Apparatus and method using measurements taken while drilling to map mechanical boundaries and mechanical rock properties along a borehole
The present disclosure involves a novel way of using drilling vibrations generated by the deformation of a rock formation in response to forces acting on the rock formation, where the forces are related to a drill bit and/or drilling fluid system, to identify the nature and occurrence of fractures, fracture swarms and other mechanical discontinuities (boundaries) such as bedding planes and/or faults that offset or otherwise separate rock formations with different mechanical rock properties.
1. A method of characterizing rock properties while drilling comprising:
receiving acoustical signals obtained from one or more sensors positioned on a component of a bottom hole assembly, the acoustical signals generated from a drill bit interacting with a rock formation while drilling a wellbore;
processing the acoustical signals to obtain forces acting on the drill bit interacting with the rock formation while drilling the wellbore and to obtain displacements of the drill bit interacting with the rock formation while drilling the wellbore; and
processing the forces and the displacements to obtain at least one set of data values representative of a mechanical rock property of the rock formation along the wellbore created by the drill bit interacting with the rock formation for a period of time,
wherein the acoustical signals include an axial acceleration of the drill bit and a lateral or rotary acceleration of the drill bit.
2. The method of claim 1 , the method further comprising:
identifying a change in the at least one set of data values, the change representative of the drill bit crossing a mechanical rock property discontinuity while drilling the wellbore.
3. The method of claim 1 wherein the one or more sensors are in operable communication with at least one data memory to store the acoustical signals.
4. The method of claim 1 wherein the acoustical signals are from vibrations generated from the drill bit interacting with the rock formation while drilling the wellbore.
5. The method of claim 1 wherein the acoustical signals include elastic waves.
6. The method of claim 1 wherein processing the acoustical signals comprises obtaining the root mean square of the axial acceleration of the drill bit and the root mean square of the lateral or rotary acceleration of the drill bit.
7. The method of claim 6 wherein processing the acoustical signals further comprises obtaining an axial displacement of the drill bit and a lateral or rotary displacement of the drill bit.
8. The method of claim 7 wherein processing the acoustical signals to obtain the at least one set of data values comprises processing the acoustical signals to obtain at least one of Poisson's ratio and Young's Modulus of Elasticity.
9. The method of claim 8 further comprising identifying a change in the at least one set of data values, the change representative of the drill bit crossing a mechanical rock property discontinuity while drilling the wellbore, and wherein the at least one set of data values comprises a first set of data values for Poisson's ratio computed based on a vertical transverse isotropic media along the wellbore, and a second set of data values for Poisson's ratio computed based on a horizontal transverse isotropic media along the wellbore, the change representative of the drill bit crossing a mechanical rock property discontinuity relates to a change between the first set of data values for Poisson's ratio and the second set of data values for Poisson's ratio.
10. The method of claim 9 where Poisson's ratio is ν and Young's modulus of Elasticity is E, and where the first set of data values and the second set of data values are computed according to:
σ
3
σ
1
=
E
3
ɛ
3
σ
1
+
2
υ
31
Where, the first set of data values are computed with:
σ1=RMS of lateral or rotary acceleration of the drill bit
σ3=RMS of axial acceleration of the drill bit
ε3=Axial displacement spectra ZFL
Where, the second set of data values are computed with:
σ3=RMS of rotary or lateral acceleration of the drill bit
σ1=RMS of axial acceleration of the drill bit
ε3=Rotary displacement spectra ZFL.
11. The method of claim 8 further comprising identifying a change in the at least one set of data values, the change representative of the drill bit crossing a mechanical rock property discontinuity while drilling the wellbore, and wherein the at least one set of data values comprises a first set of data values for Young's modulus of elasticity computed based on vertical transverse isotropic media along the wellbore, and a second set of data values for Young's modulus of elasticity computed based on horizontal transverse isotropic media along the wellbore, the change representative of the drill bit crossing a mechanical rock property discontinuity relates to a change between the first set of data values for Young's modulus of elasticity and the second set of data values for Young's modulus of elasticity.
12. The method of claim 11 where Poisson's ratio is ν and Young's modulus of Elasticity is E, and where the first set of data values and the second set of data values are computed according to:
σ
3
σ
1
=
E
3
ɛ
3
σ
1
+
2
υ
31
Where, the first set of data values are computed with:
σ1=RMS of lateral or rotary acceleration of the drill bit
σ3=RMS of axial acceleration of the drill bit
ε3=Axial displacement spectra ZFL
Where, the second set of data values are computed with:
σ1=RMS of rotary or lateral acceleration of the drill bit
σ1=RMS of axial acceleration of the drill bit
ε3=Rotary displacement spectra ZFL.
13. The method of claim 1 further comprising:
generating a well log spatially identifying mechanical rock property discontinuities along the wellbore using the mechanical rock properties, the mechanical rock property discontinuities indicative of preexisting fractures.
14. The method of claim 1 further comprising:
receiving dynamic drilling data related to the bottom hole assembly, the dynamic drilling data associated with the drill bit interacting with the rock formation while drilling; and
processing the acoustical signals and the dynamic drilling data to obtain at least one set of data values representative of a mechanical rock property of the rock formation along a wellbore created by the drill bit interacting with the rock formation for a period of time.
15. A method of characterizing rock properties while drilling comprising:
receiving acoustical signals obtained from one or more sensors positioned on a component of a bottom hole assembly, the acoustical signals generated from a drill bit interacting with a rock formation while drilling a wellbore;
processing the acoustical signals to obtain forces acting on the drill bit interacting with the rock formation while drilling the wellbore and to obtain displacements of the drill bit interacting with the rock formation while drilling the wellbore;
processing the forces and the displacements to obtain at least one set of data values representative of a mechanical rock property of the rock formation along the wellbore created by the drill bit interacting with the rock formation for a period of time; and
using a stress strain relationship for processing the forces and displacements to obtain the at least one set of data values representative of a mechanical rock property of the rock formation along the wellbore created by the drill bit interacting with the rock formation for a period of time.
16. A method of characterizing rock properties while drilling comprising:
receiving acoustical signals obtained from one or more sensors positioned on a component of a bottom hole assembly, the acoustical signals generated from a drill bit interacting with a rock formation while drilling a wellbore;
processing the acoustical signals to obtain forces acting on the drill bit interacting with the rock formation while drilling the wellbore and to obtain displacements of the drill bit interacting with the rock formation while drilling the wellbore; and
processing the forces and the displacements to obtain at least one set of data values representative of a mechanical rock property of the rock formation along the wellbore created by the drill bit interacting with the rock formation for a period of time,
wherein the at least one set of data values includes stiffness coefficients (Cijs).
17. The method of claim 16 wherein the stiffness coefficients (Cijs) are for transverse isotropic media.
18. The method of claim 16 wherein the stiffness coefficients comprise C 11 , C 12 , C 13 and C 33 .
19. A method of hydraulic fracturing comprising:
receiving a well log spatially identifying a plurality of mechanical discontinuities in a wellbore, the plurality of mechanical discontinuities indicative of a respective plurality of preexisting fractures along the wellbore, the well log generated from a data set representative of a mechanical rock property of a formation along the wellbore and from a bottom hole assembly, the data set generated by:
obtaining acoustical signals obtained from one or more sensors positioned on a component of the bottom hole assembly, the acoustical signals generated from a drill bit interacting with a rock formation while drilling the wellbore;
processing the acoustical signals to obtain forces acting on the drill bit interacting with the rock formation while drilling the wellbore and to obtain displacements of the drill bit interacting with the rock formation while drilling the wellbore; and
processing the forces and the displacements to obtain data set representative of a mechanical rock property of the rock formation along the wellbore created by the drill bit interacting with the rock formation; and
completing the wellbore based on the plurality of mechanical discontinuities indicative of the respective plurality of preexisting fractures,
wherein the data set includes stiffness coefficients (Cijs).
20. The method of claim 19 wherein completing comprises hydraulic fracturing the wellbore in the area of the plurality of mechanical discontinuities.
21. The method of claim 19 wherein the data set includes dynamic drilling data.
22. The method of claim 19 , further comprising:
using a stress strain relationship for processing the forces and displacements to obtain the data representative of a mechanical rock property of the rock formation along the wellbore created by the drill bit interacting with the rock formation for a period of time.
23. The method of claim 19 , the method further comprising:
identifying a change in the data set, the change representative of the drill bit crossing a mechanical rock property discontinuity while drilling the wellbore.
24. The method of claim 19 wherein the stiffness coefficients (Cijs) are for transverse isotropic media.
25. The method of claim 19 wherein the stiffness coefficients comprise C 11 , C 12 , C 13 and C 33 .
26. An apparatus comprising:
a processing unit in communication with at least one tangible machine readable media including computer executable instructions to perform the operations of:
obtaining acoustical signals obtained from one or more sensors positioned on a component of a bottom hole assembly, the acoustical signals generated from a drill bit interacting with a rock formation while drilling a wellbore;
processing the acoustical signals to obtain forces acting on the drill bit interacting with the rock formation while drilling the wellbore and to obtain displacements of the drill bit interacting with the rock formation while drilling the wellbore; and
processing the forces and the displacements to obtain at least one set of data values representative of a mechanical rock property of the rock formation along the wellbore created by the drill bit interacting with the rock formation for a period of time,
wherein the at least one set of data values includes stiffness coefficients (Cijs).
27. The apparatus of claim 26 , wherein the stiffness coefficients comprise C 11 , C 12 , C 13 and C 33 .