| abstract |
Disclosed is a well logging method and apparatus for obtaining impulse response of a formation traversed by a bore hole by means of correlation techniques. Use is made of a source of radiant energy and of a control element for said source to produce a substantially random or pseudorandom sequence of discrete bursts of radiant energy from the source to cause interactions of these bursts with the formation whereby characteristic radiations of interactions are produced. A detector is provided which is responsive to these radiations to produce corresponding signals. In one embodiment of my invention the impulse response, expressed by a function h(t), is obtained by crosscorrelating signals produced by the detector with signals representing the bursts of radiant energy from the source. In another embodiment the impulse response h(t) of the formation is obtained by autocorrelating signals produced by the detector. In another embodiment of my invention the outputs of two detectors, differently spaced from a source of radiant energy, are crosscorrelated. Using the function h(t), valuable information regarding physical properties of the formation may be obtained. The source of radiant energy may be a source of energetic neutrons, particularly of the deuterium-tritium type, or a source of gamma radiation or of microwaves, or a source of any other form of radiant energy. |