Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Well logging
Patent
1995-10-04
1997-01-28
Lobo, Ian J.
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Well logging
367 25, 367 75, G01V 140
Patent
active
055983774
ABSTRACT:
A method of correcting compressional velocity well log measurements for the effects of gas in the pore space of earth formations. The method includes the steps of determining a relationship between measurements of shear velocity and a ratio of measurements of compressional velocity with respect to shear velocity for the earth formations for when the earth formations are substantially liquid-filled. A first boundary of the relationship is determined for when the earth formations are substantially composed of shale, a second boundary is determined for when the earth formations are substantially devoid of shale. A cutoff is determined by adjusting an ordinate intercept value of the relationship to substantially include shear velocity and compressional velocity measurements corresponding to the earth formation having gas in the pore space. The cutoff is set to substantially exclude shear and compressional velocity measurements corresponding to the earth formations being substantially liquid-filled. For each measurement of shear and compressional velocity included within the cutoff a shale volume and a corrected ratio of compressional velocity to shear velocity is determined. The corrected ratio is determined by scaling with respect to the shale volume between the first boundary the said second boundary. For each corrected ratio thus determined, the corrected ratio is applied to a corresponding measurement of shear velocity to calculate corrected compressional velocity.
REFERENCES:
patent: 4636994 (1987-01-01), Fertl et al.
patent: 4692910 (1987-09-01), Sondergeld et al.
patent: 4972384 (1990-11-01), Williams
Fishburn Todd K.
Thomas Smith Jane E.
Fagin Richard A.
Lobo Ian J.
Western Atlas International Inc.
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