Systems and methods for improving drilling efficiency

• US 8,939,234 B2
• Filed: 09/21/2010
• Issued: 01/27/2015
• 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
• Primary Examiner(s): MICHENER, BLAKE E
• Application Number:
  US13/497,490
• Publication Number:
  US 20120217067A1
• Time in Patent Office: 1,589 Days
• Field of Search: 175/57, 175/61, 175/62, 175/424
• 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) selecting a predetermined rotational speed set point value for the drill bit;

(f) selecting a predetermined maximum rotational speed that is greater than the set point value and a predetermined minimum rotational speed that is less than the set point value;

(g) oscillating the rotational speed of the drill bit asymmetrically and non-uniformly about the set point value during (c), wherein the oscillations of the rotational speed of the drill bit have a random period or a random amplitude between the predetermined maximum rotational speed and the predetermined minimum rotational speed;

(h) maintaining the rotational speed of the drill bit between the predetermined maximum rotational speed and the predetermined minimum rotational speed during (g); and

(i) generating non-steady state conditions in the borehole during (g).

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 predetermined rotational speed set point value varies with time.

4. The method of claim 1, further comprising:

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

5. The method of claim 4, wherein the axial speed of the drill bit is oscillated about a predetermined axial speed set point value, and wherein the axial speed of the drill bit is maintained between a predetermined maximum axial speed and a predetermined minimum axial speed.

6. The method of claim 5, further comprising:

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

7. The method of claim 6, 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.

8. The method of claim 7, 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 less than 10 seconds or a random amplitude between the predetermined maximum axial speed and the predetermined minimum axial speed.

9. The method of claim 4, wherein the rotation of the drill bit inputs a first amount of energy into the drilling system, the axial movement of the drill bit inputs a second amount of energy into the drilling system, and the flow of drilling fluid inputs a third amount of energy into the drilling system;

and

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

10. 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;

(e) selecting a first set point value for the rotational speed of the drill bit, a second set point value for the axial speed of the drill bit, and a third set point value for the flow rate of the drilling fluid down the drillstring;

(f) controllably oscillating rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid down the drillstring about the first set point value, the second set point value, and the third set point value, respectively, during (c)

wherein the oscillations in (f) of the rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid down the drillstring each have a random period less than 10 seconds and

wherein the rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid down the drillstring are each randomly oscillated in (f) between a predetermined maximum value and a predetermined minimum value.

11. The method of claim 10, wherein the oscillations in (f) of the rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid down the drillstring each have a period less than 5 seconds.

12. 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 drill bit, a predetermined minimum rotational speed for the drill bit, and a predetermined set point value for the rotational speed of the drill bit;

(b) monitor the rotational speed of the drill bit;

(c) control the rotational speed of the drill bit; and

(d) oscillate the rotational speed of the drill bit asymmetrically and non-uniformly about the predetermined set point value, the oscillations of the rotational speed of the drill bit having a random period or a random amplitude between the predetermined maximum rotational speed and the predetermined minimum rotational speed.

13. The computer-readable storage medium of claim 12, wherein the software further causes the software to:

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

(f) monitor the axial speed of the drill bit;

(g) control the axial speed of the drill bit; and

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

14. The computer-readable storage medium of claim 13, 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 value 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 value for the flow rate.

15. The computer-readable storage medium of claim 14, 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 drill bit, the axial speed of the drill bit, and

the flow rate of the drilling fluid in response to the downhole conditions in the borehole.