Abstract: Downhole measuring apparatus includes a gamma radiation source and at least two pairs of radiation detectors carried by a housing so that radiation may be emitted from the source and scattered by the environment of the housing and detected by the detectors. Each pair of detectors is arranged so that its detectors are positioned symmetrically on opposite sides of the longitudinal axis of the housing, and each pair of detectors, in combination with the radiation source, forms a different geometrical configuration so that, in general, the radiation counts obtained by the different pairs of detectors will not be redundant. The output signals from the detectors may be processed to provide data signals indicative of the radiation counts experienced by the detectors, and which may then be used to simultaneously obtain values for two or more downhole parameters. The addition of each new, independent pair of detectors permits the simultaneous solution of an additional downhole parameter.

Abstract: A method of calibrating a radiation detector, positioned in apparatus including a source of gamma radiation such that the detector may sense radiation from the environment of the apparatus due to radiation emitted by the source and scattered by the environment, includes utilizing test environments including formations of known bulk densities. The apparatus may be positioned within the test environments at different distances from the surfaces of the formations. Count rates of the detector are compared to the formation bulk densities for the distances of the apparatus from the formation surfaces to calibrate the detector relative to the radiation source.

Abstract: A gamma radiation logging system utilizes a single fixed gamma ray source spaced from a plurality of detector means arranged in banks so that the readings of the detectors can be utilized individually and in combination to derive the formation density, mud density and borehole diameter. The subject invention is capable of making the above determinations in a while-drilling condition without requiring physical contact with the formation nor making assumptions regarding composition of the formation or requiring further information from secondary sources. Each detector generates an output signal proportional to the photons reaching the detector with the signals being used to determine formation density, mud density and borehole diameter individually and collectively.

Abstract: When surveying a borehole using an instrument responsive to the earth's magnetic field, a length of non-magnetic drill collar is necessary to house means for measuring the magnetic field in the borehole perpendicular to the direction of the borehole axis. The instrument determines the inclination angle and the highside angle from the gravitation measurements, with these measurements and the magnetic measurements, the azimuth angle is determined. Using the method of this invention a minimum length of non-magnetic material necessary for an accurate measurement may be calculated and used.

Abstract: .[.When surveying a borehole using an instrument responsive to the earth's magnetic field, a length of non-magnetic drill collar is necessary to house means for measuring the magnetic field in the borehole perpendicular to the direction of the borehole axis. The instrument determines the inclination angle and the highside angle from the gravitation measurements, with these measurements and the magnetic measurements, the azimuth angle is determined. Using the method of this invention a minimum length of non-magnetic material necessary for an accurate measurement may be calculated and used..]. .Iadd.Disclosed are method and apparatus for surveying a borehole including use of a survey instrument for making gravitational measurements from which the inclination and highside angles of the instrument may be determined.