Method of assaying downhole occurrences and conditions

• US 5,794,720 A
• Filed: 03/25/1996
• Issued: 08/18/1998
• Est. Priority Date: 03/25/1996
• Status: Expired due to Term

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Dresser Industries Incorporated (Halliburton Company)
• Inventors: Goldman, William A., Smith, Lee Morgan
• Primary Examiner(s): Dang, Hoang C.
• Application Number:
  US08/621,411
• Time in Patent Office: 876 Days
• Field of Search: 175/39, 175/40, 73/152.48, 73/152.47, 73/152.44, 73/152.45, 73/152.43
• US Class Current: 175/40
• CPC Class Codes: E21B 12/02 Wear indicators
• CPC Class Codes: E21B 2200/22 Fuzzy logic, artificial intelligence, neural networks or the like
• 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 44/005 Below-ground automatic control systems
• CPC Class Codes: E21B 49/003 by analysing drilling variables or conditions E21B49/005 takes precedence; systems specially adapted for monitoring a plurality of drilling variables or conditions E21B44/00

Abstract

A method of assaying work of an earth boring bit of a given size and design comprises the steps of drilling a hole with the bit from an initial point to a terminal point and recording the distance between the initial and terminal points. A plurality of electrical incremental actual force signals are generated, each corresponding to a force of the bit over a respective increment of the distance between the initial and terminal points. A plurality of electrical incremental distance signals are also generated, each corresponding to the length of the increment for a respective one of the incremental actual force signals. The incremental actual force signals and the incremental distance signals are processed to produce a value corresponding to the total work done by the bit in drilling from the initial point to the terminal point. Using such a basic work assay, a number of other downhole occurrences and/or conditions can be assayed. These include a wear rating for the type of bit, a determination of whether such a bit can drill a given interval of formation, and assessment of the abrasivity of rock drilled (which in turn can be used to modify the assays of other conditions and/or occurrences), a model of the wear of such a bit in current use, and a determination of the mechanical efficiency of the bit.

Claims

1. A method of assaying work of an earth boring bit of a given size and design, comprising the steps of:

drilling a hole with the bit from an initial point to a terminal point through a given formation interval;

recording the distance between the initial and terminal points;

generating a plurality of electrical incremental actual force signals each corresponding to a force of the bit over a respective increment of the distance between the initial and terminal points;

generating a plurality of electrical incremental distance signals, each corresponding to the length of the increment for a respective one of said incremental actual force signals;

processing the incremental actual force signals and the incremental distance signals to produce a value corresponding to the total work done by the bit in drilling from the initial point to the terminal point; and

using said value of total work done by the bit in the selection of a bit for drilling a hole in a formation analogous to said given formation interval.

2. The method of claim 1 comprising:

processing the incremental actual force signals and the incremental distance signals to produce an electrical weighted average force signal corresponding to a weighted average of the force exerted by the bit between the initial and terminal points; and

multiplying the weighted average force by the distance between the initial and terminal points to produce said total work value.

3. The method of claim 1 comprising;

processing the incremental actual force signals and the incremental distance signals to produce a respective electrical incremental actual work signal for each of said increments; and

cumulating said incremental actual work signals to produce an electrical total work signal corresponding to said total work value.

4. The method of claim 1 comprising:

developing a force/distance function by processing the incremental actual force signals and incremental distance signals, and integrating the function.

5. The method of claim 1 wherein bit vibrations cause the bit force to vary over the increment, and each incremental actual force signal corresponds to an average force of the bit for the respective increment.

6. The method of claim 1 wherein each incremental actual force signal is generated from electrical signals corresponding, respectively, to bit rotation speed, bit torque, and rate of bit penetration.

7. The method of claim 6 wherein each incremental actual force signal is also generated from electrical signals corresponding, respectively, to weight on bit and hydraulic impact force.

8. The method of claim 7 wherein each incremental actual force signal is also generated from an electrical signal corresponding to a lateral force applied to the bit while drilling the respective increment.

9. The method of claim 1 wherein each incremental actual force signal is generated from electrical signals corresponding, respectively, to bit torque and depth of cut per revolution.

10. The method of claim 1 further comprising:

determining a minimum work value for said given formation interval; and

comparing said minimum work value with said total work value to assay the efficiency of said bit.

11. A method of assaying work of an earth boring bit of a given size and design, comprising the steps of:

drilling a hole with the bit from an initial point to a terminal point;

recording the distance between the initial and terminal points;

generating a plurality of electrical incremental actual force signals each corresponding to a force of the bit over a respective increment of the distance between the initial and terminal points;

generating a plurality of electrical incremental distance signals, each corresponding to the length of the increment for a respective one of said incremental actual force signals;

processing the incremental actual force signals and the incremental distance signals to produce a value corresponding to the total work done by the bit in drilling from the initial point to the terminal point;

rating the wear for bits of said size and design, wherein a plurality of such holes are drilled with respective such bits, and respective total work determined for each of the bits;

generating a respective total work signal corresponding to the total work for each of said bits;

retrieving each of the bits from its respective hole after it has reached the respective terminal point;

measuring the wear of each bit after retrieval and generating a respective wear signal;

correlating the total work signal and the wear signal for each bit; and

extrapolating from the correlated total work and wear signals to generate a series of electrical signals corresponding to a continuous rated work relationship between work and wear for the bit size and design.

12. The method of claim 11 wherein said series of signals is transformed into visually perceptible form.

13. The method of claim 11 wherein bit vibrations cause the bit force to vary over the increment, and each incremental actual force signal corresponds to an average force of the bit for the respective increment.

14. The method of claim 13 further comprising:

generating a respective peak force signal corresponding to a maximum force of the bit over the respective increment;

determining a limit corresponding to a maximum allowable force for the rock strength of the respective increment; and

comparing a value corresponding to the peak force signal to the limit to assay possible excessive wear.

15. The method of claim 14 wherein, if the value corresponding to the peak force signal is greater than or equal to the limit, excluding the respective bit from those from which the rated work relationship signals are generated.

16. The method of claim 14 comprising producing an electrical limit signal corresponding to the limit and electronically comparing to the limit and peak force signals.

17. The method of claim 11 wherein the rated work relationship so generated includes a correlated maximum-wear-maximum-work point.

18. The method of claim 17 comprising determining whether a first bit of said size and design can drill a given interval of formation, comprising the further steps of:

generating at least two electrical bit efficiency signals, corresponding to the rock strengths in respective, successive increments of said interval;

processing the efficiency signals to produce respective electrical incremental predicted work signals corresponding to the work which would be done by the bit in drilling the respective increments;

processing the incremental predicted work signals to produce an electrical cumulative predicted work signal corresponding to the work which could be done by the bit drilling the increments;

comparing the sum of the lengths of the increments with the length of the interval;

if the sum of the lengths of the increments is less than the length of the interval, comparing the cumulative predicted work signal to an electrical signal corresponding to the work component of the maximum-wear-maximum-work point.

19. The method of claim 18 wherein the cumulative predicted work signal is less than the signal corresponding to the work component of the maximum-wear-maximum-work point, and further comprising:

so generating at least one further efficiency signal for a next successive interval;

adjusting the further efficiency signal for efficiency reductions due to work in prior increments;

so processing the adjusted further efficiency signal to produce a respective further incremental predicted work signal;

so processing all the incremental predicted work signals to produce a new cumulative predicted work signal corresponding to the work which could be done by the bit in drilling all the increments;

so comparing the sum of the lengths of the increments to the length of the interval.

20. The method of claim 19 wherein the sum of the lengths of the increments is less than the length of the interval, and further comprising:

comparing the new cumulative predicted work signal to the signal corresponding to the work component of the maximum-wear-maximum-work point.

21. The method of claim 20 wherein the new cumulative predicted work signal is less than the signal corresponding to the work component of the maximum-wear-maximum-work point, and further comprising repeating the steps of claim 19.

22. The method of claim 20 wherein the new cumulative predicted work signal is greater than or equal to the signal corresponding to the work component of the maximum-wear-maximum-work point, and further comprising repeating the steps of claim 18 for a new bit of the same size and design, but for a new interval less than the original interval by the sum of the lengths of the increments for the first bit.

23. The method of claim 19 wherein the sum of the lengths of the increments is greater than or equal to the length of the interval, and further comprising repeating the steps of claim 18 for a first bit of a different design.

24. The method of claim 23 further comprising, for each increment, generating a signal corresponding to the penetration rate for that increment by processing signals corresponding, respectively, to a limiting power for the rock strength in question, the efficiency for the increment in question, the rock strength in the increment in question, and the transverse cross-sectional area of the bit;

and, for each bit, processing the incremental penetration rate signals to produce a signal corresponding to the drilling time for the bit.

25. The method of claim 24 further comprising selecting, from the bit designs able to drill the interval in question, the bit design having the minimum cost per foot.

26. The method of claim 23 further comprising processing the new cumulative predicted work signal and the signal corresponding to the work component of the maximum-wear-maximum-work point to produce an electrical signal corresponding to the remaining useful life of the bit.

27. The method of claim 19 comprising, prior to the steps of claim 18, for at least one reference bit of the size and design of the first bit:

generating a respective electrical incremental minimum force signal corresponding to the minimum force theoretically required to fail the rock in each of said increments;

processing the incremental minimum force signals and the incremental distance signals for the reference bit to produce a respective incremental minimum work signal for each of said increments for the reference bit;

processing the incremental actual force signals and the incremental distance signals to produce a respective incremental actual work signal for each of said increments for the reference bit;

processing the incremental actual work signals and the incremental minimum work signals to produce a respective electrical incremental actual efficiency signal for each increment;

generating a plurality of electrical compressive strength signals corresponding to different rock compressive strengths;

correlating each compressive strength signal with one of said incremental actual efficiency signals corresponding to efficiency of the reference bit in an increment having the respective rock compressive strength; and

extrapolating from the correlated compressive strength and incremental actual efficiency signals for the reference bit to generate one series of electrical signals corresponding to a continuous efficiency-strength relationship for the bit size and design;

then, in performing the steps of claim 18 and 19;

using said one series to determine the magnitude of the bit efficiency signals so generated.

28. The method of claim 27 further comprising, prior to the steps of claim 18,

from said efficiency-strength relationship, determining a compressive strength cutoff above which the bit design should not attempt to drill, and

comparing the cutoff to the rock strengths in said given interval, and

proceeding with the steps of claim 18 for said first bit only if the rock strengths in said given interval are less than or equal to said cutoff.

29. The method of claim 27 further comprising, prior to the steps of claim 18;

from said incremental actual efficiency signals for the reference bit and said one series of signals, extrapolating at least one other series of electrical signals corresponding to a continuous relationship between cumulative work done and efficiency reduction due to wear for a respective one of the rock strengths in said given interval; and

in performing the steps of claims 18 and 19, using said other series to so adjust the efficiency signals.

30. The method of claim 18 further comprising:

assaying the abrasivity of the rock in the interval; and

further adjusting the incremental predicted work signals for increased wear due to abrasivity.

31. The method of claim 11 wherein each of said holes is drilled through a relatively non-abrasive medium, and further comprising determining the abrasivity of the rock drilled in a given section of another hole with another such bit by:

measuring the wear of said other bit after drilling said section of said other hole;

from said rated work relationship, selecting a value corresponding to the wear of the other bit and generating the corresponding electrical rated work signal;

determining the volume of the abrasive rock drilled in said section of said other hole and generating a corresponding electrical abrasive volume signal;

generating an electrical actual work signal corresponding to the work done by said other bit in drilling said section of said other hole; and

processing the actual work signal for said other bit, the rated work signal for said other bit, and the abrasive volume signal to produce an electrical abrasivity signal.

32. The method of claim 31 wherein the volume of abrasive rock drilled in said other hole is determined by processing electrical signals corresponding to lithological data.

33. The method of claim 32 wherein the lithological data are taken from logs from nearby wells.

34. The method of claim 32 wherein the lithological data are taken from said other hole by measurement while drilling techniques.

35. The method of claim 11 further comprising remotely modelling wear of such a bit in use in a current hole being drilled by:

a so generating respective incremental actual force signals and incremental distance signals for every increment drilled by said bit-in-use;

processing the incremental actual force signals and the incremental distance signals for the bit-in-use to produce a respective electrical incremental actual work signal for each increment drilled by said bit-in-use;

periodically cumulating said incremental actual work signals to produce an electrical current work signal corresponding to the work which has currently been done by the bit-in-use; and

using said rated work relationship, periodically transforming said current work signal to an electrical current wear signal indicative of the wear on the bit-in-use.

36. The method of claim 35 further comprising retrieving said bit-in-use when said current wear signal reaches a predetermined limit.

37. The method of claim 35 wherein, if a reference section of a reference hole, adjacent said current hole, drilled by a reference bit, contained relatively abrasive material:

measuring the wear of the reference bit;

from said rated work relationship, selecting a value corresponding to the wear of the reference bit and generating the corresponding electrical rated work signal;

determining the volume of the abrasive rock drilled in said reference section and generating a corresponding electrical abrasive volume signal;

generating an electrical actual work signal corresponding to the work done by the reference bit; and

processing the actual work signal for said reference bit, the rated work signal for said reference bit, and the abrasive volume signal to produce an electrical abrasivity signal; and

processing the abrasivity signal to adjust the current wear signal.

38. The method of claim 35 wherein vibrations of the bit in use cause the bit force to vary over the increment, and further comprising:

generating a respective peak force signal corresponding to a maximum force of the bit over the respective increment;

determining a limit corresponding to a maximum allowable force for the rock strength of the respective increment;

comparing a value corresponding to the peak force signal to the respective limit to assay possible wear in excess of that corresponding to the current wear signal.

39. The method of claim 36 comprising generating a respective electrical incremental actual efficiency signal, for each increment, corresponding to the efficiency of the bit under normal drilling conditions.

40. The method of claim 39 comprising:

generating a respective electrical incremental minimum force signal corresponding to the minimum force theoretically required to fail the rock in each of said increments;

processing the incremental minimum force signals and the incremental distance signals to produce a respective incremental minimum work signal for each of said increments;

processing the incremental actual force signals and the incremental distance signals to produce a respective incremental actual work signal for each of said increments; and

processing the incremental actual work signals and the incremental minimum work signals to produce the respective electrical incremental actual efficiency signal for each increment.

41. The method of claim 40 further comprising:

for an additional hole currently being drilled by an additional such bit, generating electrical real time incremental distance and force signals and so processing those signals to produce a series of electrical real time incremental work signals;

processing the real time incremental work signals with the respective incremental minimum work signals to produce a respective electrical real time incremental efficiency signal for each increment;

comparing the real time incremental efficiency signals to the respective incremental actual efficiency signals;

if the incremental real time efficiency and incremental actual efficiency signals diverge over a series of said increments, using the rate of divergence to determine whether the divergence indicates a drilling problem or an increase in rock abrasivity.

42. The method of claim 41 further comprising monitoring the rate of penetration while drilling, and using a decrease in the rate of penetration as a trigger to so compare the real time incremental efficiency and incremental actual efficiency signals.

43. The method of claim 40 further comprising:

generating a plurality of electrical compressive strength signals corresponding to different rock compressive strengths;

correlating each compressive strength signal with one of said incremental actual efficiency signals corresponding to actual efficiency of the bit in an increment having the respective rock compressive strength; and

extrapolating from the correlated compressive strength and incremental actual efficiency signals to generate one series of electrical signals corresponding to a continuous efficiency-strength relationship for the bit size and design.

44. The method of claim 43 further comprising:

from said efficiency-strength relationship, determining a compressive strength cutoff above which the bit design should not attempt to drill.

45. The method of claim 43 further comprising:

from said incremental actual efficiency signals and said one series of signals, extrapolating at least one other series of electrical signals corresponding to a continuous relationship between cumulative work done and efficiency reduction due to wear for a respective one of the rock strengths in said given interval.

46. The method of claim 39 comprising generating the actual efficiency signal by processing electrical signals corresponding respectively to:

depth of cut of the bit;

axial contact area of the bit;

weight on the bit;

torque;

in situ rock strength opposing torsional bit force;

in situ rock strength opposing axial bit force; and

total transverse cross-sectional area of the bit;

all for the respective increment.

47. The method of claim 39 comprising generating the actual efficiency signal by processing electrical signals corresponding respectively to:

in situ rock strength opposing torsional bit force;

depth of cut of the bit;

torque; and

total transverse cross-sectional area of the bit;

all for the respective increment.