A New Facility For The Investigation Of Nuclear Logging Tools And Their Calibration

An experimental programme is being undertaken at Winfrith, funded by the Department of Energy under the sponsorship of the Offshore Supplies Office to investigate improved techniques for the design of test pits and the calibration of nuclear logging tools. One of the main objectives of this programme is to demonstrate the capabilities of computer modeling for the characterisation of test pits and the calculation of departure curves. The computations will be executed with a suite of radiation transport ties which has been developed for the shielding of nuclear plant. With the very detailed treatment of the geometry afforded by these codes, the accuracy of prediction is determined by the uncertainties in the nuclear cross-section data. Nuclear data bases have been established by benchmark experiments over many years in support of the UK reactor programme and the response of logging tools can now be predicted with a high degree of accuracy - provided that the physical and nuclear characteristics of the environment are well known. Studies carried out to date have identified uncertainties in the composition of natural rocks as a major source of error in the computer modeling of nuclear logging tools in bore hole environments. The elimination, or at least reduction, of this area of uncertainty requires a new standard of test pit characterisation. Having achieved a sufficiently well defined system, departures from the test conditions can readily be examined by theoretical experiments on the computer and their validity can be checked by measurements made on a limited number of representative cases. The exploitation of this approach for log interpretation would be accomplished by iterative calculations between the test formation and postulated field environments.