Method of determining rock compressive strength
First Claim
1. A method of determining rock compressive strength of a subterranean formation penetrated by a wellbore comprising:
- (a) obtaining a numerical model of a drill bit to be used to drill through the subterranean formation;
(b) obtaining an estimate of the rock ductility of the subterranean formation;
(c) measuring weight-on-bit (WOB) and bit rotational speed (RPM) as the drill bit drills through the subterranean formation; and
(d) determining the rock compressive strength of the subterranean formation from the numerical model of the drill bit, the estimate of rock ductility, and weight-on-bit (WOB) and bit rotational speed (RPM).
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Abstract
A method is disclosed for determining rock compressive strength of a subterranean formation penetrated by a wellbore. A mathematical model of a drill bit and an estimate of rock ductility of a particular subterranean formation in conjunction with weight-on-bit (WOB), bit rotational speed RPM, and rate of penetration (ROP) are used as inputs. From the above inputs, the rock compressive strength can be determined while the wellbore is being drilled or afterwards. A depth correlated log can be generated of rock compressive strength that can be compared to other logs obtained from adjacent wellbores to obtain a refined estimate of the depth of a particular subterranean formation feature. Further, the above method can be utilized for obtaining an indication of bit wear or bit damage while the bit is drilling a wellbore by comparing a first rock compressive strength log of a wellbore to a rock compressive strength log being generated while the drill bit is actually drilling a second wellbore. Any significant deviation between the two logs provides an indication of bit wear or bit damage.
58 Citations
7 Claims
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1. A method of determining rock compressive strength of a subterranean formation penetrated by a wellbore comprising:
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(a) obtaining a numerical model of a drill bit to be used to drill through the subterranean formation; (b) obtaining an estimate of the rock ductility of the subterranean formation; (c) measuring weight-on-bit (WOB) and bit rotational speed (RPM) as the drill bit drills through the subterranean formation; and (d) determining the rock compressive strength of the subterranean formation from the numerical model of the drill bit, the estimate of rock ductility, and weight-on-bit (WOB) and bit rotational speed (RPM). - View Dependent Claims (2, 3, 4, 5)
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6. A method of generating a log of rock compressive strength comprising:
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(a) obtaining numerical models of drill bits to be utilized in drilling a wellbore through subterranean formations; (b) obtaining an estimate of rock ductility of the subterranean formations; (c) measuring weight-on-bit (WOB) and bit rotational speed (RPM) as the drill bits pass through the subterranean formations; (d) determining the rock compressive strength of the subterranean formations from the numerical models of the drill bits, the estimate of rock ductility, and weight-on-bit (WOB) and bit rotational speed (RPM); and (e) outputting a depth correlated log of rock compressive strength. - View Dependent Claims (7)
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Specification