In-situ flow testing of borehole plugs

Abstract

A cement borehole plug and a crushed tuff/bentonite clay mixture borehole plug were tested insitu in highly welded tuff. The hydraulic performance of the cement plug was evaluated through steady-state and transient hydraulic tests with a hydraulic conductivity in the range of 10⁻¹⁰ cm/s. A crushed tuff/bentonite mixture plug was tested through a steady-state flow test with a measured hydraulic conductivity of 10⁻⁹ cm/s. The plug was installed in a fractured borehole which was grouted to reduce the overall rockmass permeability. Installation procedures were evaluated in the laboratory prior to field installation. Installation of the cement seal with a bailer indicated seal degradation with water present in the borehole. Degradation appeared as piping, both internal and along the interface, and mixing of the cement with the water. Tests on the mixture seal indicated the need for homogeneous placement and adequate compaction to resist internal water piping and channelling.