Abstract: Through analysis on an effective detection space of a gamma detector, a one-dimensional equivalent longitudinal contribution coefficient (varying with a distance between a formation and the detector) of a natural gamma-ray flux received by the gamma detector under the condition that the formation and a wellbore are orthogonal is obtained in the effective detection space, and then a corresponding function expression is given by fitting. An integral of a gamma-ray flux received by the detector under the condition of a deviated well is converted into a one-dimensional equivalent integral problem under the condition of a straight well, so as to achieve the fast forward of natural gamma-ray logging of the formation under the conditions of highly-deviated and horizontal wells. This simplified fast forward algorithm can replace a gamma forward method of spherical spatial-division integrals in parallel sedimentary formations, reduce a space-time complexity of algorithms, and improve a calculation efficiency.

Abstract: Through analysis on an effective detection space of a gamma detector, a one-dimensional equivalent longitudinal contribution coefficient (varying with a distance between a formation and the detector) of a natural gamma-ray flux received by the gamma detector under the condition that the formation and a wellbore are orthogonal is obtained in the effective detection space, and then a corresponding function expression is given by fitting. An integral of a gamma-ray flux received by the detector under the condition of a deviated well is converted into a one-dimensional equivalent integral problem under the condition of a straight well, so as to achieve the fast forward of natural gamma-ray logging of the formation under the conditions of highly-deviated and horizontal wells. This simplified fast forward algorithm can replace a gamma forward method of spherical spatial-division integrals in parallel sedimentary formations, reduce a space-time complexity of algorithms, and improve a calculation efficiency.