Method and apparatus for downhole measurements of velocity anisotropy on sidewall cores

Abstract

A method for estimating, downhole, elastic properties of a subsurface material having a bedding plane includes extracting a core sample from the subsurface material into a downhole tool, the downhole tool comprising a measurement device having a first source and a first receiver opposing the first source, the first receiver configured to receive a signal from the first source, performing at least five acoustic wave velocity measurements on the core sample in situ within the downhole tool, the measurements including compressional acoustic wave velocities and shear wave acoustic velocities with certain directions of shear acoustic wave polarization using the measurement device, estimating, with a controller, elastic properties of the core sample using the at least five acoustic wave velocity measurements, and providing an output signal comprising the elastic properties to an output signal receiving device.

What is claimed is: 
     
         1 . A method for estimating, downhole, elastic properties of a subsurface material having a bedding plane, the method comprising:
 extracting a core sample from the subsurface material into a downhole tool, the downhole tool comprising a measurement device having a first source and a first receiver opposing the first source, the first receiver configured to receive a signal from the first source;   performing at least five acoustic wave velocity measurements on the core sample in situ within the downhole tool, the measurements including compressional acoustic wave velocities and shear wave acoustic velocities with certain directions of shear acoustic wave polarization using the measurement device;   estimating, with a controller, elastic properties of the core sample using the at least five acoustic wave velocity measurements; and   providing an output signal comprising the elastic properties to an output signal receiving device.   
     
     
         2 . The method according to  claim 1 , further comprising conveying the downhole tool through a borehole penetrating the subsurface material. 
     
     
         3 . The method according to  claim 1 , wherein performing the at least five acoustic wave velocity measurements comprises:
 performing a first measurement with the first source and first receiver in a first position;   rotating the measurement device relative to the core sample by 45° such that the first source and the first receiver are in a second position;   performing a second measurement with the first source and the first receiver in the second position;   rotating the measurement device relative to the core sample by 45° such that the first receiver and the second receiver are in a third position, wherein the third position is not equal to the first position; and   performing a third measurement with the first source and the first receiver in the third position.   
     
     
         4 . The method according to  claim 1 , wherein the measurement device comprises a second source and a second receiver opposing the second source, the second receiver configured to receive a signal from the second source. 
     
     
         5 . The method according to  claim 4 , wherein performing the at least five acoustic wave velocity measurements comprises:
 performing a first measurement with the first source and first receiver at a first position and the second source and second receiver at a second position;   rotating the measurement device relative to the core sample by 45° such that the first source and the first receiver are in the second position and the second source and second receiver are in a third position; and   performing a second measurement with at least the second source and the second receiver in the third position.   
     
     
         6 . The method according to  claim 1 , wherein the measurement device comprises:
 a second source and a second receiver opposing the second source, the second receiver configured to receive a signal from the second source, wherein a line passing through the second source and second receiver is 45° offset from a line passing through the first source and first receiver; and   a third source and a third receiver opposing the third source, the third receiver configured to receive a signal from the third source, wherein a line passing through the third source and third receiver is 45° offset from a line passing through the second source and second receiver and 90° offset from the line passing through the first source and first receiver.   
     
     
         7 . The method according to  claim 1 , further comprising:
 conveying the extracted core sample to the surface of the earth; and   performing a correction operation such that at least five acoustic wave velocity measurements are oriented to the bedding plane of the core sample.   
     
     
         8 . The method according to  claim 1 , wherein the at least five acoustic wave velocity measurements comprise:
 a parallel compression wave velocity measurement (V PH ) of a compression acoustic wave traveling parallel to the bedding plane;   a parallel shear wave velocity measurement (V SH ) of a shear acoustic wave traveling parallel to the bedding plane and polarized parallel to the bedding plane;   a perpendicular compression wave velocity (V PV ) of a compression acoustic wave traveling perpendicular to the bedding plane;   a perpendicular shear wave velocity measurement (V SV1 ) of a shear acoustic wave traveling perpendicular to the bedding plane and polarized parallel to the bedding plane; and   a quasi-compression wave velocity (V qP ) of a compression acoustic wave traveling at a 45° angle with respect to a direction of the bedding plane.   
     
     
         9 . The method according to  claim 1 , wherein providing an output signal comprises using an output interface. 
     
     
         10 . The method according to  claim 1 , further comprising at least one of displaying on a display the estimated elastic properties, recording the estimated elastic properties on a non-transitory computer readable medium, and printing the estimated elastic properties using a printer. 
     
     
         11 . An apparatus for estimating, downhole, elastic properties of a subsurface material having a bedding plane, the apparatus comprising:
 a downhole device configured to extract a core sample from the subsurface material into the downhole tool;   a measurement device disposed in the downhole tool having a first source and a first receiver opposing the first source, the first receiver configured to receive a signal from the first source, the measurement device configured to perform at least five acoustic wave velocity measurements on the core sample in situ within the downhole tool, the measurements including compressional acoustic wave velocities and shear wave acoustic velocities with certain directions of shear acoustic wave polarization using the measurement device; and   a controller in communication with the measurement device and configured to estimate elastic properties of the core sample using the at least five acoustic wave velocity measurements.   
     
     
         12 . The apparatus according to  claim 11 , further comprising a carrier configured to convey the downhole tool through a borehole penetrating the subsurface material. 
     
     
         13 . The apparatus according to  claim 11 , wherein the measurement device is configured to:
 perform a first measurement with the first source and first receiver in a first position;   rotate relative to the core sample by 45° such that the first source and the first receiver are in a second position;   perform a second measurement with the first source and the first receiver in the second position;   rotate relative to the core sample by 45° such that the first receiver and the second receiver are in a third position, wherein the third position is not equal to the first position; and   perform a third measurement with the first source and the first receiver in the third position.   
     
     
         14 . The apparatus according to  claim 11 , wherein the measurement device comprises a second source and a second receiver opposing the second source, the second receiver configured to receive a signal from the second source. 
     
     
         15 . The apparatus according to  claim 14 , wherein the measurement device is configured to:
 perform a first measurement with the first source and first receiver at a first position and the second source and second receiver at a second position;   rotate relative to the core sample by 45° such that the first source and the first receiver are in the second position and the second source and second receiver are in a third position; and   perform a second measurement with at least the second source and the second receiver in the third position.   
     
     
         16 . The apparatus according to  claim 11 , wherein the measurement device comprises:
 a second source and a second receiver opposing the second source, the second receiver configured to receive a signal from the second source, wherein a line passing through the second source and second receiver is 45° offset from a line passing through the first source and first receiver; and   a third source and a third receiver opposing the third source, the third receiver configured to receive a signal from the third source, wherein a line passing through the third source and third receiver is 45° offset from a line passing through the second source and second receiver and 90° offset from the line passing through the first source and first receiver.   
     
     
         17 . The apparatus according to  claim 11 , wherein the controller is configured to perform a correction operation such that at least five acoustic wave velocity measurements are oriented to the bedding plane of the core sample. 
     
     
         18 . The apparatus according to  claim 11 , wherein the at least five acoustic wave velocity measurements comprise:
 a parallel compression wave velocity measurement (V PH ) of a compression acoustic wave traveling parallel to the bedding plane;   a parallel shear wave velocity measurement (V SH ) of a shear acoustic wave traveling parallel to the bedding plane and polarized parallel to the bedding plane;   a perpendicular compression wave velocity (V PV ) of a compression acoustic wave traveling perpendicular to the bedding plane;   a perpendicular shear wave velocity measurement (V SV1 ) of a shear acoustic wave traveling perpendicular to the bedding plane and polarized parallel to the bedding plane; and   a quasi-compression wave velocity (V qP ) of a compression acoustic wave traveling at a 45° angle with respect to a direction of the bedding plane.   
     
     
         19 . The apparatus according to  claim 11 , further comprising an output interface configured to output the estimation of the controller. 
     
     
         20 . The apparatus according to  claim 11 , further comprising at least one of a display to display the estimated elastic properties, a recorder to record the estimated elastic properties on a non-transitory computer readable medium, or a printer for printing the estimated elastic properties.