Use of an effective tool model in sonic logging data processing
First Claim
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1. A method of estimating a shear modulus in an anisotropic formation surrounding a borehole, comprising:
- measuring Stoneley dispersion around a vertical borehole with an acoustic tool;
calculating a horizontal shear modulus c66 from the measured Stoneley dispersion;
accounting for acoustic tool bias on the horizontal shear modulus c66 calculation by replacing the acoustic tool structure with a resonance-impedance model that comprises an equivalent surface impedance placed concentrically with a substantially vertical X3- axis and simplifying the equivalent surface impedance to a column having frequency-dependent complex material properties and a surface impedance condition at an interface between the acoustic tool and a borehole fluid;
introducing the equivalent surface impedance to an open hole and calculating fundamental eigenmodes associated with a lowest-order axi-symmetric Stoneley mode of the equivalent surface impedance using a mode-search routine;
accounting for near-borehole alteration effects on horizontal shear slowness estimation; and
storing an indication of the shear modulus.
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Abstract
Methods and apparatus facilitating radial profiling of shear slowness are disclosed. According to some aspects of the invention, acoustic tool bias is accounted for in the calculation of radial profiles. According so some aspects, acoustic tool bias is accounted for by replacing acoustic tool structure with a resonance-impedance model. The resonance-impedance modeling according to principles of the present invention is applicable to vertical, deviated, and horizontal boreholes.
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6 Claims
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1. A method of estimating a shear modulus in an anisotropic formation surrounding a borehole, comprising:
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measuring Stoneley dispersion around a vertical borehole with an acoustic tool; calculating a horizontal shear modulus c66 from the measured Stoneley dispersion; accounting for acoustic tool bias on the horizontal shear modulus c66 calculation by replacing the acoustic tool structure with a resonance-impedance model that comprises an equivalent surface impedance placed concentrically with a substantially vertical X3- axis and simplifying the equivalent surface impedance to a column having frequency-dependent complex material properties and a surface impedance condition at an interface between the acoustic tool and a borehole fluid; introducing the equivalent surface impedance to an open hole and calculating fundamental eigenmodes associated with a lowest-order axi-symmetric Stoneley mode of the equivalent surface impedance using a mode-search routine; accounting for near-borehole alteration effects on horizontal shear slowness estimation; and storing an indication of the shear modulus. - View Dependent Claims (2, 3, 4, 5, 6)
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