Abstract: An apparatus and a method for determining characteristics of earth formations traversed by a borehole that compensates the mudcake and standoff effects with fewer than usual detectors. The apparatus includes an radiation source effective to generate first and, spatially as well as temporally separate, second X-rays for irradiating earth formations from first and second entrance angles, one or more X-ray detectors capable of generating a first and a second signal indicative of the intensity of the first and second X-rays returned from earth formations to the detectors and a housing accommodating the radiation source and the detectors.

Abstract: A method for a pulsed gamma-gamma density tool to simultaneously compensate for interactions due to the photoelectric effect and density variations caused by standoff enables a more precise determination of bulk formation density. This method includes the steps of providing a source of energetic particles and directing those energetic particles at a formation having a known photoelectric factor and electron density and capturing one or more photons either emitted or deflected from the formation either a first detector or a second detector. The first detector is spaced a first distance from the source, the second detector is spaced a second distance from the detector and a third distance separates the first detector from the second detector.

Abstract: A more precise determination of bulk formation density is attainable using a pulsed ?-? density tool and simultaneously compensating for interactions due to photoelectric effect and density variations caused by standoff. A source directs energetic particles at a formation having a known photoelectric factor and electron density. One or more photons either emitted or deflected from the formation are captured at a first or second detector, respectively spaced at first and second distances from the source, and separated from each other by a third distance. First and second total energies of the photons respectively striking the first and second detectors are measured during a time interval. A first filter is disposed between the first detector and formation effective to cause Pe response to match standoff influence, thereby compensating for both effects simultaneously. In some embodiments, a second filter is provided between the second detector and formation.

Abstract: An apparatus and a method for determining characteristics of earth formations traversed by a borehole that compensates the mudcake and standoff effects with fewer than usual detectors. The apparatus includes an radiation source effective to generate first and, spatially as well as temporally separate, second X-rays for irradiating earth formations from first and second entrance angles, one or more X-ray detectors capable of generating a first and a second signal indicative of the intensity of the first and second X-rays returned from earth formations to the detectors and a housing accommodating the radiation source and the detectors.

Abstract: A logging tool includes an elongated body housing a neutron source and at least one neutron detector positioned along one side of the neutron source. Some embodiments of the logging tool include at least one gamma ray detector longitudinally separated from and to one end of the neutron source, and may be used to make simultaneous gamma ray and neutron logging measurements. In some embodiments, the logging tool also includes a (n, 2n)-neutron shield positioned to one end of the neutron detector, longitudinally between the neutron detector and the neutron source.

Abstract: The invention concerns a neutron measurement method for determining porosity of an earth formation surrounding a borehole comprising: conveying a tool along said borehole, wherein said tool comprises a source of neutron radiation and at least one detector axially spaced from said source; generating measured detector response for said at least one detector that is indicative of neutron radiation from said source interacting with said earth formations; operating said measured detector response with a predetermined mathematical equation and thereby obtaining corrected detector response that is independent of the density of said earth formation; and determining porosity of the earth formation surrounding the borehole from said corrected detector response. The invention also relates to a system implementing said method.

Abstract: A logging tool includes an elongated body housing a neutron source and at least one neutron detector positioned along one side of the neutron source. Some embodiments of the logging tool include at least one gamma ray detector longitudinally separated from and to one end of the neutron source, and may be used to make simultaneous gamma ray and neutron logging measurements. In some embodiments, the logging tool also includes a (n, 2n)-neutron shield positioned to one end of the neutron detector, longitudinally between the neutron detector and the neutron source.

Abstract: A gamma-gamma sonde for use in determining the bulk density of an earth formation adjacent a borehole comprises a source of gamma radiation and three attenuation-type gamma ray detectors DN, DI and DF spaced apart from the source, respectively, at successively greater distances. The count rate of each detector is converted into an apparent formation density .rho. based on data derived from calibration of the sonde in calibration media having known uniform density, thereby to obtain apparent formation densities .rho..sub.F, .rho..sub.I and .rho..sub.N. The ratio(.rho..sub.F -.rho..sub.I) to (.rho..sub.F -.rho..sub.N)is substantially independent of mudcake density and provides an estimate of the mudcake thickness. The calibration data involving mudcakes of known density and thickness enable the use of the mudcake thickness estimate to determine the value of k in the algorithm.rho..sub.apparent =.rho..sub.F +k(.rho..sub.F -.rho..sub.N),from which formation density is determined.