Measurement of nonlinear properties of formation using sonic borehole tool while changing pressure in borehole

A method of measuring a nonlinear property of an earth formation traversed by a borehole having borehole fluid, by utilizing a sonic logging tool having at least one of a monopole and a dipole source, and at least one sonic detector, said method comprising:

• a) at a location in the borehole which is at a first pressure, using the sonic logging tool to generate and measure a first frequency dependent velocity of a flexural wave (v.sub.ref.sup.flexural);
• b) pressurizing the borehole at said location in the borehole to a second pressure different than said first pressure;
• c) using the sonic logging tool to generate and measure a second frequency dependent velocity of a flexural wave (v.sup.flexural);
• d) determining an indication of a nonlinear parameter of the earth formation by determining a fractional change (v.sup.flexural -v.sub.ref.sup.flexural) /v.sub.ref.sup.flexural in said flexural wave velocities, and subtracting from said fractional change in said flexural wave velocities a component related to the borehole fluid and a component related to linear aspects of the formation to provide a nonlinear formation component.

Apparatus for measuring a nonlinear property of an earth formation traversed by a borehole having borehole fluid therein, comprising:

• a) a sonic borehole tool with a sonic source which generates a first Stoneley wave in the borehole with said borehole at a first pressure, and a sonic detector, wherein said sonic borehole measures an indication of a first frequency dependent velocity of said first Stoneley wave (v.sub.ref.sup.Stoneley) to provide first measurements;
• b) borehole pressurizing means for pressurizing the borehole at a location of said sonic borehole tool in the borehole to a second pressure different than said first pressure, wherein said sonic source of said sonic borehole logging tool generates a second Stoneley wave, and said sonic borehole tool measures indications of a second frequency dependent velocity of said second Stoneley wave (v.sup.Stoneley) with said borehole pressurized at said second pressure to provide second measurements;
• d) processing means for obtaining said first measurements and said second measurements and for determining therefrom an indication of a nonlinear parameter of the earth formation by determining a fractional change (v.sup.Stoneley -v.sub.ref.sup.Stoneley)/v.sub.ref.sup.Stoneley in said Stoneley wave velocities, and subtracting from said fractional change in said Stoneley wave velocities a component related to the borehole fluid and a component related to linear aspects of the formation to provide a nonlinear formation component.

Apparatus for measuring a nonlinear property of an earth formation traversed by a borehole having borehole fluid therein, comprising:

• a) a sonic borehole tool with a sonic source which generates a first flexural wave in the borehole with said borehole at a first pressure, and a sonic detector, wherein said sonic borehole measures an indication of a first frequency dependent velocity of said first flexural wave (v.sub.ref.sup.flexural) to provide first measurements;
• b) borehole pressurizing means for pressurizing the borehole at a location of said sonic borehole tool in the borehole to a second pressure different than said first pressure, wherein said sonic source of said sonic borehole logging tool generates a second flexural wave, and said sonic borehole tool measures indications of a second frequency dependent velocity of said second flexural wave (v.sup.flexural) with said borehole pressurized at said second pressure to provide second measurements;
• d) processing means for obtaining said first measurements and said second measurements and for determining therefrom an indication of a nonlinear parameter of the earth formation by determining a fractional change (v.sup.flexural -v.sub.ref.sup.flexural)/v.sub.ref.sup.flexural in said flexural wave velocities, and subtracting from said fractional change in said flexural wave velocities a component related to the borehole fluid and a component related to linear aspects of the formation to provide a nonlinear formation component.

A method of characterizing an underground formation surrounding a borehole, comprising:

• a) pressurizing the borehole at a location at a first pressure;
• b) generating a first sonic signal at the location at the first pressure;
• c) measuring a first frequency dependent Stoneley wave velocity at the location at the first pressure;
• d) pressurizing the borehole at the location to a second pressure different to the first pressure;
• e) generating a second sonic signal at the location at the second pressure;
• f) measuring a second frequency dependent Stoneley wave velocity at the location at the second pressure;
• g) determining a frequency dependent acoustoelastic coefficient from the first and second frequency dependent velocities;
• h) obtaining an indication of a nonlinear property of the formation from the frequency dependent acoustoelastic coefficient;
• and
• i) using the indication of the nonlinear property to characterize the formation.

A method of characterizing an underground formation surrounding a borehole, comprising:

• a) pressurizing the borehole at a location at a first pressure;
• b) generating a first sonic signal at the location at the first pressure;
• c) measuring a first frequency dependent flexural wave velocity at the location at the first pressure;
• d) pressurizing the borehole at the location to a second pressure different to the first pressure;
• e) generating a second sonic signal at the location at the second pressure;
• f) measuring a second frequency dependent flexural wave velocity at the location at the second pressure;
• g) determining a frequency dependent acoustoelastic coefficient from the first and second frequency dependent velocities;
• h) obtaining an indication of a nonlinear property of the formation from the frequency dependent acoustoelastic coefficient;
• and
• i) using the indication of the nonlinear property to characterize the formation.

Apparatus for characterizing an underground formation surrounding a borehole, comprising:

• a) a sonic borehole tool positionable at a location in the borehole;
• b) means for pressurizing the borehole at the location to a first pressure and a second pressure which is different from the first pressure;
• c) a monopole sonic signal source in the tool for generating first and second sonic signals at the first and second pressures respectively;
• d) a detector in the tool for measuring first and second frequency dependent Stoneley wave velocities at the first and second pressures respectively;
• e) means for determining a frequency dependent acoustoelastic coefficient from the first and second frequency dependent velocities;
• and
• f) means for obtaining an indication of a nonlinear property of the formation from the frequency dependent acoustoelastic coefficient so as to characterize the formation.

Apparatus for characterizing an underground formation surrounding a borehole, comprising:

• a) a sonic borehole tool positionable at a location in the borehole;
• b) means for pressurizing the borehole at the location to a first pressure and to a second pressure which is different from the first pressure;
• c) a dipole sonic signal source in the tool for generating first and second sonic signals at the first and second pressures respectively;
• d) a detector in the tool for measuring first and second frequency dependent flexural wave velocities at the first and second pressures respectively;
• e) means for determining a frequency dependent acoustoelastic coefficient from the first and second frequency dependent velocities;
• and
• f) means for obtaining an indication of a nonlinear property of the formation from the frequency dependent acoustoelastic coefficient so as to characterize the formation.