101 of FIG. 2 may determine a bit cleaning condition 240 indicating that the drill bit should be cleaned. The computing device 101 can transmit an alert indicating the bit cleaning condition 240. Additionally or alternatively, the computing device 101 can automatically adjust a flow rate of drilling fluid pumped downhole to flush the accumulated rock from the drill bit. In some examples, the computing device 101 may additionally or alternatively adjust the surface weight on bit, the surface RPMs, or other suitable drilling operational parameters for the drilling operation based on the bit cleaning condition 240 indicating that the drill bit should be cleaned. Other causes of deviation from the slope of region II may involve a change in subterranean formation, a drilling operational parameter change, system vibration caused by damage to the drill bit, and the like. The bit condition 224 can be determined based on changes in the t-w-d space.

Returning to FIG. 4, graph 404 and graph 406 depict the same bit-rock signature as graph 402. Graph 404 plots the TOB against the depth of cut (d) of the drill bit, and graph 406 plots the WOB against the depth of cut (including regions I, II, and III). For example, graph 404 The TOB, WOB, and depth of cut can be determined based on the drilling operational parameters 220 that are measured at the surface of the wellbore.

FIG. 5 depicts a graph 500 illustrating spatial distribution of bit conditions of a drilling system, according to one example of the present disclosure. Different bit conditions of a drill bit can be determined based on parameters of a bit-rock signature 222, which can include specific energy 226 and drilling strength 228. The specific energy 226 can be defined as E=t/d and the drilling strength 228 can be defined as S=w/d. When the drill bit is in a relatively good condition (e.g., sharp or workable, not dull), E and S may have a relatively similar order of magnitude. When a drill bit is dull or otherwise damaged, S may increase faster than E.

The bit condition in some examples can be determined based on the correlation between S and E. For example, the computing device 101 of FIG. 2 may determine a correlation coefficient 230 between the specific energy 226 and the drilling strength 228. In one example, the Pearson correlation coefficient r²may be used:

$r^{2} = \frac{\sum SE - n \bar{S} \bar{E}}{[\sqrt{n \sum S^{2} - {(\sum S)}^{2}}] [\sqrt{n \sum E^{2} - {(\sum E)}^{2}}]}$

- In other examples, any other suitable correlation coefficient may be used. The computing device 101 may determine that the bit condition 224 indicates dullness or damage to the drill bit when the correlation coefficient 230 exceeds a predetermined threshold.

The spatial distribution illustrated in FIG. 5 may be as follows: the computing device 101 may categorize the drill bit as having a sharp bit condition when E>500, E/S>1.6, d>3 mm, and there is a hard formation (e.g., as indicated by a specific energy exceeding a predetermined threshold). The computing device 101 may categorize the drill bit as having a workable bit condition when 1 mm<d≤3 mm or d≤1 mm, and E/S≥0.2. The computing device 101 may categorize the drill bit as having a dull bit condition when d≤1 and E/S<0.2. The dull bit condition can include instances where the drill bit dulls slowly over time and when the drill bit suddenly becomes dull (e.g., due to contacting a hard formation). Other spatial distributions may also be used to determine bit condition of a drill bit.

FIG. 6 illustrates a flow diagram 600 for determining real-time bit wear detection of a drilling system, according to one example of the present disclosure. The operations of the flow diagram 600 can be performed based on parameters determined as part of a bit-rock signature for a drilling operation. At block 602, if the depth of cut is greater than or equal to 1 mm, the flow diagram can continue to block 604, in which the drilling operation continues. Having a depth of cut greater than or equal to 1 mm can indicate that the drilling operation is being performed efficiently with a sharp or workable bit.

At block 604, if the depth of cut is less than 1 mm, the flow diagram 600 can continue to block 606 or block 614. At block 606, the correlation coefficient between the specific energy E of the subterranean formation (which is not influenced by bit condition) and the drilling strength S may be greater than a first predefined threshold such as 0.7. Having a relatively high correlation coefficient that is greater than the first threshold may indicate that the drill bit is in a sharp or workable condition and that the drilling operation is proceeding at a relatively efficient rate.

At block 608, the specific energy of the subterranean formation may be greater than a second predefined threshold, such as 500 MPa. Thus, the flow diagram 600 may continue to block 610, wherein the subterranean formation is determined to have a hard formation based on the specific energy being greater than the second threshold. If some or all of the conditions in blocks 604, 606, 608, and 610 are met, the flow diagram continues to block 612, in which the drilling operation can continue, as the drill bit may be in a sharp or workable condition.

At block 614, the correlation coefficient between the specific energy E of the subterranean formation and the drilling strength S may be less than a third predefined threshold such as 0.5. Having a relatively low correlation coefficient may indicate that the drill bit is in a relatively dull condition. At block 616, the scaled weight on bit w may be greater than a fourth threshold, such as 1000 N/m, for at least two stands of the drilling operation. At block 618, the ratio of drilling strength to specific energy may be greater than a fifth threshold, such as 5. If some or all of the conditions in blocks 604, 614, 616, and 618 are met, the flow diagram continues to block 620, in which a bit wear alarm may be triggered (e.g., output to a wellbore operator. Additionally or alternatively, the drilling operation may be automatically terminated or halted, and in some examples, the drill string may be lifted out of the wellbore to replace the worn drill bit.

FIG. 7 illustrates an example flow chart 700 of a process for determining real-time bit wear detection of a drilling system, according to one example of the present disclosure. The steps of FIG. 7 can be performed by the processing device 202 of FIG. 2. Other examples can include more steps, fewer steps, different steps, or a different order of steps than is shown in FIG. 7. The steps of FIG. 7 are described below with reference to the components of FIGS. 1-6 above.

At block 702, the processing device 202 can measure, during a drilling operation for drilling of a wellbore 102, at least one drilling operational parameter 220 using one or more sensors 134 positioned at (e.g., disposed above) a surface of the wellbore 102. Examples of the drilling operational parameters 220 can include hook load (e.g., weight on the hook 124 on which a drill string 112 and downhole tools, including the drill bit 120, hang), surface rotations per minute (RPMs) of the drill string 112, flow rate of drilling fluid pumped into the wellbore 102, weight on bit at surface of the wellbore 102, or any other suitable parameter that is measured at the surface of the wellbore 102. The drilling operational parameters 220 may not include measurements taken downhole or at the drill bit.

At block 704, the processing device 202 can generate, based on the at least one drilling operational parameter 220, a bit-rock signature 222 comprising at-bit parameters for a drill bit 120 used for drilling the wellbore 102. The bit-rock signature 222 can be determined while the drilling operation is ongoing. The bit-rock signature 222 can indicate the drilling response of the drill bit 120 performing the drilling operation (e.g., drilling into the subterranean formation 104). For example, to determine the bit-rock signature 222, the processing device 202 can determine a specific energy 226 of the subterranean formation 104 based on the drilling operational parameters 220. The processing device 202 can also determine a drilling strength 228 of the drilling operation based on the drilling operational parameters 220. The specific energy 226 and the drilling strength 228 can be determined from a depth of cut 232, a torque on bit 234, and a weight on bit 236. Each of the depth of cut 232, torque on bit 234, and weight on bit 236 (or any other at-bit parameters) can be determined from the drilling operational parameters 220, such as by graphing a hook load of the drill string 112 during a tag bottom event over time.

At block 706, the processing device 202 can determine, based on the at-bit parameters of the bit-rock signature 222 meeting one or more predefined conditions, a bit condition 224 of the drill bit 120. The bit condition 224 can be determined while the drilling operation is ongoing. Example bit conditions 224 can include a sharp condition, a workable condition, or a dull condition. A drill bit 120 with a dull condition may be incapable or otherwise inefficient in drilling the wellbore 102. In some cases, a drill bit 120 with a dull condition may cause damage to other downhole tools, such as by causing vibration in the tool string. The processing device 202 may determine that the drill bit 120 has a dull condition by determining that a value of one or more of the parameters included in the bit-rock signature 222 satisfies a predefined condition. For example, if a correlation coefficient 230 for the specific energy 226 and drilling strength 228 falls below a predefined value, the processing device 202 may determine that the drill bit 120 has a dull condition. Or, if one or more of the depth of cut 232, the torque on bit 234, or the weight on bit 236 have values that meet predefined conditions, the processing device 202 may determine that the drill bit 120 has a dull condition.

In some examples, the bit condition 2234 may include a bit cleaning condition 240. For example, the processing device 202 may determine, based on at least in part on one of the values of the depth of cut 232, the torque on bit 234, or the weight on bit 236, a bit cleaning condition 240 indicating that the drill bit 120 needs cleaning due to accumulated rock. The accumulated rock may be preventing the drill bit 120 from drilling at a desired ROP. Other conditions of the drill bit 120 may also be determined based on the bit-rock signature 222.

At block 708, the processing device 202 can output the bit condition 224 for use in modifying the drilling of the wellbore 102. The bit condition 224 can be output while the drilling operation is ongoing, so that real time adjustments can be made to the drilling operation. For example, if the bit condition 224 indicates that the drill bit 120 is dull or damaged, the processing device 202 can output an alert to a wellbore operator. Additionally or alternatively, the processing device 202 can automatically terminate, halt, or modify the drilling operation. For example, the processing device 202 may automatically adjust a weight on bit of the drill bit 120 based on the bit condition 224, such increasing the surface weight on bit if the slope of measured torque on bit 234 over weight on bit 236 has decreased but still has a positive value. In another example where the bit condition 224 indicates accumulated rock on the drill bit 120, the processing device 202 can automatically increase a flow rate of drilling fluid pumped into the wellbore 102. The increased drilling fluid can flush the accumulated rock off the drill bit 120, thus enabling the drill bit 120 increase ROP. Additionally or alternatively, the processing device 202 can adjust the surface weight on bit or the surface RPM to remove the accumulated rock off the drill bit 120.

In some aspects, system, method, and computer-readable medium for real-time bit wear detection based on surface data are provided according to one or more of the following examples:

As used below, any reference to a series of examples is to be understood as a reference to each of those examples disjunctively (e.g., “Examples 1-4” is to be understood as “Examples 1, 2, 3, or 4”).

Example 1 is a system comprising: a processing device; and a memory device that includes instructions executable by the processing device for causing the processing device to: measure, during a drilling operation for drilling of a wellbore, at least one drilling operational parameter using one or more sensors positioned at a surface of an operating rig for the wellbore; generate, during the drilling operation and based on the at least one drilling operational parameter, a bit-rock signature comprising at-bit parameters for a drill bit used for drilling the wellbore; determine, during the drilling operation and based on the at-bit parameters of the bit-rock signature meeting one or more predefined conditions, a bit condition of the drill bit; and output the bit condition for use in modifying the drilling of the wellbore.