. We therefore used theoretical analysis to calculate hydraulic constants and evaluate error ranges based on the nonlinear least-squares method. The error range value of specific storage is proposed to reduce with larger flow rates under the same confining pressures. The experimental results showed an almost linear pressure distribution from the upstream to downstream surfaces, and also showed a gradual increase in differential pressure with time in the flow pump method. Taking error ranges into account, the flow pump method is probably an easy approach for evaluating the specific storage of mudstone compared with other means of investigation that are currently available.
