METHOD AND APPARATUS FOR SUBSURFACE FORMATION EVALUATION

摘要

A measurement while drilling nuclear tool adapted to be coupled in the drill string to make formation evaluations and methods of using are described. A neutron source (58) is positioned on the cylindrical axis of the tool while a connected gamma ray source (47) is eccentered against an interior side of the cylindrical tool. Both sources can be axially removed from the tool along its interior. Novel source-detector configurations are provided in order to accommodate the constraints of the MWD environment. Gamma ray transparent windows (50, 51) are provided through both the drill collar and an external fluid excluder (stabilizer) (21) at the positions of the gamma ray source and scintillator detectors. Neutron detectors may be of two different types at the same spacing from the source. Corrections are made for microphonic noise that arises while drilling and for natural gamma ray background. A drilling fluid density determination is made and is utilized to compensate for "borehole" or "standoff" effects.