Sensing formation properties during wellbore construction

Patent metadata

Field	Value
Publication number	US-10774637-B2
Application number	US-201715793549-A
Country	US
Kind code	B2
Filing date	Oct 25, 2017
Priority date	Nov 4, 2016
Publication date	Sep 15, 2020
Grant date	Sep 15, 2020

Abstract

Systems and methods are disclosed that provide highly accurate and controllable measurements of rock formation properties in a wellbore. The systems and methods utilize a prescribed input signal to mechanically perturb a drill string in contact with a rock formation in order to elicit a mechanical response. Based on the input signal and the mechanical response, a transfer function is computed and analyzed, wherein the analysis uses estimates of the drill string resonances to identify rock formation resonances, which are used, in turn, to determine the rock formation properties.

First claim

The invention claimed is:

1. A method for determining properties of a formation during construction of a wellbore, the method comprising:
positioning a drill string in the wellbore so that a drill-bit of the drill string is in contact with the formation;
selecting, by a computing device, a prescribed input signal from among a plurality of different prescribed input signals, each of the plurality of different prescribed input signals being a deterministic or random signal, each of the plurality of different prescribed input signals having a varying amplitude and lasting for a fixed period, wherein the prescribed input signal acts through a motive-force source to induce a corresponding mechanical change in the drill string and wherein the prescribed input signal is selected based on one or more of the formation at an interface between the drill-bit and the formation, a particular drill string configuration, a signal to noise ratio (SNR) of the prescribed input signal, and easing/improving an estimation of mechanical harmonics of the drill string;
perturbing, for a period, one or more operating parameters of the drill-bit according to the selected prescribed input signal;
sensing, by the computing device, an output signal immediately following the period, wherein the output signal corresponds to the drill string's mechanical response to the perturbation;
converting, by the computing device, each of the selected prescribed input signal and the sensed output signal to a frequency domain;
determining, by the computing device, a transfer function based on the selected prescribed input signal and the sensed output signal, wherein the transfer function is a ratio of the sensed output signal to the selected prescribed input signal, each converted to the frequency domain, and wherein the transfer function is measured over a defined frequency range, said defined frequency range determined by the selected prescribed input signal; and
analyzing, by the computing device, the transfer function to determine the properties of the formation, wherein the analysis includes distinguishing resonances in the transfer function as being resonances from the drill string or as being resonances from the formation.

2. The method according to claim 1 , wherein the drill bit is perturbed while stationary or while drilling, and wherein the output signal represents both the drill string's mechanical response and the formation's mechanical response to the perturbing.

3. The method according to claim 1 , wherein the one or more operating parameters of the drill-bit comprise one or more of a torque, a speed, a displacement, and an axial force.

4. The method according to claim 1 , wherein the plurality of different prescribed input signals comprise a step input signal, a chirp signal, or a random white noise signal.

5. The method according to claim 4 , wherein the selection is based on a desired transfer function characteristic.

6. The method according to claim 5 , wherein the desired transfer function characteristic is a frequency, a bandwidth, or a resolution of the transfer function.

7. The method according to claim 1 , further comprising:
repeating the operations of perturbing, sensing, computing, and analyzing during the construction of the wellbore so that the determined properties of the formation are from a plurality of positions in the wellbore.

8. The method according to claim 1 , further comprising:
determining requirements for a stable wellbore or for hydraulic fracturing based on the determined properties of the formation.

9. The method according to claim 1 , further comprising:
modeling a reservoir based on the determined properties of the formation.

10. The method of claim 1 , wherein resonances from the formation and properties of the drill bit are used to create a model to determine the properties of the formation.

11. The method of claim 10 , wherein the model comprises a mass-spring-damper model.

12. A drill system for wellbore construction, comprising:
a drill string comprising a drill-bit, wherein the drill-bit contacts a formation in the wellbore;
a motive-force source coupled to the drill string, wherein the motive-force source operates the drill-hit according to operating parameters;
one or more sensors coupled to the drill string, wherein the one or more sensors detect a mechanical response of the drill string; and
a computing device comprising a processor in communication with the motive-force source and the one or more sensors, wherein the processor is configured by software instructions to:
select a prescribed input signal from among a plurality of different prescribed input signals, each of the plurality of different prescribed input signals being a deterministic or random signal, each of the plurality of different prescribed input signals having a varying amplitude and lasting for a fixed period, wherein the prescribed input signal is selected based on one or more of the formation at an interface between the drill-bit and the formation, a particular drill string configuration, a signal to noise ratio (SNR) of the prescribed input signal, and easing/improving an estimation of mechanical harmonics of the drill string;
cause the motive-force source to perturb, for a period, one or more operating parameters of the drill-bit according to the selected prescribed input signal,
receive an output signal from the one or more sensors immediately following the period, wherein the output signal corresponds to the drill string's mechanical response to the perturbation,
converting each of the selected prescribed input signal and the output signal to a frequency domain;
compute a transfer function based on the prescribed input signal and the output signal, wherein the transfer function is a ratio of the output signal to the selected prescribed input signal, each converted to the frequency domain, and wherein the transfer function is measured over a defined frequency range, said defined frequency range determined by the selected prescribed input signal; and
analyze the transfer function to determine properties of the formation, wherein the analysis includes distinguishing resonances in the transfer function as being resonances from the drill string or as being resonances from the formation.

13. The drill system according to claim 12 , wherein the operating parameters comprise one or more of one or more of a torque, a speed, a displacement, and an axial force.

14. The drill system according to claim 12 , wherein the one or more sensors comprise one or more accelerometers aligned with one or more directions.

15. The drill system according to claim 12 , wherein the plurality of prescribed input signals comprise a step input signal, a chirp signal, or a random white noise signal.

16. The drill system according to claim 12 , wherein the properties of the formation comprise one or more components of a three-dimensional stiffness/compliance matrix.

17. The drill system according to claim 12 , wherein the processor is further configured by software instructions to:
change the operating parameters based on the determined properties of the formation.

18. A specialized tool for a drill string, the specialized tool comprising:
a motive-force source coupled to the drill string, wherein the motive-force source operates a drill-bit of the drill string according to operating parameters;
one or more sensors coupled to the drill string, wherein the one or more sensors detect a mechanical response of the drill string; and
a computing device comprising a processor in communicat

Assignees

• Univ Texas

Inventors

• Torres-Verdin Carlos
• Shor Roman
• Van Oort Eric

Classifications

• E21B47/12

  Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling · CPC title

• E21B49/005

  Testing the nature of borehole walls or the formation by using drilling mud or cutting data · CPC title

• E21B49/003 Primary

  by analysing drilling variables or conditions (E21B49/005 takes precedence; systems specially adapted for monitoring a plurality of drilling variables or conditions E21B44/00) · CPC title