Neutron-Gamma Density Through Normalized Inelastic Ratio

摘要

Systems, methods, and devices for determining neutron-gamma density (NGD) measurement of a subterranean formation that is accurate in both liquid- and gas-filled formations are provided. For example, a downhole tool for obtaining such an NGD measurement may include a neutron generator, neutron detector, two gamma-ray detectors, and data processing circuitry. Neutron generator may emit neutrons into a formation, causing a fast neutron cloud to form. Neutron detector may detect a count of neutrons representing the extent of the neutron cloud. Gamma-ray detectors may detect counts of inelastic gamma-rays caused by neutrons that inelastically scatter off the formation. Since the extent of the fast neutron cloud may vary depending on whether the formation is liquid- or gas-filled, data processing circuitry may determine the density of the formation based at least in part on the counts of inelastic gamma-rays normalized to the count of neutrons.

主权项

1. A downhole tool comprising:
a neutron generator configured to emit neutrons into a subterranean formation; a neutron detector configured to detect a count of neutrons that return to the downhole tool after interacting with the subterranean formation; a plurality of gamma-ray detectors configured to detect counts of inelastic gamma-rays that form when neutrons are inelastically scattered by the subterranean formation; and data processing circuitry configured to determine a density of the subterranean formation based at least in part on the counts of inelastic gamma-rays normalized to the count of neutrons.