SYSTEMS AND METHODS FOR IMPROVING DRILLING EFFICIENCY

• US 20120217067A1
• Filed: 09/21/2010
• Published: 08/30/2012
• Est. Priority Date: 09/21/2009
• Status: Active Grant

• Current Assignee: National Oilwell Varco LP (NOV, Inc.)
• Original Assignee: National Oilwell Varco LP (NOV, Inc.)
• Inventors: Mebane, Robert Eugene III, Florence, Frederick Ray
• Granted Patent: US 8,939,234 B2
• Time in Patent Office: Days
• US Class Current: 175/57
• CPC Class Codes: E21B 44/02 Automatic control of the tool feed E21B44/005, E21B44/10 take precedence

Abstract

A method for drilling a borehole in an earthen formation comprises (a) providing a drilling system including a drillstring having a longitudinal axis, a bottom-hole assembly coupled to a lower end of the drillstring, and a drill bit coupled to a lower end of the bottom-hole assembly. In addition, the method comprises (b) rotating the drill bit at a rotational speed. Further, the method comprises (c) applying weight-on-bit to the drill bit and advancing the drill bit through the formation to form the borehole. Still further, the method comprises (d) pumping a drilling fluid down the drillstring to the drill bit. The drilling fluid has a flow rate down the drillstring. Moreover, the method comprises (e) oscillating the rotational speed of the drill bit during (c). The method also comprises (f) generating non-steady state conditions in the borehole during (e).

Claims

1. A method for drilling a borehole in an earthen formation, comprising:

(a) providing a drilling system including a drillstring having a longitudinal axis, a bottom-hole assembly coupled to a lower end of the drillstring, and a drill bit coupled to a lower end of the bottom-hole assembly;

(b) rotating the drill bit at a rotational speed;

(c) applying weight-on-bit to the drill bit and advancing the drill bit through the formation to form the borehole;

(d) pumping a drilling fluid down the drillstring to the drill bit, wherein the drilling fluid has a flow rate down the drillstring;

(e) oscillating the rotational speed of the drill bit during (c); and

(f) generating non-steady state conditions in the borehole during (e).

2. The method of claim 1, wherein the oscillations of the rotational speed of the drill bit have a period that is less than 10 seconds.

3. The method of claim 1, wherein the oscillations of the rotational speed of the drill bit have a random period or a random amplitude.

4. The method of claim 1, wherein the rotational speed of the drill bit is oscillated about a predetermined rotational speed set point.

5. The method of claim 4, wherein the rotational speed of the drill bit is maintained between a predetermined maximum rotational speed and a predetermined minimum rotational speed.

6. The method of claim 4, wherein the predetermined set point for the rotational speed varies with time.

7. The method of claim 1, further comprising:

(g) oscillating the axial speed or axial acceleration of the drill bit during (c).

8. The method of claim 2, wherein the axial speed of the drill bit is oscillated about a predetermined axial speed set point, and wherein the axial speed of the drill bit is maintained between a predetermined maximum axial speed and a predetermined minimum axial speed.

9. The method of claim 8, further comprising:

(h) oscillating the flow rate of the drilling fluid down the drillstring during (c).

10. The method of claim 9, wherein the oscillations of the rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid each have a period that is less than 10 seconds.

11. The method of claim 10, wherein the oscillations of the rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid each have a random period or a random amplitude.

12. The method of claim 4, wherein the rotation of the drillstring generates a first amount of energy, the axial movement of the drillstring generates a second amount of energy, and the flow of drilling fluid generates a third amount of energy;

and

wherein (f) comprises oscillating the sum of the first amount of energy, the second amount of energy, and the third amount of energy.

13. A method for maintaining non-steady state conditions in a borehole being drilled in an earthen formation, comprising:

(a) providing a drilling system including a drillstring having a longitudinal axis, a bottom-hole assembly coupled to a lower end of the drillstring, and a drill bit coupled to a lower end of the bottom-hole assembly;

(b) applying torque to the drill bit to rotate the drill bit, wherein the drill bit has a rotational speed and a rotational acceleration;

(c) applying weight-on-bit to the drill bit to advance the drill bit through the formation to form the borehole, wherein the drill bit has an axial speed and an axial acceleration;

(d) pumping a drilling fluid down the drillstring to the drill bit, wherein the drilling fluid has a flow rate down the drillstring and a pressure at an inlet of the drillstring;

wherein the rotational speed of the drill bit, the rotational acceleration of the drill bit, the axial speed of the drill bit, the axial acceleration of the drill bit, the flow rate of the drilling fluid down the drillstring, and the pressure of the drilling fluid at the inlet of the drillstring is each a drilling parameter;

(e) controllably oscillating two or more of the following drilling parameters during (c);

the rotational speed of the drill bit;

the rotational acceleration of the drill bit;

the axial speed of the drill bit;

the axial acceleration of the drill bit;

the flow rate of the drilling fluid down the drillstring; and

the pressure of the drilling fluid at the inlet of the drillstring.

14. The method of claim 13, wherein each controllably oscillated drilling parameter is oscillated about a predetermined set point.

15. The method of claim 14, wherein each controllably oscillated drilling parameters is oscillated between a predetermined maximum value and a predetermined minimum value.

16. The method of claim 14, wherein the oscillations of each controllably oscillated drilling parameters has a period less than 10 seconds.

17. The method of claim 16, wherein the oscillations of each controllably oscillated drilling parameters has a period less than 5 seconds.

18. A computer-readable storage medium comprising software that, when executed by a processor, causes the processor to:

(a) receive a predetermined maximum rotational speed for a drillstring, a predetermined minimum rotational speed for the drillstring, and a predetermined set point for the rotational speed of the drill bit;

(b) monitor the rotational speed of the drillstring;

(c) control the rotational speed of the drillstring; and

(d) oscillate the rotational speed of the drillstring about the predetermined set point for the rotational speed and between the predetermined maximum rotational speed and the predetermined minimum rotational speed.

19. The computer-readable storage medium of claim 18, wherein the software further causes the software to:

(e) receive a predetermined maximum axial speed for the drillstring, a predetermined minimum axial speed for the drillstring, and a predetermined set point for the axial speed of the drillstring;

(f) monitor the axial speed of the drillstring;

(g) control the axial speed of the drillstring; and

(h) oscillate the axial speed of the drillstring between the predetermined maximum axial speed and the predetermined minimum axial speed generally about the predetermined set point for the axial speed.

20. The computer-readable storage medium of claim 19, wherein the software further causes the software to:

(e) receive a predetermined maximum flow rate for a drilling fluid, a predetermined minimum flow rate for the drilling fluid, and a predetermined set point for the flow rate of the drilling fluid;

(f) monitor the flow rate of the drilling fluid;

(g) control the flow rate of the drilling fluid; and

(h) oscillate the flow rate of the drilling fluid between the predetermined maximum flow rate and the predetermined minimum flow rate generally about the predetermined set point for the flow rate.

21. The computer-readable storage medium of claim 20, wherein the software further causes the software to:

monitor a plurality of downhole conditions in a borehole during a drilling process;

oscillate the rotational speed of the drillstring, the axial speed of the drillstring, and the flow rate of the drilling fluid in response to the downhole conditions in the borehole.