Downhole Evaluation with Neutron Activation Measurement

摘要

Neutron activation measurement techniques may be used to evaluate various properties of a subterranean well structure. In an example implementation, a logging tool can be positioned within a wellbore, such that neutrons generated by a neutron source are directed towards well structure. In response to the neutrons, the well structure emits gamma rays. A portion of the gamma rays can be detected by a gamma detector. To enhance the well structure's response to neutron activation, the well structure can be constructed of materials that include one or more doping materials. The inclusion of these doping materials can increase the number of gamma rays that are emitted when neutrons are directed into the well structure, and these emitted gamma rays can be more easily identified based on their energy level.

主权项

1. A method for monitoring a subterranean well structure at least partially composed of a first doping material comprising:
moving a logging tool in the subterranean well structure; emitting neutrons towards the subterranean well structure at least partially composed of a first doping material; detecting and counting activation gamma rays emitted by the subterranean well structure in response to the neutrons; determining a ratio between the counted number of detected activation gamma rays and an expected number of detected activation gamma rays; and determining information corresponding to a characteristic of the well structure based on the ratio; wherein the logging tool is moved relative to the subterranean well structure at a velocity that depends on: a distance between a neutron source and a gamma ray detector of the logging tool; and a gamma decay half-life corresponding to the first doping material.