Focussed packer testing: a structured approach to save time and improve results

Abstract

AbstractThe idea of ‘focussed’ packer testing is to focus the cost and effort of packer testing on the regions of greatest concern. The effect is to reduce the amount of unnecessary testing and hence cut the cost of testing. It is based primarily on identifying the use of the collected data. In work concerned with the disposal of radioactive waste the prime use of the derived data is in numerical modelling. For most modelling purposes data from highly transmissive rock are of more importance than those from low permeability regions. It is proposed that the testing should be structured so that there is a smooth increase of value and locational accuracy from the lower measurement limit up to the maximum.Two basic methods of test and data structuring are proposed. These are based on a specific test management procedure termed ‘log-linear structuring’ and the ‘active packer string’. These two techniques have different effects on costs and derived data quality.In procedural management, the technique described as ‘log-linear structuring’ has a straightforward effect on the ‘value-accuracy’ of the data set. It reduces the accuracy and reliability of the derived data progressively as its value decreases. It does not change the overall form of the data set. Its effect on programme costs is only in the order of a 20 to 30% reduction.The use of the ‘active packer string’ to structure ‘locational accuracy’ changes the form of the overall data set. There are subtle controls on the form of the data set produced by the ability to set not only sample size but also thresholds for improved quality of data. If an ‘active packer string’ is used to reduce costs then cost savings of 50% or more are possible whilst maintaining data quality.In order to carry out ‘focussed’ packer testing it is necessary to: (i)have foreknowledge of the use of the data and the rock to be tested;(ii)be able to simulate the effect of ‘focussed’ testing in a particular rock and borehole environment;(iii)be able to analyse the results instantly in the field;(iv)have access to an ‘active packer string’ for most effective test design and control.A set of results from a field test in Sweden shows the form of data which is obtained using an ‘active packer string’, the form of the overlapping and a time saving of about 50%.