FIELD: physics.
SUBSTANCE: gamma-radiation is measured using a gamma-radiation measuring instrument in a well surrounded by the formation in order to determine properties of the formation by carrying out steps for: generating gamma-radiation using a gamma-radiation source mounted on the measuring instrument in a well; detecting gamma-radiation using one or more gamma-radiation detectors mounted on the measuring instrument; and calculating response of the measuring instrument in accordance with one or more properties of the formation in a plurality of spatial positions relative the measuring instrument using a direct model, which allows nonlinear relationships between one or more properties in the plurality of spatial positions and the corresponding response of the measuring instrument, wherein one or more properties for at least some the plurality of spatial positions of the formation are evaluated in accordance with the detected gamma-radiation.
EFFECT: providing an advantage in accuracy, versatility and simplicity with negligible losses in computation speed.
50 cl, 49 dwg
