EP0466255A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Method of determining the drilling conditions associated with the drilling of a formation with a drag bit
Assignee: Services Petroliers Schlumberger SA
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Filing: 1991-07-03
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Granted: —
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Expires: 2011-07-03
Abstract
Abstract This invention is based on a new model describing the drilling process of a drag bit and concerns a method of determining the drilling conditions associated with the drilling of a borehole through subterranean formations, each one corresponding to a particular lithology, the borehole being drilled with a rotary drag bit, the method comprising the steps of: measuring the weight W applied on the bit, the bit torque T, the angular rotation speed ω of the bit and the rate of penetration v of the bit to obtain sets of data (W i , T i , v i , ω i ) corresponding to different depths; calculating the specific energy E i and the drilling strength S from the data (W i , T i , v i , ω i ); identifying at least one linear cluster of values (E i , S i ), said cluster corresponding to a particular lithology; and determining the drilling conditions from said linear cluster. The slope of the linear cluster is determined, from which the internal friction angle φ of the formation is estimated. The intrinsic specific energy ∈ of the formation and the drilling efficiency are also determined. Change of lithology, wear of the bit and bit balling can be detected.
Inventors
- 👤 Emmanuel Detournay
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 21:43
CPC Classifications
E; E21; E21B; E21B49/00; E21B49/003; E21B12/00; E21B12/02; E21B44/00
Claims Analysis
Total Claims: 32
Claim 1
Independent Claim
152 words
A method of determining the drilling conditions associated with the drilling of a borehole through subterranean formations, each one corresponding to a particular lithology, the borehole being drilled with a rotary drag bit, wherein the weight W applied on the bit, the bit torque T, the angular rotation speed ω of the bit and the rate of penetration v of the bit are measured to obtain sets of data (W ; , T i , v i , ω i ) corresponding to different depths, the method being characterised by the following steps: - calculating the specific energy E i and the drilling strength S from the data (W ; , T i , v i , ω i ); - identifying at least one linear cluster of values (E i , S i ), said cluster corresponding to a particular lithology; and - determining the drilling conditions from said linear cluster.
Claim 2
Independent Claim
152 words
A method of determining the drilling conditions associated with the drilling of a borehole through subterranean formations, each one corresponding to a particular lithology, the borehole being drilled with a rotary drag bit, wherein the weight W applied on the bit, the bit torque T, the angular rotation speed ω of the bit and the rate of penetration v of the bit are measured to obtain sets of data (W ; , T i , v i , ω i ) corresponding to different depths, the method being characterised by the following steps: - calculating the specific energy E i and the drilling strength S from the data (W ; , T i , v i , ω i ); - identifying at least one linear cluster of values (E i , S i ), said cluster corresponding to a particular lithology; and - determining the drilling conditions from said linear cluster.
Claim 3
Dependent Claim
53 words
The method of claim 1, further comprising the step of determining the slope of said linear cluster, said slope being defined as the ratio of the variation of E over the corresponding variation of S and said slope being related to the product of a bit constant γ by a friction coefficient µ..
Claim 4
Dependent Claim
30 words
The method of claim 2, further comprising the step of computing the value of said friction coefficient µ. from said slope and from a known or estimated value of γ.
Claim 5
Dependent Claim
30 words
The method of claim 3, further comprising the step of deriving an indication of the internal friction angle φ of the formation from the value of said friction coefficient µ.
Claim 6
Dependent Claim
45 words
The method of claim 2, further comprising the steps of estimating the intrinsic specific energy ∈ by the following relationship: wherein E o is the intercept of the extension of said linear cluster with the E-axis, µ γ is said slope and is a constant.
Claim 7
Dependent Claim
44 words
The method of claim 5, further comprising the step of estimating the amount of E f of the drilling energy spent in frictional process at a certain depth by comparing the value E i at said depth with said intrinsic specific energy E .
Claim 8
Independent Claim
48 words
The method of any of the preceding claims, further comprising the step of determining the efficiency η of the drilling process at a particular depth by finding out in the linear cluster the position of the pair (E i , S i ) corresponding to said particular depth.
Claim 9
Dependent Claim
37 words
The method of claim 7, wherein the highest efficiency achieved when drilling said particular lithology is determined by identifying the minimum value of E i and S i , said minimum value corresponding to said highest efficiency.
Claim 10
Dependent Claim
22 words
The method of claim 7, further comprising the step of estimating the intrinsic specific energy ∈ from the minimum value of E.
Claim 11
Dependent Claim
44 words
The method of claim 9, further comprising the step of estimating the amount E f of the drilling energy spent in a frictional process at a certain depth by comparing the value E i at said depth with said intrinsic specific energy E .
Claim 12
Independent Claim
35 words
The method of any of the preceding claims, further comprising the step of estimating the efficiency of the drilling process at a certain depth by computing the ratio E i /S i at said depth.
Claim 13
Independent Claim
107 words
The method of one of the claims 7 and 11, further comprising the step of estimating the values (E;, S i ) M associated with the cutting point which corresponds to an efficiency equal substantially to 1 and determining the locus of all the cutting points whose coordinates (E i , S i ) correspond to a drilling efficiency substantially equal to 1 when there is a change in the pore pressure of the formation and/or in the drilling fluid pressure, said locus being determined by a linear relationship including the pair (E = 0, S = 0) and said pair (E;, S i ) M .
Claim 14
Independent Claim
71 words
The method of any of the preceding claims, further comprising the step of estimating the state of wear of the drillbit by following the evolution of the values E and S while drilling, a sharp drillbit being characterised by relatively small values of E and S and these values increasing with the wear of the drillbit resulting in a stretch of said linear cluster towards higher values of E and S.
Claim 15
Independent Claim
46 words
The method of one of the claims 7 and 11, further comprising the step of detecting a bit balling event by comparing the successive values of the drilling efficiency computed as the drilling progresses in a soft formation and identifying small values of the drilling efficiency.
Claim 16
Independent Claim
43 words
The method of claims 3 and 14, wherein the step of detecting a bit balling event further comprises the determination of the value of the friction coefficient µ, and declaring a bit balling event if said value of µ is less than 0.5.
Claim 17
Independent Claim
48 words
The method of any of the preceding claims, further comprising the detection of a change of lithology by identifying the beginning of another linear cluster having a different slope from the slope of said one linear cluster, the drilling fluid pressure p h having been kept relatively constant.
Claim 18
Independent Claim
40 words
The method of any of the preceding claims, wherein at least part of the data (W i , T i , v i , ω i ) are average values of W, T, v and ω over predetermined depth intervals.
Claim 19
Independent Claim
46 words
The method of any of the preceding claims, wherein the drilling specific energy E and the drilling strength S are respectively computed from the following equations: wherein a is the radius of the bit and 6 is the depth of cut per bit revolution calculated as:
Claim 20
Independent Claim
37 words
The method of any of the preceding claims, wherein said linear cluster of values (E i , S i ) corresponds to the following equation: wherein γ is a bit constant and µ is a friction coefficient.
Claim 21
Dependent Claim
36 words
The method of claim 19, wherein ∈ being the intrinsic specific energy of the formation and being a quantity related to the friction at the interface between the cutting face of the cutter and the rock.
Claim 22
Dependent Claim
38 words
The method of claim 20, wherein 0 being the backrake angle of the drillbit cutters and being a quantity related to the friction angle ψ at the interface between the cutting face of the cutter and the rock.
Claim 23
Independent Claim
24 words
The method of any of the preceding claims, wherein the different values (E i , S i ) are represented in a diagram E-S.
Claim 24
Independent Claim
36 words
The method of any of the preceding claims, further comprising the step of varying at least one of the drilling parameters, weight-on-bit W and rotation speed ω, in order to define more precisely said linear cluster.
Claim 25
Independent Claim
124 words
A method of determining the efficiency of at least one drag drillbit wherein a substantially uniform rock of known properties is drilled with the drillbit and wherein the weight-on-bit W, the torque T, the bit rate of penetration v and the angular velocity of the bit ω are measured to obtain sets of data (W i , T i , v i , ω i )-,the method being characterised by the following steps: - calculating the specific energy E i and the drilling strength S i from the data (W i , T i , v i , ω i ); - identifying a linear cluster of values (E i , S i ); and - determining the drillbit efficiency from said linear cluster.
Claim 26
Independent Claim
124 words
A method of determining the efficiency of at least one drag drillbit wherein a substantially uniform rock of known properties is drilled with the drillbit and wherein the weight-on-bit W, the torque T, the bit rate of penetration v and the angular velocity of the bit ω are measured to obtain sets of data (W i , T i , v i , ω i )-,the method being characterised by the following steps: - calculating the specific energy E i and the drilling strength S i from the data (W i , T i , v i , ω i ); - identifying a linear cluster of values (E i , S i ); and - determining the drillbit efficiency from said linear cluster.
Claim 27
Dependent Claim
25 words
The method of claim 24, further comprising the step of determining the slope of said linear cluster and determining the drillbit efficiency from said slope.
Claim 28
Dependent Claim
32 words
The method of claim 25, wherein the efficiency of at least two drag drillbits are determined and compared; the drillbit of higher efficiency being identified with the linear cluster of lower slope.
Claim 29
Independent Claim
47 words
The method of any of the claims 24 to 26, wherein the drilling specific energy ∈ and the drilling strength are respectively computed from the following equations: wherein a is the radius of the bit and 6 is the depth of cut per bit revolution calculated as:
Claim 30
Independent Claim
52 words
The method of any of the preceding claims 24 to 27, wherein said linear cluster of values (E i , S i ) corresponds to the following equation: wherein µ is a constant characteristic of the rock and γ is a bit constant from which the efficiency of the drillbit is determined.
Claim 31
Independent Claim
36 words
A method as claimed in any preceding claim wherein the difference between a pair of values (E i ,S i ) from the linear cluster of similar values is used to identify an event affecting drilling.
Claim 32
Independent Claim
38 words
A method as claimed in any preceding claim, wherein the contact length λ and the contact stress a are determined and the development of the contact force λσ is monitored to determine changes in bit wear and lithology.
References Cited (Backward Citations)
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