RECENT EXPERIENCE WITH EXTENDED LEAK-OFF TESTS FOR IN-SITU STRESS MEASUREMENTS IN AUSTRALIA

Abstract

The historical and theoretical backgrounds of standard and extended leak-off tests with respect to in-situ stress measurement are discussed and compared with hydraulic fracture stress measurement as practised in other industries. The relative advantages of extended leak-off tests compared with standard tests in this context are discussed and a case made for the extended test procedure. The diagnostics of pressure records obtained from extended leak-off tests are discussed in light of extensive experience obtained from hydraulic fracture stress measurement, with reference to a number of extended leak-off tests conducted in Australia. A conclusion is reached that extended leak-off tests can potentially provide data of quality comparable with that obtained from ideal hydraulic fracture stress measurement, allowing resolution of the in-situ stress field with reasonable reliability in many cases. The results of some Australian extended leak-off tests are discussed and contrasted with corresponding data obtained from standard leak-off tests. A trend is revealed from this data for extended leak-off tests to produce a lower estimate of the minimum stress magnitude than standard leak-off tests.