Abstract: An interlock system for explosive operations includes an array of magnet sensors configured to engage an array of magnets in a magnetic key. The key may be selectively positioned to activate select sensors while the other remains deactivated. Various sequences of activated and deactivated sensors correspond to various states of the interlock system. One or more switches of the interlock system are set according the state of the system. Some states set the switches to disable any electrical signals from passing to the explosives. Other states set the switches to enable select signals to pass to the explosive or other tools. Explosive operations are enabled only in a particular predetermined state.

Abstract: An initiator circuit for a perforating gun includes a microprocessor structured to perform a circuit-startup algorithm comprising determining whether the circuit supply voltage is stable enough for operation and, if it is, or if a predetermined period of time has passed since powering up the circuit, sending a message indicating the circuit (and thus gun) is ready for operation. The sent message may be a communication uplink indicating an address of the circuit and its ready state or a short burst of pulses indicating the circuit's ready state.

Abstract: A stack of addressable perforating guns with preassigned addresses may be configured for operation by identifying any duplicate addresses in the stack and deduplicating the addresses by assigning new addresses to at least a subset of any guns having the same address until each gun in the stack has an address unique in the stack.

Abstract: An initiator circuit for a perforating gun includes a microprocessor structured to perform a circuit-startup algorithm comprising determining whether the circuit supply voltage is stable enough for operation and, if it is, or if a predetermined period of time has passed since powering up the circuit, sending a message indicating the circuit (and thus gun) is ready for operation. The sent message may be a communication uplink indicating an address of the circuit and its ready state or a short burst of pulses indicating the circuit's ready state.

Abstract: Various downhole logging tools and methods of using and making the same are disclosed. In one aspect a method evaluating cement bond quality in a well is provided. In a well with a particular casing/tubing configuration, waveforms of acoustic energy returning from the tubing and the casing with the tubing present are recorded. A frequency spectrum from the recorded waveforms is determined. Amplitudes of the returning acoustic energy at one or more preselected frequency(s) of interest of a range of frequencies at which the amplitudes are noticeably affected by cement bond quality for the particular casing/tubing configuration are determined. The determined amplitudes are compared with one or more baseline amplitudes to look for indications of cement bond quality. Other aspects involve time domain analysis.

Abstract: A caliper-arm-position sensor comprising a differential variable reluctance transducer (DVRT) and circuits to drive the DVRT with a substantially sinusoidal signal and to sample a signal at the DVRT once per drive-signal cycle at a predetermined position in the drive-signal cycle is disclosed.

Abstract: Various downhole logging tools and methods of using and making the same are disclosed. In one aspect a method evaluating cement bond quality in a well is provided. In a well with a particular casing/tubing configuration, waveforms of acoustic energy returning from the tubing and the casing with the tubing present are recorded. A frequency spectrum from the recorded waveforms is determined. Amplitudes of the returning acoustic energy at one or more preselected frequency(s) of interest of a range of frequencies at which the amplitudes are noticeably affected by cement bond quality for the particular casing/tubing configuration are determined. The determined amplitudes are compared with one or more baseline amplitudes to look for indications of cement bond quality. Other aspects involve time domain analysis.

Abstract: Various downhole logging tools and methods of using and making the same are disclosed. In one aspect a method evaluating cement bond quality in a well is provided. In a well with a particular casing/tubing configuration, waveforms of acoustic energy returning from the tubing and the casing with the tubing present are recorded. A frequency spectrum from the recorded waveforms is determined. Amplitudes of the returning acoustic energy at one or more preselected frequency(s) of interest of a range of frequencies at which the amplitudes are noticeably affected by cement bond quality for the particular casing/tubing configuration are determined. The determined amplitudes are compared with one or more baseline amplitudes to look for indications of cement bond quality. Other aspects involve time domain analysis.

Abstract: A caliper-arm-retention mechanism for a caliper tool is disclosed. The retention mechanism includes a selectively movable retention sleeve and a pivot arm that cooperate to constrain relative translational motion between the pivot arm and a caliper arm pivotally engaged with the pivot arm while at the same time allowing relative rotational movement of the caliper arm and pivot arm. The retention sleeve may be selectively repositioned using a threaded nut configured to push the sleeve toward the pivot arm or pull the sleeve away from the pivot arm, depending on the direction of rotation of the nut.

Abstract: A sensor comprising three electrodes forming two electrode pairs, each pair having a gap between the electrodes, is disclosed. An electrically insulating layer is disposed in the gap of one electrode pair. The sensor may include a RC oscillator circuit connected to the electrode pair having the insulating layer such that the electrode pair contributes to the capacitance of the circuit. The sensor may include a power supply connected to the other electrode pair to provide a voltage across and current through material in the pair's gap. The sensor may be disposed in a borehole to allow borehole fluid to enter the gaps and the RC oscillator circuit and power supply may be operated to provide a measure of capacitance and resistance characteristics of the borehole fluid.

Abstract: A foam-level detector is disclosed. The foam-level detector includes mesh disposed on one or more arms attached to a carrier. The carrier is configured to engage a tube so as to be slidable along the longitudinal axis of the tube. The mesh is configured to engage a foam layer such as to float at or near the surface of the foam. The arms may be pivotally attached to the carrier. The carrier may include a magnet configured to magnetically engage a magnet disposed in the tube. The magnet in the tube may be configured to electrically connect two materials, each material having an electrical resistance per unit length of the material. A measure of the resistance of the conductive path formed by the magnet in the tube and the two materials may be used to infer the position of the foam-float along the tube.

Abstract: A sensor comprising three electrodes forming two electrode pairs, each pair having a gap between the electrodes, is disclosed. An electrically insulating layer is disposed in the gap of one electrode pair. The sensor may include a RC oscillator circuit connected to the electrode pair having the insulating layer such that the electrode pair contributes to the capacitance of the circuit. The sensor may include a power supply connected to the other electrode pair to provide a voltage across and current through material in the pair's gap. The sensor may be disposed in a borehole to allow borehole fluid to enter the gaps and the RC oscillator circuit and power supply may be operated to provide a measure of capacitance and resistance characteristics of the borehole fluid.

Abstract: A caliper-arm-retention mechanism for a caliper tool is disclosed. The retention mechanism includes a selectively movable retention sleeve and a pivot arm that cooperate to constrain relative translational motion between the pivot arm and a caliper arm pivotally engaged with the pivot arm while at the same time allowing relative rotational movement of the caliper arm and pivot arm. The retention sleeve may be selectively repositioned using a threaded nut configured to push the sleeve toward the pivot arm or pull the sleeve away from the pivot arm, depending on the direction of rotation of the nut.

Abstract: A caliper-arm-position sensor comprising a differential variable reluctance transducer (DVRT) and circuits to drive the DVRT with a substantially sinusoidal signal and to sample a signal at the DVRT once per drive-signal cycle at a predetermined position in the drive-signal cycle is disclosed.

Abstract: Various downhole logging tools and methods of using and making the same are disclosed. In one aspect, a downhole logging tool for inspecting one or more well tubulars includes a housing adapted to be supported in the one or more well tubulars by a support cable. A first transmitter, a second transmitter and a third transmitter are positioned in longitudinally spaced-apart relation in the housing and are operable to generate magnetic fields. Driving circuitry is operatively coupled to the first transmitter, the second transmitter and the third transmitter to selectively fire the first transmitter, the second transmitter and the third transmitter in multiple transmission modes to generate magnetic fields to stimulate pulsed eddy currents in the one or more well tubulars. A first receiver is positioned in the housing to sense decaying magnetic fields created by the pulsed eddy currents.

Abstract: Various downhole logging tools and methods of using and making the same are disclosed. In one aspect, a downhole logging tool for inspecting a well casing is provided that includes a housing adapted to be supported in the well casing by a support cable. A transmitter is positioned in the housing and operable to generate a magnetic field. Plural receivers are positioned in the housing in circumferentially-spaced apart relation and are operable to sense the magnetic field with azimuthal sensitivity. Electronic circuitry is operatively coupled to the receivers to determine a parameter of the sensed magnetic field and determine a characteristic of the well casing based on the parameter.

Abstract: A constant force device has at least a first non-constant axial force driving the first set of arms and a second non-constant axial force driving the second set of arms, where the two sets of arms are offset from one another by 90°. Each of the non-constant axial forces is converted to a radially extending force by the interaction of a force guide and actuator. The force guide is attached to the inner mandrel of the constant force device and is shaped to produce an essentially constant radially extending force through the entire range of motion of the arms. Typically each arm of the pair of arms has a pivoting arm and a telescoping arm where the joint between the pivoting arm and telescoping arm has one or more wheels to reduce friction as the constant force device moves through the tubular. Generally the first pair of arms is opposed to and overlaps by some distance the second pair of arms where the second pair of arms is 90° offset from the first pair of arms.

Abstract: A method for initializing the input of each of m receiver channels of a receiving transducer in a well logging tool comprising the steps of selecting a logging tool having a multi-element receiving transducer wherein each element of the multi-element receiving transducer operates in an anti-resonant mode below its resonant frequency, and executing a routine in an initialization mode wherein a predetermined number of run cycles are operated and receiver input responses are measured and averaged for each of the m channels while transmitter firing signals are disabled.

Abstract: A method for initializing the input of each of m receiver channels of a receiving transducer in a well logging tool comprising the steps of selecting a logging tool having a multi-element receiving transducer wherein each element of the multi-element receiving transducer operates in an anti-resonant mode below its resonant frequency, and executing a routine in an initialization mode wherein a predetermined number of run cycles are operated and receiver input responses are measured and averaged for each of the m channels while transmitter firing signals are disabled.

Abstract: A method for initializing the input of each of m receiver channels of a receiving transducer in a well logging tool comprising the steps of selecting a logging tool having a multi-element receiving transducer wherein each element of the multi-element receiving transducer operates in an anti-resonant mode below its resonant frequency, and executing a routine in an initialization mode wherein a predetermined number of run cycles are operated and receiver input responses are measured and averaged for each of the m channels while transmitter firing signals are disabled.