A method of determining downhole formation oil saturation and three-phase holdup is described. The method includes lowering a pulsed-neutron logging tool downhole with a near detector and a far detector. The method further includes measuring a carbon to oxygen ratio from the near detector, measuring a carbon to oxygen ratio from the far detector, measuring a ratio of inelastic count rates, and plotting the measured ratios in a prismatic grid. The method further includes visualizing the fluid volumetrics around the pulsed-neutron logging tool.

A method for obtaining a gas saturation value of a subterrain formation involves a tool having multiple dual-function detectors that detect neutrons and gamma rays. The method includes steps of emitting neutrons into the formation, detecting neutrons and gamma ray signals form the formation using the detectors, determining formation parameters including the formation type and formation porosity, and further determining parameters such as the ratio of thermal neutron count rates from at least two of three detectors, the ratio of capture gamma count rates from at least two of three detectors, and calculating the real-time gas saturation value using the determined parameters.

Methods and related systems are described for gamma-ray detection. A gamma-ray detector is made depending on its properties and how those properties are affected by the data analysis. Desirable properties for a downhole detector include; high temperature operation, reliable/robust packaging, good resolution, high countrate capability, high density, high Z, low radioactive background, low neutron cross-section, high light output, single decay time, efficiency, linearity, size availability, etc. Since no single detector has the optimum of all these properties, a downhole tool design preferably picks the best combination of these in existing detectors, which will optimize the performance of the measurement in the required environment and live with the remaining non-optimum properties. A preferable detector choice is one where the required measurement precision (logging speed) is obtained for all of the required inelastic elements and/or minimization of unwanted background signals that complicate the data analysis.

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.

Systems, methods, and devices for determining a 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, a neutron detector, two gamma-ray detectors, and data processing circuitry. The neutron generator may emit neutrons into a formation, causing a fast neutron cloud to form. The neutron detector may detect a count of neutrons representing the extent of the neutron cloud. The 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, the 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.

Scale identifier systems and methods for generating a log of scale type and location in subterranean formations, and, more particularly, in wellbore tubing are provided. A method for scale identification may be provided. The method may comprise providing a first logging tool comprising a tool body, a neutron source coupled to the tool body, and detectors coupled to the tool body; providing a second logging tool for measuring deviations in inner diameter of a tubing in a wellbore; placing the first logging tool and the second logging tool into the wellbore; logging the interior of the tubing with the first logging tool and the second logging tool to generate data; and generating a log of scale location and type from the data.

Methods and related systems are described for gamma-ray detection. A gamma-ray detector is made depending on its properties and how those properties are affected by the data analysis. Desirable properties for a downhole detector include; high temperature operation, reliable/robust packaging, good resolution, high countrate capability, high density, high Z, low radioactive background, low neutron cross-section, high light output, single decay time, efficiency, linearity, size availability, etc. Since no single detector has the optimum of all these properties, a downhole tool design preferably picks the best combination of these in existing detectors, which will optimize the performance of the measurement in the required environment and live with the remaining non-optimum properties. A preferable detector choice is one where the required measurement precision (logging speed) is obtained for all of the required inelastic elements and/or minimization of unwanted background signals that complicate the data analysis.

A downhole tool is provided with a neutron generator configured to emit neutrons into a geological formation. The downhole tool includes one or more neutron detectors configured to detect neutrons that return to the downhole tool after interacting with the geological formation. The downhole tool also includes one or more gamma ray detectors configured to detect gamma rays from the geological formation that form when neutrons are inelastically scattered by the geological formation. Measurements from a combination of detectors of at least one of the one or more neutron detectors and at least one of the one or more gamma ray detectors are used to determine formation density. A first formation density determined using a first combination of detectors is used to compensate a second formation density determined using a second combination of detectors.

The present disclosure is intended to overcome the problem of hydrogen contamination of the density signal. The approach is to compute the neutron capture portion of the total gamma ray counts and subtract it from the total counts resulting in a pure inelastic gamma ray measurement.

A method for detecting the presence of an insulation gas in a housing. The method may include setting a high voltage power supply to a first voltage, wherein the first voltage flows through a ladder disposed in a pulsed neutron logging tool. The method may further include taking one or more measurements of a current flowing through the ladder and comparing the one or more measurements of the current to a threshold.