Abstract: The nature of hydrogenous fluids filling the pore spaces in formations surrounding a well bore are determined by irradiating the formation with bursts of high energy neutrons and using the ratio of time-dependent parameters related to the decay of epithermal neutron populations above two different energy levels to provide values indicative of the kind of fluid present, independent of porosity. The measurement above the higher of these energy levels, approximately 0.4 eV, indicates the existence of hydrogenous fluid, water and hydrocarbons, in the formations; the lower threshold measurement, above approximately 0.15 eV, is indicative of the structure of the molecule in which the hydrogen molecule is bound and the porosity. A pulsed neutron generator in a sonde irradiates the formations with 14 meV neutrons and a pair of detectors, one shielded by cadmium to establish the 0.4 eV threshold energy level and the other, shielded by gadolinium to establish the 0.

Abstract: The porosity of an earth formation is derived in a plused neutron logging tool by use of a directionalized and borehole-shielded eptithermal neutron detector array and by processing detector count rate measurements of the epithermal neutron die-away curve in accordance with a multi-parameter fit to obtain as one parameter the epithermal neutron decay time of the formation and as a second parameter an indication of detector standoff (environmental) effects. The multi-parameter fitting procedure separates the formation and standoff effects on the measured count vs time curve, and yields a decay time measurement that is primarily representative of formation porosity and substantially free of environmental effects. To enhance count rate statistics, the neutron source and one or more of the epithermal neutron detector may be located at the same depth in the borehole. The neutron burst centroid is monitored an used to define a fiducial window for processing the die-way curve data.

Abstract: A method and apparatus for determining the contents of a borehole traversing a subterranean formation is provided. In the method, a well-logging sonde is used to bombard the contents of a borehole and the formation with fast neutrons. An early capture spectrum signal is generated to reflect the composition of the formation and the contents of the borehole. A late capture spectrum signal is generated to reflect the composition of the formation. The early capture spectrum signal is compared with the late capture spectrum signal to derive an output signal representative of the spectral composition of the contents of the borehole.Additionally provided are improved methods and apparatus for determining the contents of a subterranean formation. An inelastic spectrum signal is generated to reflect the detailed combined composition of the formation and contents of the borehole.

Abstract: In the illustrative embodiments of the invention disclosed, the composition of an earth formation is investigated by repetitively irradiating the formation with bursts of fast neutrons and generating an energy spectrum of the gamma rays resulting from the inelastic scattering of such neutrons by nuclei of the formation. The inelastic scattering gamma ray spectrum is analyzed by comparing it with a composite spectrum, made up of standard spectra of constituents postulated to comprise the formation, to determine the proportions in the formation of the postulated constituents. A background energy spectrum is generated from gamma rays detected during periods between neutron bursts and is utilized to provide one or more standard background spectra for use in the analysis of the inelastic scattering gamma ray spectra. The standard background spectrum or spectra are preferably updated on a repetitive basis to reflect the current background component in the detected inelastic scattering gamma ray spectrum.

Abstract: Methods and apparatus are disclosed for selecting, among input signals, those which are time-spaced from each other by more than a predetermined time interval. Clock pulses are continuously applied to a pulse counter, and a predetermined count signal is produced each time the counter reaches a predetermined count. The counter is reset upon occurrence of either an input signal or a predetermined count signal. The order of occurrence of the input signals and of the predetermined count signals is memorized, and a validation signal is produced for each input signal which is directly preceded and followed by a predetermined count signal. Signals distorted by pile-up effect can thus be rejected.

Abstract: In the particular embodiments described, a telemetering system for well logging receives and temporarily stores binary-coded parallel data in a downhole memory unit and continuously interrogates and transmits the stored data to the surface at fixed rate in binary-coded serial format. The system thus accommodates high instantaneous data-generation rates, such as are encountered, for example, in gamma ray spectroscopy tools, without loss of information on the cable. The stored data is compacted, by suppressing leading zeros in data words, prior to application to the cable. This affords faster memory read-out and reduces cable transmission time. The data word format and signal format utilized on the cable provide low error-rate data flow to the surface, as well as facilitating the maintenance of synchronous operation between downhole and uphole functions.

Abstract: In the particular embodiments of the invention described, the formation surrounding a cased borehole is irradiated with bursts of high-energy neutrons and the resulting neutron population in the formation is observed at two spaced locations along the borehole. A neutron absorption characteristic of the formation is determined from the population measurement at one location, and a ratio of the population measurements at the two locations, suitably corrected for background radiation, is formed. Preferably, the neutron population measurements at both locations are made during measurement periods which are controlled as a function of the measured value of the neutron characteristic. Cross plots of the ratio and the neutron characteristic values thus derived afford apparent values of formation porosity and formation water salinity, from which water saturation values can be estimated.