DRILL BIT DESIGN METHOD BASED ON ROCK CRUSHING PRINCIPLE WITH LOCAL VARIABLE STRENGTH

Abstract

The invention discloses a drill bit design method based on rock crushing principle with local variable strength, including: drill bit is divided into local crushing feature regions; strength mode factors of the local crushing feature regions are calculated; a difference among strength mode factors of the local crushing feature regions is obtained to obtain a vector sum of horizontal cutting forces of the drill bit tooth corresponding to the same group of cutting tooth on the drill bit; treating the difference among the strength mode factors of the local crushing feature region as a target control condition for drill bit design. Based on the rock crushing principle with local variable strength, after dividing the symmetrical cutting tooth into groups, the strength variation factors of the symmetrical position are adjusted and balanced, so that the rock crushing strength of different local crushing feature regions can be changed in a targeted manner.

Claims

1. A drill bit design method based on rock crushing principle with local variable strength, comprising steps of: Step S1: selecting a type of a drill bit, a number of blades and a type of a drill bit tooth, and using a processor for dividing the drill bit into a local crushing feature region as a whole according to a drill bit local crushing feature region division method, wherein the local crushing feature region comprises a single crushing region and a mixed crushing region; Step S2: using the processor for establishing a relationship among a dynamic rock uniaxial compressive strength, a static rock uniaxial compressive strength and a dynamic loading strain rate of a load; establishing a relationship among a dynamic rock tensile strength, a static rock tensile strength and the dynamic loading strain rate of the load; using the processor for establishing a relationship among a dynamic rock shear strength, a static rock shear strength and the dynamic loading strain rate of the load; Step S3: using the processor for determining tooth distribution parameters preliminarily according to drill bit tooth overall mechanics balance conditions, and calculating bottom hole rock strength variation factors of the local crushing feature region and strength mode factors of the local crushing feature region according to the tooth distribution parameters of the drill bit and the relationship among the dynamic rock uniaxial compressive strength, the static rock uniaxial compressive strength and a dynamic loading strain rate of the load, the relationship among the dynamic rock tensile strength, the static rock tensile strength and the dynamic loading strain rate of the load and the relationship among the dynamic rock shear strength, the static rock shear strength and the dynamic loading strain rate of the load established in the Step S2; Step S4: using the processor for controlling a difference among the strength mode factors of the single crushing region within 20% and controlling a difference among the strength mode factors of the mixed crushing region within 25% by adjusting drill bit parameters and regulating a difference among the strength mode factors of the local crushing feature region in the Step S3; Step S5: using the processor for treating the difference among the strength mode factors of the local crushing feature region obtained in the Step S4 as a target control condition for drill bit design, wherein the drill bit design is completed if the target control condition for drill bit design is met, and the drill bit tooth distribution parameters are continued to be adjusted to meet the target control condition for drill bit design to complete the drill bit design if the target control condition for drill bit design is not met.

2. The drill bit design method based on rock crushing principle with local variable strength according to claim 1, wherein in the Step S1, the type of the drill bit comprises a PDC drill bit and a PDC-roller-cone compact drill bit; the number of blades comprises a PDC drill bit with 4 blades, a PDC drill bit with 5 blades, a PDC drill bit with 6 blades, a PDC-roller-cone compact drill bit with 4 blades and a PDC-roller-cone compact drill bit with 6 blades, wherein the PDC-roller-cone compact drill bit with 4 blades is a roller-cone with 2 blades plus PDC with 2 blades, and the PDC-roller-cone compact drill bit with 6 blades comprises a roller-cone with 2 blades plus PDC with 4 blades and a roller-cone with 3 blades plus PDC with 3 blades; the type of the drill bit tooth comprises a plane cutting tooth and a tapered cutting tooth.

3. The drill bit design method based on rock crushing principle with local variable strength according to claim 1, wherein in the Step S1, the drill bit tooth local crushing feature region division method specifically comprises: using the processor for classifying symmetrical blades of the PDC drill bit with an even number of blades into one group, and dividing the drill bit tooth of the same type in each group of blades into the local crushing feature region; dividing the drill bit tooth of the same type of the PDC drill bit with an odd number of blades into the local crushing feature region; using the processor for classifying PDC blades of the PDC-roller-cone compact drill bit into the same group, dividing the roller-cone blades into the same group, and dividing the drill bit tooth of the same type in each group into the local crushing feature region.

4. The drill bit design method based on rock crushing principle with local variable strength according to claim 1, wherein in the Step S1, the single crushing region comprises a compressive crushing region, a shear crushing region and a tensile crushing region; the mixed crushing region is divided into a compressive-shear crushing region, a shear-tensile crushing region and a compressive-tensile crushing region.

5. The drill bit design method based on rock crushing principle with local variable strength according to claim 1, wherein in the Step S2, the method of using the processor for establishing the relationship among the dynamic rock uniaxial compressive strength, the static rock uniaxial compressive strength and the dynamic loading strain rate of the load specifically comprises: using the processor for measuring the dynamic rock uniaxial compressive strength by a split Hopkinson pressure bar (SHPB) rock mechanics experiment machine, and performing a curve fit on a ratio between the dynamic rock uniaxial compressive strength and the static rock uniaxial compressive strength and the dynamic loading strain rate of the load, so as to finally establish the relationship among the dynamic rock uniaxial compressive strength, the static rock uniaxial compressive strength and the dynamic loading strain rate of the load, which is specifically expressed as follows: $\frac{{\sigma }_{ucd}}{{\sigma }_{uc}}=\{\begin{array}{c}{a}_1{\dot{\epsilon }}^{1/\left(1+n_c\right)}\left(\dot{\epsilon }<{\dot{\epsilon }}^{*}\right)\\ a_2{\dot{\epsilon }}^{1/n}\left(\dot{\epsilon }\ge {\dot{\epsilon }}^{*}\right)\end{array}$ in the Step S2, the method of using the processor for establishing the relationship among the dynamic rock tensile strength, the static rock tensile strength and the dynamic loading strain rate of the load specifically comprises: measuring the dynamic rock tensile strength by the SHPB rock mechanics experiment machine, and performing a curve fit on a ratio between the dynamic rock tensile strength and the static rock tensile strength and the dynamic loading strain rate of the load, so as to finally establish a relationship among the dynamic rock tensile strength, the static rock tensile strength and the dynamic loading strain rate of the load, which is specifically expressed as follows: $\frac{{\sigma }_{td}}{{\sigma }_t}=\{\begin{array}{c}{b}_1{\dot{\epsilon }}^{1/\left(1+n_c\right)}\left(\dot{\epsilon }<{\dot{\epsilon }}^{*}\right)\\ b_2{\dot{\epsilon }}^{1/n}\left(\dot{\epsilon }\ge {\dot{\epsilon }}^{*}\right)\end{array}$ in the Step S2, the method of using the processor for establishing the relationship among the dynamic rock shear strength, the static rock shear strength and the dynamic loading strain rate of the load specifically comprises: measuring the dynamic rock shear strength by the SHPB rock mechanics experiment machine, and performing a curve fit on a ratio between the dynamic rock shear strength and the static rock shear strength and the dynamic loading strain rate of the load, so as to finally establish a relationship among the dynamic rock shear strength, the static rock shear strength and the dynamic loading strain rate of the load, which is specifically expressed as follows: $\frac{{\sigma }_{sd}}{{\sigma }_s}=\{\begin{array}{c}{c}_1{\dot{\epsilon }}^{1/\left(1+n_c\right)}\left(\dot{\epsilon }<{\dot{\epsilon }}^{*}\right)\\ c_2{\dot{\epsilon }}^{1/n}\left(\dot{\epsilon }\ge {\dot{\epsilon }}^{*}\right)\end{array}$ wherein a.sub.1, a.sub.2, b.sub.1, b.sub.2, c.sub.1, c.sub.2, n, n.sub.c are fit coefficients, dimensionless; σ.sub.uc is the static rock uniaxial compressive strength, MPa; σ.sub.t is the static rock tensile strength, MPa; σ.sub.s is the static rock shear strength, MPa; σ.sub.ucd is the dynamic rock uniaxial compressive strength, MPa; σ.sub.td is the dynamic rock tensile strength, MPa; σ.sub.sd is the dynamic rock shear strength, MPa; {dot over (ε)} is the dynamic loading strain rate of the load, s.sup.−1; {dot over (ε)}* is the dynamic loading critical strain rate of the load, s.sup.−1.

6. The drill bit design method based on rock crushing principle with local variable strength according to claim 5, wherein a calculation method of the dynamic loading strain rate of the load {dot over (ε)} in the process of crushing rocks with the drill bit tooth is expressed as follows: $\stackrel{.}{\epsilon }=\frac{1.4v_c\sin \gamma }{d\sin \left(\gamma +\omega \right)}$ wherein {dot over (ε)} is the dynamic loading strain rate of the load, s.sup.−1; v.sub.c is the cutting tooth speed, mm/s; d is the cutting depth, mm; γ is the drill bit tooth caster angle, rad; ω is the scrap forming-compaction transition angle, rad; the cutting speed v.sub.ci of the ith main cutting tooth on the drill bit is expressed as follows: $v_{ci}=\frac{\pi r_{i}RP{M}_n}{30}$ wherein r.sub.i is a distance from a position where the ith main cutting tooth on the drill bit is located to an axis of the drill bit, m; RPM is the rotating speed of the cutting tooth on the drill bit, r/min; v.sub.ci is the cutting speed of the ith cutting tooth on the drill bit, m/s.

7. The drill bit design method based on rock crushing principle with local variable strength according to claim 1, wherein in the Step S3, the tooth distribution parameters comprise the number of drill bit tooth, a diameter of each of the drill bit tooth, a caster angle of each of the drill bit tooth, and a distance from a position where each of the main cutting tooth is located to the axis of the drill bit.

8. The drill bit design method based on rock crushing principle with local variable strength according to claim 1, wherein in the Step S3, the method of calculating bottom hole rock strength variation factors of the local crushing feature region specifically comprises: using the processor for obtaining a relationship between the bottom hole rock strength variation factors and the drill bit tooth distribution parameters corresponding to each of the main cutting tooth by the curve fit method according to the relationship among the dynamic rock uniaxial compressive strength, the static rock uniaxial compressive strength and the dynamic loading strain rate of the load, the relationship among the dynamic rock tensile strength, the static rock tensile strength and the dynamic loading strain rate of the load and the relationship among the dynamic rock shear strength, the static rock shear strength and the dynamic loading strain rate of the load obtained in the Step S2, which is specifically expressed as follows: $\frac{{\sigma }_{ucdi}}{{\sigma }_{uc}}=\{\begin{array}{c}{a}_{1i}{v}_{ci}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/\left(1+n_{ci}\right)}\left(\dot{\epsilon }<{\dot{\epsilon }}^{*}\right)\\ a_{2i}{v}_{ci}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/n_i}\left(\dot{\epsilon }\ge {\dot{\epsilon }}^{*}\right)\end{array}$ $\frac{{\sigma }_{sdi}}{{\sigma }_s}=\{\begin{array}{c}{b}_{1i}{v}_{ci}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/\left(1+n_{ci}\right)}\left(\dot{\epsilon }<{\dot{\epsilon }}^{*}\right)\\ b_{2i}{v}_{ci}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/n_i}\left(\dot{\epsilon }\ge {\dot{\epsilon }}^{*}\right)\end{array}$ $\frac{{\sigma }_{tdi}}{{\sigma }_t}=\{\begin{array}{c}{c}_{1i}{v}_{ci}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/\left(1+n_{ci}\right)}\left(\dot{\epsilon }<{\dot{\epsilon }}^{*}\right)\\ c_{2i}{v}_{ci}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/n_i}\left(\dot{\epsilon }\ge {\dot{\epsilon }}^{*}\right)\end{array}$ wherein a.sub.1i, a.sub.2i, b.sub.1i, b.sub.2i, c.sub.1i, c.sub.2i, n.sub.1, n.sub.ci are fit coefficients of the strength variation factor expression corresponding to the ith cutting tooth on the drill bit, dimensionless; σ.sub.ucdi is the dynamic uniaxial compressive strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, MPa; $\frac{{\sigma }_{ucdi}}{{\sigma }_{uc}}$ is the ratio between the dynamic uniaxial compressive strength and the static uniaxial compressive strength in the process of dynamically crushing rocks of the i th cutting tooth on the drill bit, compressive strength variation factors for short, dimensionless; σ.sub.sdi is the dynamic shear strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, MPa; $\frac{{\sigma }_{sdi}}{{\sigma }_s}$ is the ratio between the dynamic shear strength and the static shear strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, shear strength variation factors for short, dimensionless; σ.sub.tdi is the dynamic tensile strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, MPa; $\frac{{\sigma }_{tdi}}{{\sigma }_t}$ is the ratio between the dynamic tensile strength and the static tensile strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, tensile strength variation factors for short, dimensionless; σ.sub.uc is the static rock uniaxial compressive strength, MPa; σ.sub.t is the static rock tensile strength, MPa; σ.sub.s is the static rock shear strength, MPa; v.sub.ci is the cutting speed of the ith cutting tooth on the drill bit, m/s; d is the cutting depth, mm; γ is the caster angle of the drill bit tooth, rad; ω is the scrap forming-compaction transition angle, rad; {dot over (ε)}* is the dynamic loading critical strain rate of the load, s.sup.−1.

9. The drill bit design method based on rock crushing principle with local variable strength according to claim 1, wherein in the Step S3, the method of calculating the strength mode factors of the local crushing feature region comprises: when the local crushing feature region is the compressive crushing region: $\mathrm{LSC}=\mathrm{Max}\left\{\begin{array}{ccccc}\frac{{\sigma }_{\mathrm{ucd}1}}{{\sigma }_{uc}}.Math.& \frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{uc}}.Math.& \frac{{\sigma }_{\mathrm{ucd}3}}{{\sigma }_{uc}}& .Math.& \frac{{\sigma }_{\mathrm{ucdk}}}{{\sigma }_{uc}}\end{array}\right\}-\mathrm{Min}\left\{\begin{array}{ccccc}\frac{{\sigma }_{\mathrm{ucd}1}}{{\sigma }_{uc}}.Math.& \frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{uc}}.Math.& \frac{{\sigma }_{\mathrm{ucd}3}}{{\sigma }_{uc}}& .Math.& \frac{{\sigma }_{\mathrm{ucdk}}}{{\sigma }_{uc}}\end{array}\right\}$ when the local crushing feature region is the shear crushing region: $\mathrm{LSS}=\mathrm{Max}\left\{\frac{{\sigma }_{sd1}}{{\sigma }_s}.Math.\frac{{\sigma }_{sd2}}{{\sigma }_s}.Math.\frac{{\sigma }_{sd3}}{{\sigma }_s}.Math.\frac{{\sigma }_{sd1}}{{\sigma }_s}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{sd1}}{{\sigma }_s}.Math.\frac{{\sigma }_{sd2}}{{\sigma }_s}.Math.\frac{{\sigma }_{sd3}}{{\sigma }_s}.Math.\frac{{\sigma }_{sd1}}{{\sigma }_s}\right\}$ when the local crushing feature region is the tensile crushing region: $\mathrm{LST}=\mathrm{Max}\left\{\frac{{\sigma }_{td1}}{{\sigma }_t}.Math.\frac{{\sigma }_{td2}}{{\sigma }_t}.Math.\frac{{\sigma }_{td3}}{{\sigma }_t}.Math.\frac{{\sigma }_{tdn}}{{\sigma }_t}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{td1}}{{\sigma }_t}.Math.\frac{{\sigma }_{td2}}{{\sigma }_t}.Math.\frac{{\sigma }_{td3}}{{\sigma }_t}.Math.\frac{{\sigma }_{tdn}}{{\sigma }_t}\right\}$ when the local crushing feature region is the compressive-shear crushing region: $\mathrm{LSCS}=\mathrm{Max}\left\{\frac{{\sigma }_{ucd1}}{{\sigma }_{uc}}-\frac{{\sigma }_{sd1}}{{\sigma }_s}.Math.\frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{uc}}-\frac{{\sigma }_{sd2}}{{\sigma }_s}.Math.\frac{{\sigma }_{ucd3}}{{\sigma }_{uc}}-\frac{{\sigma }_{sd3}}{{\sigma }_s}.Math....\frac{{\sigma }_{ucdk}}{{\sigma }_{uc}}-\frac{{\sigma }_{sdm}}{{\sigma }_s}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{ucd1}}{{\sigma }_{uc}}-\frac{{\sigma }_{sd1}}{{\sigma }_s}.Math.\frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{uc}}-\frac{{\sigma }_{sd2}}{{\sigma }_s}.Math.\frac{{\sigma }_{ucd3}}{{\sigma }_{uc}}-\frac{{\sigma }_{sd3}}{{\sigma }_s}.Math....\frac{{\sigma }_{ucdk}}{{\sigma }_{uc}}-\frac{{\sigma }_{sdm}}{{\sigma }_s}\right\}$ when the local crushing feature region is the shear-tensile crushing region: $\mathrm{LSST}=\mathrm{Max}\left\{\frac{{\sigma }_{sd1}}{{\sigma }_s}-\frac{{\sigma }_{td1}}{{\sigma }_t}.Math.\frac{{\sigma }_{sd2}}{{\sigma }_s}-\frac{{\sigma }_{td2}}{{\sigma }_t}.Math.\frac{{\sigma }_{sd3}}{{\sigma }_s}-\frac{{\sigma }_{td3}}{{\sigma }_t}.Math....\frac{{\sigma }_{\mathrm{sdj}}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{tdj}}}{{\sigma }_t}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{sd1}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{td}1}}{{\sigma }_t}.Math.\frac{{\sigma }_{sd2}}{{\sigma }_s}-\frac{{\sigma }_{td2}}{{\sigma }_t}.Math.\frac{{\sigma }_{sd3}}{{\sigma }_s}-\frac{{\sigma }_{td3}}{{\sigma }_t}.Math....\frac{{\sigma }_{\mathrm{sdj}}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{tdj}}}{{\sigma }_t}\right\}$ when the local crushing feature region is the compressive-tensile crushing region: $\mathrm{LSCT}=\mathrm{Max}\left\{\frac{{\sigma }_{ucd1}}{{\sigma }_{uc}}-\frac{{\sigma }_{td1}}{{\sigma }_t}.Math.\frac{{\sigma }_{ucd2}}{{\sigma }_{uc}}-\frac{{\sigma }_{td2}}{{\sigma }_t}.Math.\frac{{\sigma }_{ucd3}}{{\sigma }_{uc}}-\frac{{\sigma }_{td3}}{{\sigma }_t}.Math....\frac{{\sigma }_{ucdq}}{{\sigma }_{uc}}-\frac{{\sigma }_{tdq}}{{\sigma }_t}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{ucd1}}{{\sigma }_{uc}}-\frac{{\sigma }_{td1}}{{\sigma }_t}.Math.\frac{{\sigma }_{ucd2}}{{\sigma }_{uc}}-\frac{{\sigma }_{td2}}{{\sigma }_t}.Math.\frac{{\sigma }_{ucd3}}{{\sigma }_{uc}}-\frac{{\sigma }_{td3}}{{\sigma }_t}.Math....\frac{{\sigma }_{ucdq}}{{\sigma }_{uc}}-\frac{{\sigma }_{tdq}}{{\sigma }_t}\right\}$ wherein LSC is the strength mode factor when the local crushing feature region is the compressive crushing region, dimensionless; LSS is the strength mode factor when the local crushing feature region is the shear crushing region, dimensionless; LST is the strength mode factor when the local crushing feature region is the tensile crushing region, dimensionless; LSCS is the strength mode factor when the local crushing feature region is the compressive-shear crushing region, dimensionless; LSST is the strength mode factor when the local crushing feature region is the shear-tensile crushing region, dimensionless; LSCT is the strength mode factor when the local crushing feature region is the compressive-tensile crushing region, dimensionless; k is the number of the cutting tooth when the local crushing feature region is the compressive crushing region, dimensionless; l is the number of the cutting tooth when the local crushing feature region is the shear crushing region, dimensionless; n is the number of the cutting tooth when the local crushing feature region is the tensile crushing region, dimensionless; m is the number of the cutting tooth when the local crushing feature region is the compressive-shear crushing region, dimensionless; j is the number of the cutting tooth when the local crushing feature region is the shear-tensile crushing region, dimensionless; q is the number of the cutting tooth when the local crushing feature region is the compressive-tensile crushing region, dimensionless; σ.sub.uc is the static rock uniaxial compressive strength, MPa; σ.sub.t is the static rock tensile strength, MPa; σ.sub.s is the static rock shear strength, MPa; σ.sub.ucd is the dynamic rock uniaxial compressive strength, MPa; σ.sub.td is the dynamic rock tensile strength, MPa; σ.sub.sd is the dynamic rock shear strength, MPa.

10. The drill bit design method based on rock crushing principle with local variable strength according to claim 1, wherein the drill bit tooth parameters are an inclination angle and a spatial position of the drill bit tooth; in the Step S4, the adjusting the difference among the strength mode factors of the local crushing feature region comprises: when the local crushing feature region is the compressive crushing region:
ΔLSC≤20% when the local crushing feature region is the shear crushing region:
ΔLSS≤20% when the local crushing feature region is the tensile crushing region:
ΔLST≤20% when the local crushing feature region is the compressive-shear crushing region:
ΔLSCS≤25% when the local crushing feature region is the shear-tensile crushing region:
ΔLSST≤25% when the local crushing feature region is the compressive-tensile crushing region:
ΔLSCT≤25% wherein ΔLSC is the difference among the strength mode factors when the local crushing feature region is the compressive crushing region, dimensionless; ΔLSS is the difference among the strength mode factors when the local crushing feature region is the shear crushing region, dimensionless; ΔLST is the difference among the strength mode factors when the local crushing feature region is the tensile crushing region, dimensionless; ΔLSCS is the difference among the strength mode factors when the local crushing feature region is the compressive-shear crushing region, dimensionless; ΔLSST is the difference among the strength mode factors when the local crushing feature region is the shear-tensile crushing region, dimensionless; ΔLSCT is the difference among the strength mode factors when the local crushing feature region is the compressive-tensile crushing region, dimensionless.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Upon reading the following detailed description of preferred embodiments, various advantages and benefits will be apparent to those of ordinary skill in the art. The drawings are for the purpose of explaining preferred embodiments only, and do not constitute improper limitations on the present invention. The same components are also denoted by the same reference numerals throughout the drawings. In the drawings:

[0047] FIG. 1 is a flow chart of a drill bit design method based on rock crushing principle with local variable strength according to an embodiment of the application.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] The invention will be further described below in conjunction with the accompanying drawings, and the protection scope of the invention is not limited to the following.

Embodiment 1

[0049] As shown in FIG. 1, a drill bit design method based on rock crushing principle with local variable strength includes the following steps:

[0050] Step S1: a type of a drill bit, a number of blades and a type of a drill bit tooth are selected, and the drill bit is divided into a local crushing feature region as a whole according to a drill bit local crushing feature region division method by a processor, wherein the local crushing feature region includes a single crushing region and a mixed crushing region.

[0051] In the Step S1, the type of the drill bit includes a PDC drill bit and a PDC-roller-cone compact drill bit; the number of blades includes a PDC drill bit with 4 blades, a PDC drill bit with 5 blades, a PDC drill bit with 6 blades, a PDC-roller-cone compact drill bit with 4 blades and a PDC-roller-cone compact drill bit with 6 blades, wherein the PDC-roller-cone compact drill bit with 4 blades is a roller-cone with 2 blades plus PDC with 2 blades, and the PDC-roller-cone compact drill bit with 6 blades includes a roller-cone with 2 blades plus PDC with 4 blades and a roller-cone with 3 blades plus PDC with 3 blades; the type of drill bit tooth includes a plane cutting tooth and a tapered cutting tooth.

[0052] In the Step S1, the drill bit tooth local crushing feature region division method specifically includes the following steps:

[0053] symmetrical blades of the PDC drill bit with an even number of blades are classified into one group, and the drill bit tooth of the same type in each group of blades are divided into the local crushing feature region; the drill bit tooth of the same type of the PDC drill bit with an odd number of blades are divided into the local crushing feature region; PDC blades of the PDC-roller-cone compact drill bit are classified into the same group, the roller-cone blades are divided into the same group, and the drill bit tooth of the same type in each group are divided into the local crushing feature region.

[0054] In the Step S1, the single crushing region includes a compressive crushing region, a shear crushing region and a tensile crushing region; the mixed crushing region is divided into a compressive-shear crushing region, a shear-tensile crushing region and a compressive-tensile crushing region.

[0055] Step S2: a relationship among a dynamic rock uniaxial compressive strength, a static rock uniaxial compressive strength and a dynamic loading strain rate of a load is established by the processor; a relationship among a dynamic rock tensile strength, a static rock tensile strength and the dynamic loading strain rate of the load is established by the processor; a relationship among a dynamic rock shear strength, a static rock shear strength and the dynamic loading strain rate of the load is established by the processor.

[0056] In the Step S2, the method of using the processor for establishing the relationship among the dynamic rock uniaxial compressive strength, the static rock uniaxial compressive strength and the dynamic loading strain rate of the load specifically includes the following steps: the dynamic rock uniaxial compressive strength is measured by a split Hopkinson pressure bar (HSPB) rock mechanics experiment machine, and a curve fit is performed on a ratio between the dynamic rock uniaxial compressive strength and the static rock uniaxial compressive strength and the dynamic loading strain rate of the load, so as to finally establish a relationship among the dynamic rock uniaxial compressive strength, the static rock uniaxial compressive strength and the dynamic loading strain rate of the load by the processor, which is specifically expressed as follows:

[00016]$\frac{{\sigma }_{\mathrm{ucd}}}{{\sigma }_{\mathrm{uc}}}=\{\begin{array}{c}{a}_1{\stackrel{.}{\epsilon }}^{1/\left(1+n_c\right)}\left(\stackrel{.}{\epsilon }<{\stackrel{.}{\epsilon }}^{*}\right)\\ a_2{\stackrel{.}{\epsilon }}^{1/n}\left(\stackrel{.}{\epsilon }\ge {\stackrel{.}{\epsilon }}^{*}\right)\end{array}$

[0057] In the Step S2, the method of using the processor for establishing the relationship among the dynamic rock tensile strength, the static rock tensile strength and the dynamic loading strain rate of the load specifically includes the following steps: the dynamic rock tensile strength is measured by the SHPB rock mechanics experiment machine, and a curve fit is performed on a ratio between the dynamic rock tensile strength and the static rock tensile strength and the dynamic loading strain rate of the load, so as to finally establish a relationship among the dynamic rock tensile strength, the static rock tensile strength and the dynamic loading strain rate of the load by the processor, which is specifically expressed as follows:

[00017]$\frac{{\sigma }_{\mathrm{td}}}{{\sigma }_t}=\{\begin{array}{c}{b}_1{\stackrel{.}{\epsilon }}^{1/\left(1+n_c\right)}\left(\stackrel{.}{\epsilon }<{\stackrel{.}{\epsilon }}^{*}\right)\\ b_2{\stackrel{.}{\epsilon }}^{1/n}\left(\stackrel{.}{\epsilon }\ge {\stackrel{.}{\epsilon }}^{*}\right)\end{array}$

[0058] In the Step S2, the method of using the processor for establishing the relationship among the dynamic rock shear strength, the static rock shear strength and the dynamic loading strain rate of the load specifically includes the following steps: the dynamic rock shear strength is measured by the SHPB rock mechanics experiment machine, and a curve fit is performed on a ratio between the dynamic rock shear strength and the static rock shear strength and the dynamic loading strain rate of the load, so as to finally establish a relationship among the dynamic rock shear strength, the static rock shear strength and the dynamic loading strain rate of the load by the processor, which is specifically expressed as follows:

[00018]$\frac{{\sigma }_{\mathrm{sd}}}{{\sigma }_s}=\{\begin{array}{c}{c}_1{\stackrel{.}{\epsilon }}^{1/\left(1+n_c\right)}\left(\stackrel{.}{\epsilon }<{\stackrel{.}{\epsilon }}^{*}\right)\\ c_2{\stackrel{.}{\epsilon }}^{1/n}\left(\stackrel{.}{\epsilon }\ge {\stackrel{.}{\epsilon }}^{*}\right)\end{array}$

[0059] wherein a.sub.1, a.sub.2, b.sub.1, b.sub.2, c.sub.1, c.sub.2, n, n.sub.c are fit coefficients, dimensionless; σ.sub.uc is the static rock uniaxial compressive strength, MPa; σ.sub.t is the static rock tensile strength, MPa; σ.sub.s is the static rock shear strength, MPa; σ.sub.ucd is the dynamic rock uniaxial compressive strength, MPa; σ.sub.td is the dynamic rock tensile strength, MPa; σ.sub.sd is the dynamic rock shear strength, MPa; {dot over (ε)} is the dynamic loading strain rate of the load, s.sup.−1; {dot over (ε)}* is the dynamic loading critical strain rate of the load, s.sup.−1.

[0060] A calculation method of the dynamic loading strain rate of the load {dot over (ε)} in the process of crushing rocks with the drill bit tooth is expressed as follows:

[00019]$\stackrel{.}{\epsilon }=\frac{1.4v_c\sin \gamma }{d\sin \left(\gamma +\omega \right)}$

[0061] wherein {dot over (ε)} is the dynamic loading strain rate of the load, s.sup.−1; v.sub.c is the cutting tooth speed, mm/s; d is the cutting depth, mm; γ is the drill bit tooth caster angle, rad; ω is the scrap forming-compaction transition angle, rad.

[0062] The cutting speed v.sub.ci of the ith main cutting tooth on the drill bit is expressed as follows:

[00020]$v_{\mathrm{ci}}=\frac{\pi r_i{\mathrm{RPM}}_n}{30}$

[0063] wherein r.sub.i is a distance from a position where the ith main cutting tooth on the drill bit is located to an axis of the drill bit, m; RPM.sub.n is the rotating speed of the cutting tooth on the drill bit, r/min; v.sub.ci is the cutting speed of the ith cutting tooth on the drill bit, m/s.

[0064] Step S3: tooth distribution parameters are determined preliminarily according to drill bit tooth overall mechanics balance conditions by the processor, and bottom hole rock strength variation factors of the local crushing feature region and strength mode factors of the local crushing feature region are calculated according to the tooth distribution parameters of the drill bit and the relationship among the dynamic rock uniaxial compressive strength, the static rock uniaxial compressive strength and a dynamic loading strain rate of the load, the relationship among the dynamic rock tensile strength, the static rock tensile strength and the dynamic loading strain rate of the load and the relationship among the dynamic rock shear strength, the static rock shear strength and the dynamic loading strain rate of the load established in the Step S2.

[0065] In the Step S3, the tooth distribution parameters include the number of drill bit tooth, a diameter of each of the drill bit tooth, a caster angle of each of the drill bit tooth, and a distance from a position where each of the main cutting tooth is located to the axis of the drill bit.

[0066] In the Step S3, the method of calculating bottom hole rock strength variation factors of the local crushing feature region specifically includes the following steps: a relationship between the bottom hole rock strength variation factors and the drill bit tooth distribution parameters corresponding to each of the main cutting tooth is obtained by the curve fit method according to the relationship among the dynamic rock uniaxial compressive strength, the static rock uniaxial compressive strength and the dynamic loading strain rate of the load, the relationship among the dynamic rock tensile strength, the static rock tensile strength and the dynamic loading strain rate of the load and the relationship among the dynamic rock shear strength, the static rock shear strength and the dynamic loading strain rate of the load obtained in the Step S2, which is specifically expressed as follows:

[00021]$\begin{array}{c}\frac{{\sigma }_{\mathrm{ucdi}}}{{\sigma }_{\mathrm{uc}}}=\{\begin{array}{c}{a}_{1i}{v}_{\mathrm{ci}}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/\left(1+n_{\mathrm{ci}}\right)}\left(\stackrel{.}{\epsilon }<{\stackrel{.}{\epsilon }}^{*}\right)\\ a_{2i}{v}_{\mathrm{ci}}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/n_i}\left(\stackrel{.}{\epsilon }\ge {\stackrel{.}{\epsilon }}^{*}\right)\end{array}\\ \frac{{\sigma }_{\mathrm{sdi}}}{{\sigma }_s}=\{\begin{array}{c}{b}_{1i}{v}_{\mathrm{ci}}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/\left(1+n_{\mathrm{ci}}\right)}\left(\stackrel{.}{\epsilon }<{\stackrel{.}{\epsilon }}^{*}\right)\\ b_{2i}{v}_{\mathrm{ci}}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/n_i}\left(\stackrel{.}{\epsilon }\ge {\stackrel{.}{\epsilon }}^{*}\right)\end{array}\\ \frac{{\sigma }_{\mathrm{tdi}}}{{\sigma }_t}=\{\begin{array}{c}{c}_{1i}{v}_{\mathrm{ci}}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/\left(1+n_{\mathrm{ci}}\right)}\left(\stackrel{.}{\epsilon }<{\stackrel{.}{\epsilon }}^{*}\right)\\ c_{2i}{v}_{\mathrm{ci}}.Math.{\frac{1.4\sin \gamma }{d\sin \left(\gamma +\omega \right)}}^{1/n_i}\left(\stackrel{.}{\epsilon }\ge {\stackrel{.}{\epsilon }}^{*}\right)\end{array}\end{array}$

[0067] wherein a.sub.1i, a.sub.2i, b.sub.1i, b.sub.2i, c.sub.1i, c.sub.2i, n.sub.i, n.sub.ci are fit coefficients of the strength variation factor expression corresponding to the ith cutting tooth on the drill bit, dimensionless; σ.sub.ucdi is the dynamic uniaxial compressive strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, MPa;

[00022]$\frac{{\sigma }_{\mathrm{ucdi}}}{{\sigma }_{\mathrm{uc}}}$

is the ratio between the dynamic uniaxial compressive strength and the static uniaxial compressive strength in the process of dynamically crushing rocks of the i th cutting tooth on the drill bit, compressive strength variation factors for short, dimensionless; σ.sub.sdi is the dynamic shear strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, MPa;

[00023]$\frac{{\sigma }_{\mathrm{sdi}}}{{\sigma }_s}$

is the ratio between the dynamic shear strength and the static shear strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, shear strength variation factors for short, dimensionless; σ.sub.tdi is the dynamic tensile strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, MPa;

[00024]$\frac{{\sigma }_{\mathrm{tdi}}}{{\sigma }_t}$

is the ratio between the dynamic tensile strength and the static tensile strength in the process of dynamically crushing rocks of the ith cutting tooth on the drill bit, tensile strength variation factors for short, dimensionless; σ.sub.uc is the static rock uniaxial compressive strength, MPa; σ.sub.t is the static rock tensile strength, MPa; σ.sub.s is the static rock shear strength, MPa; v.sub.ci is the cutting speed of the ith cutting tooth on the drill bit, m/s; d is the cutting depth, mm; γ is the caster angle of the drill bit tooth, rad; ω is the scrap forming-compaction transition angle, rad; {dot over (ε)}* is the dynamic loading critical strain rate of the load, s.sup.−1.

[0068] In the Step S3, a method of calculating the strength mode factors of the local crushing feature region includes the following steps:

[0069] when the local crushing feature region is the compressive crushing region:

[00025]$\mathrm{LSC}=\mathrm{Max}\left\{\frac{{\sigma }_{\mathrm{ucd}1}}{{\sigma }_{\mathrm{uc}}},\frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{\mathrm{uc}}},\frac{{\sigma }_{\mathrm{ucd}3}}{{\sigma }_{\mathrm{uc}}}.Math.\frac{{\sigma }_{\mathrm{ucdk}}}{{\sigma }_{\mathrm{uc}}}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{\mathrm{ucd}1}}{{\sigma }_{\mathrm{uc}}},\frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{\mathrm{uc}}},\frac{{\sigma }_{\mathrm{ucd}3}}{{\sigma }_{\mathrm{uc}}}.Math.\frac{{\sigma }_{\mathrm{ucdk}}}{{\sigma }_{\mathrm{uc}}}\right\}$

[0070] when the local crushing feature region is the shear crushing region:

[00026]$\mathrm{LSS}=\mathrm{Max}\left\{\frac{{\sigma }_{\mathrm{sd}1}}{{\sigma }_s},\frac{{\sigma }_{\mathrm{sd}2}}{{\sigma }_s},\frac{{\sigma }_{\mathrm{sd}3}}{{\sigma }_s}.Math.\frac{{\sigma }_{\mathrm{sdl}}}{{\sigma }_s}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{\mathrm{sd}1}}{{\sigma }_s},\frac{{\sigma }_{\mathrm{sd}2}}{{\sigma }_s},\frac{{\sigma }_{\mathrm{sd}3}}{{\sigma }_s}.Math.\frac{{\sigma }_{\mathrm{sdl}}}{{\sigma }_s}\right\}$

[0071] when the local crushing feature region is the tensile crushing region:

[00027]$\mathrm{LST}=\mathrm{Max}\left\{\frac{{\sigma }_{\mathrm{td}1}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{td}2}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{td}3}}{{\sigma }_t}.Math.\frac{{\sigma }_{\mathrm{tdn}}}{{\sigma }_t}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{\mathrm{td}1}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{td}2}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{td}3}}{{\sigma }_t}.Math.\frac{{\sigma }_{\mathrm{tdn}}}{{\sigma }_t}\right\}$

[0072] when the local crushing feature region is the compressive-shear crushing region:

[00028]$\mathrm{LSCS}=\mathrm{Max}\left\{\frac{{\sigma }_{\mathrm{ucd}1}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{sd}1}}{{\sigma }_s},\frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{sd}2}}{{\sigma }_s},\frac{{\sigma }_{\mathrm{ucd}3}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{sd}3}}{{\sigma }_s},.Math.\frac{{\sigma }_{\mathrm{ucdk}}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{sdm}}}{{\sigma }_s}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{\mathrm{ucd}1}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{sd}1}}{{\sigma }_s},\frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{sd}2}}{{\sigma }_s},\frac{{\sigma }_{\mathrm{ucd}3}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{sd}3}}{{\sigma }_s},.Math.\frac{{\sigma }_{\mathrm{ucdk}}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{sdm}}}{{\sigma }_s}\right\}$

[0073] when the local crushing feature region is the shear-tensile crushing region:

[00029]$\mathrm{LSST}=\mathrm{Max}\left\{\frac{{\sigma }_{\mathrm{sd}1}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{td}1}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{sd}2}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{td}2}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{sd}3}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{td}3}}{{\sigma }_t},.Math.\frac{{\sigma }_{\mathrm{sdj}}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{tdj}}}{{\sigma }_t}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{\mathrm{sd}1}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{td}1}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{sd}2}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{td}2}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{sd}3}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{td}3}}{{\sigma }_t},.Math.\frac{{\sigma }_{\mathrm{sdj}}}{{\sigma }_s}-\frac{{\sigma }_{\mathrm{tdj}}}{{\sigma }_t}\right\}$

[0074] when the local crushing feature region is the compressive-tensile crushing region:

[00030]$\mathrm{LSCT}=\mathrm{Max}\left\{\frac{{\sigma }_{\mathrm{ucd}1}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{td}1}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{td}2}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{ucd}3}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{td}3}}{{\sigma }_t},.Math.\frac{{\sigma }_{\mathrm{ucdq}}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{tdq}}}{{\sigma }_t}\right\}-\mathrm{Min}\left\{\frac{{\sigma }_{\mathrm{ucd}1}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{td}1}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{ucd}2}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{td}2}}{{\sigma }_t},\frac{{\sigma }_{\mathrm{ucd}3}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{td}3}}{{\sigma }_t},.Math.\frac{{\sigma }_{\mathrm{ucdq}}}{{\sigma }_{\mathrm{uc}}}-\frac{{\sigma }_{\mathrm{tdq}}}{{\sigma }_t}\right\}$

[0075] wherein LSC is the strength mode factor when the local crushing feature region is the compressive crushing region, dimensionless; LSS is the strength mode factor when the local crushing feature region is the shear crushing region, dimensionless; LST is the strength mode factor when the local crushing feature region is the tensile crushing region, dimensionless; LSCS is the strength mode factor when the local crushing feature region is the compressive-shear crushing region, dimensionless; LSST is the strength mode factor when the local crushing feature region is the shear-tensile crushing region, dimensionless; LSCT is the strength mode factor when the local crushing feature region is the compressive-tensile crushing region, dimensionless; k is the number of the cutting tooth when the local crushing feature region is the compressive crushing region, dimensionless; l is the number of the cutting tooth when the local crushing feature region is the shear crushing region, dimensionless; n is the number of the cutting tooth when the local crushing feature region is the tensile crushing region, dimensionless; m is the number of the cutting tooth when the local crushing feature region is the compressive-shear crushing region, dimensionless; j is the number of the cutting tooth when the local crushing feature region is the shear-tensile crushing region, dimensionless; q is the number of the cutting tooth when the local crushing feature region is the compressive-tensile crushing region, dimensionless; σ.sub.uc is the static rock uniaxial compressive strength, MPa; σ.sub.t is the static rock tensile strength, MPa; σ.sub.s is the static rock shear strength, MPa; σ.sub.ucd is the dynamic rock uniaxial compressive strength, MPa; σ.sub.td is the dynamic rock tensile strength, MPa; σ.sub.sd is the dynamic rock shear strength, MPa.

[0076] Step S4: a difference among the strength mode factors of the single crushing region is controlled within 20% and a difference among the strength mode factors of the mixed crushing region is controlled within 25% by adjusting drill bit parameters and regulating a difference among the strength mode factors of the local crushing feature region by the processor in the Step S3.

[0077] The drill bit tooth parameters are an inclination angle and a spatial position of the drill bit tooth; in the Step S4, the adjusting the difference among the strength mode factors of the local crushing feature region includes the following steps:

[0078] when the local crushing feature region is the compressive crushing region:

ΔLSC≤20%

[0079] when the local crushing feature region is the shear crushing region:

ΔLSS≤20%

[0080] when the local crushing feature region is the tensile crushing region:

ΔLST≤20%

[0081] when the local crushing feature region is the compressive-shear crushing region:

ΔLSCS≤25%

[0082] when the local crushing feature region is the shear-tensile crushing region:

ΔLSST≤25%

[0083] when the local crushing feature region is the compressive-tensile crushing region:

ΔLSCT≤25%

[0084] wherein ΔLSC is the difference among the strength mode factors when the local crushing feature region is the compressive crushing region, dimensionless; ΔLSS is the difference among the strength mode factors when the local crushing feature region is the shear crushing region, dimensionless; ΔLST is the difference among the strength mode factors when the local crushing feature region is the tensile crushing region, dimensionless; ΔLSCS is the difference among the strength mode factors when the local crushing feature region is the compressive-shear crushing region, dimensionless; ΔLSST is the difference among the strength mode factors when the local crushing feature region is the shear-tensile crushing region, dimensionless; ΔLSCT is the difference among the strength mode factors when the local crushing feature region is the compressive-tensile crushing region, dimensionless.

[0085] Step S5: the difference among the strength mode factors of the local crushing feature region obtained in the Step S4 is treated as a target control condition for drill bit design by the processor, wherein the drill bit design is completed if the target control condition for drill bit design is met, and the drill bit tooth distribution parameters are continued to be adjusted to meet the target control condition for drill bit design to complete the drill bit design if the target control condition for drill bit design is not met.

[0086] The invention discloses a drill bit design method based on rock crushing principle with local variable strength. The method includes: first, the drill bit is divided into local crushing feature regions as a whole; then, strength mode factors of the local crushing feature regions are calculated; and then, a different among the strength mode factors of the local crushing feature regions is obtained to obtain a vector sum of horizontal cutting forces of the drill bit tooth corresponding to the same group of cutting tooth on the drill bit; finally, treating the difference among the strength mode factors of the local crushing feature region as a target control condition for drill bit design. In this method, based on the rock crushing principle with local variable strength, after dividing the symmetrical cutting tooth into groups, the strength variation factors of the symmetrical position are adjusted and balanced, and the strength of different symmetrical positions on the drill bit can be adjusted to be different, so that the rock crushing strength of different local crushing feature regions can be changed in a targeted manner, and the failure of the drill bit caused by the inability to control the strength of each main cutting tooth of the traditional drill bit by region is eliminated, thereby improving the rock crushing efficiency of the drill bit, prolonging the service time and having broad application prospects.

[0087] So far, those skilled in the art realize that although embodiments of the invention have been shown and described in detail herein, numerous other variations or modifications consistent with the principles of the invention may be directly determined or derived from the disclosure without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and deemed to cover all such other variations or modifications.