Sonic well logging for alteration detection
First Claim
1. A method for determining alteration of a region of an earth formation surrounding an earth borehole, comprising the steps of:
- providing a logging device that is moveable through the borehole;
transmitting sonic energy into the formation and receiving, at a plurality of transmitter-to-receiver spacings on said logging device, sonic energy that has traveled through the formation, and producing signals representative of the received sonic energy for said plurality of transmitter-to-receiver spacings;
determining, from said signals, sonic transit times and differential transit times for the respective transmitter-to-receiver spacings;
deriving a test statistic from said differential transit times; and
determining the presence of alteration of a region of the formations from said test statistic.
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Accused Products
Abstract
A method for determining alteration of a region of an earth formation surrounding an earth borehole, comprising the steps of providing a logging device that is moveable through the borehole; transmitting sonic energy into the formation and receiving, at a plurality of transmitter-to-receiver spacings, sonic energy that has traveled through the formation, and producing signals representative of the received sonic energy for the plurality of transmitter-to-receiver spacings; determining sonic transit times and differential transit times for the respective transmitter-to-receiver spacings; deriving a test statistic from the differential transit times; and determining the presence of alteration of a region of the formations from the test statistic. An associated apparatus for carrying out the method is also described.
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Citations
35 Claims
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1. A method for determining alteration of a region of an earth formation surrounding an earth borehole, comprising the steps of:
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providing a logging device that is moveable through the borehole;
transmitting sonic energy into the formation and receiving, at a plurality of transmitter-to-receiver spacings on said logging device, sonic energy that has traveled through the formation, and producing signals representative of the received sonic energy for said plurality of transmitter-to-receiver spacings;
determining, from said signals, sonic transit times and differential transit times for the respective transmitter-to-receiver spacings;
deriving a test statistic from said differential transit times; and
determining the presence of alteration of a region of the formations from said test statistic. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
where DTTi are the individual differential transit times, DTT is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, and m and c are constants.
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12. The method as defined by claim 2, wherein said test statistic T1 is of the form
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i ( DTT i - DTT _ ) 2 min m < 0 , c ∑ i ( DTT i - mTR i - c ) 2 where DTTi are the individual differential transit times, {overscore (DTT)} is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, and m and c are constants.
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13. The method as defined by claim 2, wherein said test statistic T1 is of the form
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i W ii ( DTT i - DTT _ ) 2 min m < 0 , c ∑ i W ii ( DTT i - mTR i - c ) 2 where DTTi are the individual differential transit times, {overscore (DTT)} is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, m and c are constants, and Wii are weighing coefficients on the diagonal of the inverse of the covariance matrix.
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14. The method as defined by claim 2, wherein said test statistic T1 is of the form
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i ( DTT i - DTT _ ) 2 min R c , c 1 , m < 0 , c 0 < mR c + c 1 ∑ i ( DTT i - p R c , m , c 0 , c 1 ( TR i ) ) 2 where where DTTi are the individual differential transit times, {overscore (DTT)} is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, and m, c0, c1, and Rc are constants.
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15. Apparatus for determining alteration of a region of an earth formation surrounding an earth borehole, comprising:
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a logging device that is moveable through the borehole;
means on said logging device for transmitting sonic energy into the formation and receiving, at a plurality of transmitter-to-receiver spacings on said logging device, sonic energy that has traveled through the formation, and for producing signals representative of the received sonic energy for said plurality of transmitter-to-receiver spacings;
means for determining, from said signals, sonic transit times and differential transit times for the respective transmitter-to-receiver spacings;
means for deriving a test statistic from said differential transit times; and
means for determining the presence of alteration of a region of the formations from said test statistic. - View Dependent Claims (16)
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17. A method for determining alteration of a region of the earth formation, for use in conjunction with a technique for sonic logging of an earth formation that includes:
- providing a logging device that is moveable through the borehole;
transmitting sonic energy into the formation and receiving, at a plurality of transmitter-to-receiver spacings, sonic energy that has traveled through the formation, and producing signals representative of the received sonic energy for said plurality of transmitter-to-receiver spacings;
comprising the steps of;determining, from said signals, sonic transit times and differential transit times for the respective transmitter-to-receiver spacings;
deriving a test statistic from said differential transit times; and
determining the presence of alteration of a region of the formations from said test statistic. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26)
where DTTi are the individual differential transit times, {overscore (DTT)} is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, and m and c are constants.
- providing a logging device that is moveable through the borehole;
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25. The method as defined by claim 17, wherein said test statistic T1 is of the form
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i W ii ( DTT i - DTT _ ) 2 min m < 0 , c ∑ i W ii ( DTT i - mTR i - c ) 2 where DTTi are the individual differential transit times, {overscore (DTT)} is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, m and c are constants, and Wii are weighing coefficients on the diagonal of the inverse of the covariance matrix.
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26. The method as defined by claim 17, wherein said test statistic T1 is of the form
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i ( DTT i - DTT _ ) 2 min R c , c 1 , m < 0 , c 0 < mR c + c 1 ∑ i ( DTT i - p R c , m , c 0 , c 1 ( TR i ) ) 2 where where DTTi are the individual differential transit times, DTT is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, and m, c0, c1, and Rc are constants.
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27. A method for determining whether a region of an earth formation surrounding an earth borehole is homogeneous, comprising the steps of:
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providing a logging device that is moveable through the borehole;
transmitting sonic energy into the formation and receiving, at a plurality of transmitter-to-receiver spacings on said logging device, sonic energy that has traveled through the formation, and producing signals representative of the received sonic energy for said plurality of transmitter-to-receiver spacings;
determining, from said signals, sonic transit times and differential transit times for the respective transmitter-to-receiver spacings;
deriving a test statistic from said differential transit times; and
determining, from said test statistic, whether said region of the formation is homogeneous. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35)
where DTTi are the individual differential transit times, {overscore (DTT)} is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, and m and c are constants.
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34. The method as defined by claim 27, wherein said test statistic T1 is of the form
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i W ii ( DTT i - DTT _ ) 2 min m < 0 , c ∑ i W ii ( DTT i - mTR i - c ) 2 where DTTi are the individual differential transit times, {overscore (DTT)} is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, m and c are constants, and Wii are weighing coefficients on the diagonal of the inverse of the covariance matrix.
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35. The method as defined by claim 27, wherein said test statistic T1 is of the form
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i ( DTT i - DTT _ ) 2 min R c , c 1 , m < 0 , c 0 < mR c + c 1 ∑ i ( DTT i - p R c , m , c 0 , c 1 ( TR i ) ) 2 where where DTTi are the individual differential transit times, {overscore (DTT)} is the average of the differential transit times, TRi are the individual transmitter-to-receiver spacings, and m, c0, c1, and Rc are constants.
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Specification