| 摘要 |
<p>The present invention relates to a method for investigating a subsurface earth formation which is traversed by a borehole. The method comprises the steps of generating a population of high energy neutrons in the borehole and formation, detecting gamma rays resulting from interactions between the neutrons and bombarded nuclei in the formation, deriving electrical pulses which have amplitudes functionally corresponding to the detected gamma rays and, making a time-dependent selection of those of the pulses corresponding to those detected gamma rays resulting from inelastic scattering of the neutrons by the bombarded nuclei. In addition, the method further comprises the steps of deriving from the time-dependent selection, a first energy-dependent selection of those pulses corresponding to gamma rays attributable to inelastic scattering of the neutrons from carbon nuclei and deriving from the time-dependent selection a second energy-dependent selection of those pulses corresponding to gamma rays attributable to Inelastic scattering of the neutrons by oxygen nuclei. The method includes the step of deriving the ratio of a function of the first energy-dependent selection to the second energy-dependent selection, making a second timedependent selection of those of the pulse corresponding to those selected gamma rays resulting from capture of the neutrons of the bombarded nuclei, and finally recording the second time-dependent selection in correlation with the record of the ratio to obtain a measurement of the porosity of the formation.</p> |
