A distributed acoustic system (DAS) may comprise an interrogator and an umbilical line attached at one end to the interrogator, a downhole fiber attached to the umbilical line at the end opposite the interrogator. The interrogator may further include a proximal circulator, a distal circulator connected to the proximal circulator by a first fiber optic cable, and a second fiber optic cable connecting the proximal circulator and the distal circulator.

A method and apparatus for determining a pressure in an annulus between an inner casing and an outer casing. An acoustic transducer is disposed within the casing at a selected depth within the inner casing and is configured to generate an acoustic pulse and receive a reflection of the acoustic pulse from the inner casing. A time of flight is measured of the acoustic pulse to the inner surface of the inner casing. An inner diameter of the inner casing is determined from the time of flight. The pressure in the annulus is determined from the inner diameter. A processor can be used to measure time and determine inner diameter and annulus pressure.

A method and apparatus for determining a pressure in an annulus between an inner casing and an outer casing. An acoustic transducer is disposed within the casing at a selected depth within the inner casing and is configured to generate an acoustic pulse and receive a reflection of the acoustic pulse from the inner casing. A time of flight is measured of the acoustic pulse to the inner surface of the inner casing. An inner diameter of the inner casing is determined from the time of flight. The pressure in the annulus is determined from the inner diameter. A processor can be used to measure time and determine inner diameter and annulus pressure.

A downhole tool having an acoustic transducer for downhole measurements. A backing is in contact with an inner surface of the transducer. A first structure is coupled to a first housing. A second structure is coupled to a second housing. A member includes first, second, and third portions. The first portion is coupled to the first structure. The second portion is coupled to the second structure. At least one of the first and second structures is coupled to the member and has a degree of freedom relative to the member. The third portion extends longitudinally through the backing between the first and second portions such that compressional forces on the first and second housings are transferred through the first and second structures and the backing. A canister contacts an outer surface of the transducer and exerts radial forces on the transducer when exposed to pressures higher than atmospheric pressure.

A downhole tool having an acoustic transducer for downhole measurements. A backing is in contact with an inner surface of the transducer. A first structure is coupled to a first housing. A second structure is coupled to a second housing. A member includes first, second, and third portions. The first portion is coupled to the first structure. The second portion is coupled to the second structure. At least one of the first and second structures is coupled to the member and has a degree of freedom relative to the member. The third portion extends longitudinally through the backing between the first and second portions such that compressional forces on the first and second housings are transferred through the first and second structures and the backing. A canister contacts an outer surface of the transducer and exerts radial forces on the transducer when exposed to pressures higher than atmospheric pressure.

An apparatus includes a mechanical wave source; a set of mechanical wave sensors in a borehole to provide subsurface wave measurements based on formation waves from the mechanical wave source, and a processor. The apparatus also includes a machine-readable medium having program code to acquire the subsurface wave measurements, select a first set of tool wave measurements based on the subsurface wave measurements, and generate a set of filtered subsurface wave measurements by filtering the subsurface wave measurements based on the first set of tool wave measurements. The program code also includes instructions to generate a time-domain semblance map based on the set of filtered subsurface wave measurements, wherein the time-domain semblance map includes an initial set of compression wave peaks, determine a selected qualified compression wave peak based on a semblance value in the time-domain semblance map, and determine a compression wave slowness based on the selected qualified compression wave peak.

A disclosed vibration monitoring method includes: processing sensor information downhole to detect one or more vibration modes; responsively updating a vibration mode state machine; communicating a current machine state to an uphole module; deriving from said current machine state at least a primary vibration mode and associated severity; and modifying at least one drilling parameter if the severity exceeds a threshold. A disclosed drilling system implementation includes: a drill string; a rig or other deployment device that conveys the drill string into a borehole using at least one controllable drilling parameter; one or more downhole sensors providing vibration-related signals; a downhole processor that operates on the vibration-related signals to detect one or more vibration modes and responsively updates a vibration mode state machine; and an uphole module that receives the current state from the downhole processor and derives from the current state at least a primary vibration mode and severity.

A disclosed vibration monitoring method includes: processing sensor information downhole to detect one or more vibration modes; responsively updating a vibration mode state machine; communicating a current machine state to an uphole module; deriving from said current machine state at least a primary vibration mode and associated severity; and modifying at least one drilling parameter if the severity exceeds a threshold. A disclosed drilling system implementation includes: a drill string; a rig or other deployment device that conveys the drill string into a borehole using at least one controllable drilling parameter; one or more downhole sensors providing vibration-related signals; a downhole processor that operates on the vibration-related signals to detect one or more vibration modes and responsively updates a vibration mode state machine; and an uphole module that receives the current state from the downhole processor and derives from the current state at least a primary vibration mode and severity.

Some aspects relate to techniques for calibrating a logging tool. In some implementations, the logging tool may estimate certain unknown properties of a signal based on distances between transmitters and receivers of the logging tool and based on frequencies used by the transmitters and receivers. The logging tool may estimate the unknown properties by interpolating values into a mathematical function related to the above-noted distances and frequencies. After estimating the unknown properties, the logging tool may be deployed into the wellbore, where it may use the estimated properties to process signals received through a subsurface formation.

Some aspects relate to techniques for calibrating a logging tool. In some implementations, the logging tool may estimate certain unknown properties of a signal based on distances between transmitters and receivers of the logging tool and based on frequencies used by the transmitters and receivers. The logging tool may estimate the unknown properties by interpolating values into a mathematical function related to the above-noted distances and frequencies. After estimating the unknown properties, the logging tool may be deployed into the wellbore, where it may use the estimated properties to process signals received through a subsurface formation.