A new type of confining vessel has been developed to undertake high-pressure, flow test experiments, at simulated lithospheric stress conditions. Confining pressure is generated by the uniaxial compression of a rubber medium, which leads to the term Rubber-Confining Pressure vessel ‰ (R-CPV) to describe this system. The pressure vessel is composed of an outside cylinder, an inside cylinder to hold the sample, rubber to generate the confining pressure and facilitate sample sealing, a hollow piston for rubber compression, and an outside piston for hollow piston compression and maintaining inner fluid pressure.
The fundamental principle of the R-CPV apparatus is the establishment of confining pressures which utilizes rubber elasticity to generate isotropic pressure. The rubber is bound to the sample and hollow piston only compresses the rubber. Pressure of compression is converted to confining pressure, which correspondingly affects the sample. The outside piston has holes for fluid inflow and outflow.
Testing of the R-CPV vessel, using butadiene rubber, has shown it can generate over 100 MPa maximum confining pressure, with 245kN pressing capacity, and facilitate permeability measurements under a range of high confining pressures. For example, preliminary results of flow test experiments for tension cracks in Inada granite, show hydraulic permeability rapidly decreases at <50 MPa confining pressure, whilst the apparent decrease in hydraulic permeability declines more gently at conditions of >50 MPa. Our experiments show that the new R-CPV apparatus has great potential for better understanding a wide range of geological issues, and likely industrial applications, as it can accommodate permeability-flow testing under a wide range of high confining pressure conditions.
