Rock strength predictions from wireline logs

Abstract Small diameter wireline logging tools have been run in cored boreholes drilled through U.K. Coal Measures strata. Their responses are compared with continuous strength curves generated from point-load tests carried out at small regular intervals over long lengths of rock core. Relationships between individual log responses and the point load strength are examined using a log blocking procedure and the effects of combining log responses to predict the rock strength are also discussed. The neutron—neutron log is shown to be a useful strength predictor, being generally superior to all other commonly used logs, including the interval transit time sonic log.