Method for measuring subterranean formation density using a neutron generator

摘要

A method for determining a bulk formation density using a neutron generator includes detected secondary gamma rays and evaluating the detected gamma rays according to pre-determined selection criteria. Selected gamma rays are then used to compute the formation density. The selection criteria may include, for example, a time delay between the detection of a neutron and an associated particle and/or a direction of propagation of the neutron.

主权项

1. A method for measuring a formation density of a subterranean formation, the method comprising:
(a) generating neutrons in a subterranean borehole using an accelerator based neutron generator, said generated neutrons being emitted into a surrounding borehole environment; (b) detecting secondary gamma rays in the subterranean borehole, the secondary gamma rays being generated by an interaction between the neutrons generated in (a) and the surrounding borehole environment, and detecting neutrons in the subterranean borehole, the neutrons returning after being emitted into the surrounding borehole environment and the neutrons representing an azimuthally average neutron count; (c) causing a processor to identify certain ones of the secondary gamma rays detected in (b) based upon predetermined selection criteria identifying the secondary gamma rays as resulting from a neutron interacting with an azimuthally specific part of the formation less than a 360 degree azimuthal angle around the formation; and (d) causing a processor to process the gamma rays identified in (c) and the neutrons generated in (b) to compute a formation density of the subterranean formation.