Acoustic imaging while cutting
A method and apparatus for radially cutting tubulars in a downhole environment by emitting acoustic energy into the jet, the acoustic energy having a wavelength selected such that the jet acts as a waveguide, detecting reflected acoustic energy in the jet, and determining the depth of cut from a travel time of the acoustic energy.
1. A method for determining depth of cut in a pipe wall of an abrasive fluid jet, comprising:
emitting acoustic energy into the jet, the acoustic energy having a wavelength selected such that the jet acts as a waveguide;
detecting reflected acoustic energy in the jet; and
analyzing the detected acoustic energy to determine when the cut is completed.
2. The method of claim 1 further comprising determining when the pipe wall is fully severed when one of the following occurs: (i) the detected energy indicates a step change in reflected acoustic energy travel time or (ii) there is a substantial absence of detected reflected acoustic energy.
3. The method claim 1 , wherein the step of determining the depth of cut from a travel time of acoustic energy further comprises forming an amplitude/travel time history of detected reflected acoustic energy.
4. The method of claim 3 , wherein the step of determining the depth of cut from a travel time of acoustic energy further comprises analyzing the amplitude/travel time history using a Hilbert Transform.
5. A method for severing a pipe wall of a first tubular section comprising:
discharging an abrasive fluid jet from a jet nozzle such that the abrasive fluid jet cuts into the first tubular section;
emitting acoustic energy into the abrasive fluid jet, the acoustic energy having a wavelength selected such that the abrasive fluid jet acts as a waveguide;
detecting reflected acoustic energy in the abrasive fluid jet; and
analyzing the detected reflected acoustic energy to determine when a cut in the pipe wall is completed.
6. The method of claim 5 further comprising using the abrasive fluid jet to sever a second tubular section wherein the first tubular section is nested inside the second tubular section.
7. The method of claim 5 , wherein the step of emitting acoustic energy into the abrasive fluid jet is pulsed such that the acoustic energy emitted is intermittent.
8. The method of claim 7 further comprising comparing the reflected acoustic energy in the abrasive fluid jet to a background acoustic energy.