Jane E Thomas

US Patent:

55983774, Jan 28, 1997

Filed:

Oct 4, 1995

Appl. No.:

8/539123

Inventors:

Todd K. Fishburn - Houston TX
Jane E. Thomas Smith - Houston TX

Assignee:

Western Atlas International, Inc. - Houston TX

International Classification:

G01V 140

US Classification:

367 31

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.