# US 5,704,436 A · Method of regulating drilling conditions applied to a well bit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,704,436 A - Document ID: US5704436A - Status: Granted - Kind: A - Application number: 08/621,414 - Filed: 1996-03-25 - Granted: 1998-01-06 - Earliest claimed: 1996-03-25 - Assignees: Dresser Industries, Inc. - Inventors: Lee Morgan Smith; William A. Goldman - Web page: https://patentgrep.com/patent/US5704436A ## CPC - E21B 12/02: Wear indicators - 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 - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS ## Abstract A method of regulating drilling conditions applied to a given well bit comprises assaying the compressive strength of the formation in an interval to be drilled by said bit. Wear of critical bit structure of the same size and design as in said given bit and which structure has drilled material of approximately the same compressive strength as that so assayed, is analyzed along with respective drilling data for the worn structure. From said analysis, a power limit for the respective compressive strength, above which power limit excessive wear is likely to occur is determined. Drilling conditions, such as rotary speed and weight-on-bit, at which the given bit is operated are regulated to maintain a desired operating power less than or equal to the power limit. Where several feasible rotary speed/weight-on-bit combinations may result in the desired operating power, these conditions are optimized. ## Claims ### Claim 1 A method of regulating drilling conditions applied to a given well bit, comprising the steps of: assaying the compressive strength of the formation in an interval to be drilled by said bit; analyzing wear of critical bit structure of the same size and design as in said given bit and which structure has drilled material of approximately the same compressive strength as that so assayed, along with respective drilling data for the worn structure; from said analysis determining a power limit for the respective compressive strength, above which power limit undesirable bit wear is likely to occur; and regulating drilling conditions at which said given bit is operated to maintain a desired operating power less than or equal to said power limit. ### Claim 2 (depends on 1) The method of claim 1 wherein a plurality of such structures and respective drilling data are so analyzed; further comprising generating from said analyses a first type series of correlated pairs of electrical signals, the two signals of each such pair corresponding, respectively, to wear rate and operating power for a respective one of said structures; and wherein said power limit is generated from said signals of said first type series. ### Claim 3 (depends on 2) The method of claim 2 wherein at least one of said structures is a separate part of a size and design used in said given bit and is so analyzed under laboratory conditions. ### Claim 4 (depends on 2) The method of claim 2 wherein at least one of said structures is a complete bit of the same size and design as said given bit and is so worn in field drilling. ### Claim 5 (depends on 2) The method of claim 2 wherein said drilling conditions are so regulated to maintain said desired operating power less than but about as close as reasonably possible to said power limit. ### Claim 6 (depends on 2) The method of claim 2 wherein: said drilling conditions include conditions applied to said given bit; bit vibrations cause forces transmitted to the formation by the bit to vary over small increments of said interval; and the applied conditions are so regulated with reference to the peak transmitted forces. ### Claim 7 (depends on 2) The method of claim 2 wherein the conditions so regulated are rotary speed and weight-on-bit. ### Claim 8 (depends on 7) The method of claim 7 further comprising generating a second type series of correlated pairs of electrical signals, the respective signals of each pair corresponding to a rotary speed value and a weight-on-bit value, wherein the rotary speed and weight-on-bit values of each pair theoretically result in a power corresponding to the power limit; and wherein said bit is operated at a rotary speed and weight-on-bit corresponding to one of said pairs of signals in said second type series. ### Claim 9 (depends on 8) The method of claim 8 further comprising determining a rotary speed limit for said power limit above which substantially disadvantageous bit movement characteristics are likely to occur, and so operating said bit at a rotary speed below said rotary speed limit. ### Claim 10 (depends on 9) The method of claim 9 further comprising determining a weight-on-bit limit for said power limit above which substantially disadvantageous bit movement characteristics are likely to occur, and so operating said bit at a weight-on-bit below said weight-on-bit limit. ### Claim 11 (depends on 10) The method of claim 10 further comprising: determining a marginal rotary speed for said power limit, less than said rotary speed limit, above which undesirable bit movement characteristics are likely to occur; determining a marginal weight-on-bit for said power limit, less than said weight-on-bit limit, above which undesirable bit movement characteristics are likely to occur; and so operating said bit at a rotary speed less than or equal to said marginal rotary speed, and at a weight-on-bit less than or equal to said marginal weight-on-bit. ### Claim 12 (depends on 11) The method of claim 11 further comprising so operating said bit at such rotary speed and weight-on-bit about as close as reasonably possible to said marginal weight-on-bit. ### Claim 13 (depends on 12) The method of claim 12 further comprising determining a weight-on-bit and rotary speed combination at which a maximum depth of cut is achieved; and operating said bit at a weight-on-bit close or equal to the lesser of the weight-on-bit corresponding to said maximum depth of cut or the marginal weight-on-bit. ### Claim 14 (depends on 10) The method of claim 10 further comprising: determining a marginal rotary speed for said power limit, less than said rotary speed limit, above which undesirable bit movement characteristics are likely to occur; determining a marginal weight-on-bit for said power limit, less than said weight-on-bit limit, above which undesirable bit movement characteristics are likely to occur; determining a weight-on-bit for said power limit which produces a maximum depth of cut for the bit; and so operating said bit at a rotary speed less than or equal to said marginal rotary speed, and at a weight-on-bit close or equal to the lesser of said marginal weight-on-bit and said weight-on-bit for the maximum depth of cut. ### Claim 15 (depends on 8) The method of claim 8 further comprising determining a weight-on-bit limit for said power limit above which substantially disadvantageous bit movement characteristics are likely to occur, and so operating said bit at a weight-on-bit below said weight-on-bit limit. ### Claim 16 (depends on 8) The method of claim 8 further comprising so generating a plurality of signal series of the second type, each for a different amount of wear, and periodically increasing the weight-on-bit as said bit wears in accord with the appropriate series of the second type. ### Claim 17 (depends on 16) The method of claim 16 further comprising altering the rotary speed as the weight-on-bit is so increased. ### Claim 18 (depends on 17) The method of claim 17 further comprising measuring or modeling wear of said bit in real time. ### Claim 19 (depends on 8) The method of claim 8 wherein said compressive strength assay includes a plurality of formation layers of different compressive strengths, and further comprising: so generating respective such first and second type series of signals for each such compressive strength; monitoring the progress of said bit through the formation; and periodically altering the operation of said bit in accord with the respective series of signals for the compressive strength of the formation currently being drilled by said bit. ### Claim 20 (depends on 1) The method of claim 1 wherein said compressive strength is so assayed by modeling in real time while drilling said interval with said bit.