Injection testing in packer isolated intervals is a single borehole technique widely used to characterise moderate to low hydraulic conductivity [K] rock mass in mining projects. The technique is easy to piggy-back onto resource and geotechnical drilling programmes to save time and cost.
The principal advantage of packer testing is the ability to investigate rock mass hydraulic properties in narrow diameter boreholes to depths of more than 1000m. The test data allow estimation of vertical distribution of rock mass hydraulic conductivity (K), which is often needed to inform numerical groundwater models to predict water inflow and pore pressure distribution around the mine.
Despite their widespread usage, there is a relatively poor understanding of the extent of tested rock mass, the effects of undertaking testing in cumulative overlapping (successive) intervals within a limited time-period, the effect of elastic storage on packer test results and the degree of borehole skin effect on the packer tests results.
The results of this paper demonstrate that the use of cumulative overlapping packer testing method (used following completion of borehole drilling) should be implemented with caution with a full understanding of the limitations demonstrated here. Cumulative testing provides a fast and effective method for ‘screening’ of boreholes, particularly in a low K environment. High importance is given to the test pressure approach and the equations used to estimate K.
The effects of borehole skin and rock mass storativity should also be carefully considered during both cumulative and concurrent packer injection testing, underlying the need for pumping tests to confirm and quantify these aspects.
