METHODS AND SYSTEMS TO PREDICT ROTARY DRILL BIT WALK AND TO DESIGN ROTARY DRILL BITS AND OTHER DOWNHOLE TOOLS

• US 20110015911A1
• Filed: 09/28/2010
• Published: 01/20/2011
• Est. Priority Date: 08/08/2005
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Chen, Shilin
• Granted Patent: US 8,145,465 B2
• Time in Patent Office: Days
• US Class Current: 703/7
• CPC Class Codes: E21B 10/00 Drill bits specially adapted for deflecting the direction of boring E21B7/064; with means for collecting substances E21B27/00
• CPC Class Codes: E21B 44/00 Automatic control systems specially adapted for drilling operations, i.e. self-operating systems which function to carry out or modify a drilling operation without intervention of a human operator, e.g. computer-controlled drilling systems; Systems specially adapted for monitoring a plurality of drilling variables or conditions
• CPC Class Codes: E21B 7/04 Directional drilling

Abstract

Methods and systems may be provided to simulate forming a wide variety of directional wellbores including wellbores with variable tilt rates, relatively constant tilt rates, wellbores with uniform generally circular cross-sections and wellbores with non-circular cross-sections. The methods and systems may also be used to simulate forming a wellbore in subterranean formations having a combination of soft, medium and hard formation materials, multiple layers of formation materials, relatively hard stringers disposed throughout one or more layers of formation material, and/or concretions (very hard stones) disposed in one or more layers of formation material. Values of bit walk rate from such simulations may be used to design and/or select drilling equipment for use in forming a directional wellbore.

Claims

1. A computer implemented method for determining bit walk characteristics of a long gage rotary drill bit, including a gage pad having a first downhole end and a second uphole end comprising:

applying a set of drilling conditions to the bit including a rate of penetration along a bit rotational axis, at least one characteristic of an earth formation, and at least one characteristic of a wellbore formed by the rotary drill bit;

applying a steer rate to the bit by tilting the bit relative to a fulcrum point disposed between the downhole end and the uphole end of the gage pad;

simulating, for a time interval, drilling of the earth formation by the bit under the set of drilling conditions, including calculating a steer force applied to the bit, an associated walk force and an associated walk angle;

calculating a walk rate based at least on the steer force and the walk force;

repeating the simulating and the calculating successively for a predefined number of time intervals;

calculating an average walk rate and a walk angle for the bit over the simulated predefined number of time intervals; and

storing the calculated average walk rate and the calculated walk angle to a computer file as determined bit walk characteristics of the rotary drill bit.

2. The method of claim 1 wherein applying the at least one characteristic of the wellbore further comprises comparing interior dimensions of the wellbore with exterior dimensions of the rotary drill bit and other downhole tools associated with the rotary drill bit.

3. The method of claim 1 wherein calculating the walk rate further comprises comparing an interior configuration of the wellbore with an exterior configuration of the rotary drill bit and other downhole tools associated with the rotary drill bit.

4. The method as defined in claim 1, further comprising calculating the walk rate of the rotary bit, at time t, by:

Walk Rate=(Steer Rate/Steer Force)×

Walk Force

5. The method of claim 1 further comprising:

determining a bit walk direction of the rotary drill bit by calculating the average walk rate over the pre-defined number of time intervals under the applied set of drilling conditions where a magnitude of the applied steer rate is not equal to zero; and

determining walk characteristics based on if the average walk rate is negative, the bit walks left, and if the average walk rate is positive, the bit walks right.

6-15. -15. (canceled)

16. A method to prevent an undesired bit walk while forming a directional wellbore with a fixed cutter rotary drill bit having a downhole face and an associated sleeve having an uphole end comprising:

applying a set of drilling conditions to the fixed cutter rotary drill bit including at least bit rotational speed, rate of penetration along a bit rotational axis or bit axial force;

applying at least one characteristic of an earth formation and at least one characteristic of the directional wellbore formed by the fixed cutter rotary drill bit;

applying a steer rate to the fixed cutter rotary drill bit by tilting the bit relative to a fulcrum point used to direct the fixed cutter rotary drill bit to form the directional wellbore;

the fulcrum point disposed between the downhole face of the drill bit and the uphole end of the sleeve;

simulating, for a time interval, drilling the earth formation using the fixed cutter rotary drill bit under the set of drilling conditions, including calculating steer forces applied to the fixed cutter rotary drill bit and associated walk forces and walk angles;

calculating walk rates based at least on the steer forces and the walk forces;

repeating the simulating and the calculating walk rates successively for a predefined number of time intervals;

calculating an average walk rate of the bit over the simulated predefined number of time intervals;

if the simulations indicate undesired bit walk rates, modifying the design of the sleeve including at least a length of the sleeve, a width of a sleeve pad and an aggressiveness of an uphole portion of the sleeve to reduce friction forces between the uphole portions of the sleeve and adjacent portions of the wellbore when steering forces are applied to the fixed cutter rotary drill bit;

repeating the above steps until the resulting simulations indicate that bit walk characteristics of the associated rotary drill bit has been reduced to a satisfactory value; and

storing the design of the sleeve to a computer file.

17. The method of claim 16 further comprising manufacturing the fixed cutter rotary drill bit and the associated sleeve with the design features that correspond to the design of the sleeve stored in the computer file.

18. A computer implemented method for determining bit walk characteristics of a rotary drill bit and an associated sleeve comprising:

applying a set of drilling conditions to the bit including at least bit rotational speed, bit axial force, at least one characteristic of an earth formation, and characteristic of a wellbore formed by the rotary drill;

applying a steer rate to the bit by tilting the bit around a fulcrum point disposed on a sleeve located above the bit face, wherein the fulcrum point is defined as a contact between an exterior portion of the sleeve and adjacent portion of wellbore;

simulating, for a time interval, drilling of the earth formation by the bit under the set of drilling conditions, including calculating a steer force applied to the bit and an associated walk force;

calculating a walk rate based at least on the steer force and the walk force;

repeating the simulating successively for a predefined number of time intervals; and

calculating average walk characteristics of the bit over the simulated time interval; and

storing the design of the sleeve to a computer file.

19-26. -26. (canceled)

27. The rotary drill bit of claim 27, further comprising the rotary drill bit having a bit face prepared by a process wherein calculating an average bit walk rate further comprises:

applying a set of drilling conditions to the bit including at least bit rotational speed, hole size and rate of penetration along a bit rotational axis and at least one characteristic of an earth formation;

applying a steer rate to the bit, wherein applying the steer rate includes tilting the bit around a fulcrum point disposed between a top section of the bit gage and the bit face;

simulating, for a time interval, drilling of the earth formation by the bit under the set of drilling conditions, including calculating a steer moment applied to the bit and an associated walk moment;

calculating a walk rate based on the bit steer rate, the steer moment, and the walk moment;

repeating simulating drilling the earth formation for another time interval, and recalculating the steer moment, the walk moment and walk rate;

repeating the simulating successively for a predefined number of time intervals;

calculating an average walk rate of the bit using an average steer moment and an average walk moment over the simulated time interval; and

storing the calculated average walk rate and the set of drilling conditions to a computer file.

28. (canceled)