Downhole rebound hardness measurement while drilling or wireline logging
First Claim
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1. A method of estimating a rock strength profile of a formation, comprising:
- conveying a tool having a testing surface into a wellbore in the formation;
determining an orientation of the testing surface using an orientation sensor conveyed downhole;
propelling the testing surface along a selected direction corresponding to the determined orientation to impact the formation, wherein an energy of impact of the testing surface against the formation is affected by a component of gravitational force along the selected direction;
obtaining a measurement of hardness of the formation under in-situ stress conditions from a rebound of the testing surface from the formation;
selecting a hardness scale for the determined orientation of the testing surface;
measuring a rock density of the formation using a downhole sensor;
selecting a relationship between the selected rock hardness scale and rock strength for the measured rock density; and
determining a rock strength of the formation indicated by the measurement of hardness using the selected hardness scale and the relationship between the selected rock hardness scale and rock strength.
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Abstract
A method and apparatus for estimating a rock strength profile of a formation is disclosed. A tool having a testing surface is conveyed into a wellbore in the formation. The testing surface is propelled to impact the formation at a plurality of depths in the wellbore. A measurement of hardness of the formation is obtained from a rebound of the testing surface from the formation at the plurality of depths. The rock strength profile of the formation is estimated using the obtained measurements of hardness at the plurality of depths. A parameter for drilling the wellbore can be affected using the estimated rock strength profile.
26 Citations
17 Claims
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1. A method of estimating a rock strength profile of a formation, comprising:
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conveying a tool having a testing surface into a wellbore in the formation; determining an orientation of the testing surface using an orientation sensor conveyed downhole; propelling the testing surface along a selected direction corresponding to the determined orientation to impact the formation, wherein an energy of impact of the testing surface against the formation is affected by a component of gravitational force along the selected direction; obtaining a measurement of hardness of the formation under in-situ stress conditions from a rebound of the testing surface from the formation; selecting a hardness scale for the determined orientation of the testing surface; measuring a rock density of the formation using a downhole sensor; selecting a relationship between the selected rock hardness scale and rock strength for the measured rock density; and determining a rock strength of the formation indicated by the measurement of hardness using the selected hardness scale and the relationship between the selected rock hardness scale and rock strength. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of drilling a wellbore, comprising:
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conveying a tool having a testing surface, an orientation sensor and a rock density sensor into a wellbore in the formation; determining an orientation of the testing surface using the orientation sensor; propelling the testing surface in a selected direction corresponding to the determined orientation to impact the formation, wherein an energy of impact of the testing surface against the formation is affected by a component of gravitational force along the selected direction; determining the rock density of the formation using the rock density sensor; using a processor to; select a hardness scale for the determined orientation, measure a rock density of the formation using a downhole sensor, select a linear relationship between the selected rock hardness scale and rock strength for the measured rock density, and determine a rock strength of the formation indicated by the measurement of hardness using the selected hardness scale and the relationship between the selected rock hardness scale and rock strength, and affect a parameter for drilling the wellbore using the estimated rock strength.
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12. An apparatus for estimating a rock strength of a formation, comprising:
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a tool configured to be conveyed into the wellbore; a testing surface disposed on the tool configured to propel against the formation in a selected direction and rebound from the formation, wherein an energy of impact of the testing surface against the formation is affected by a component of gravitational force along the selected direction; and an orientation sensor disposed on the tool configured to determine an orientation of the tool in the wellbore; a rock density sensor disposed on the tool; a processor configured to; obtain a measurement of hardness of the formation under in-situ stress conditions from a rebound of the testing surface from the formation, obtain the orientation of the tool from the orientation sensor, obtain the rock density of the formation from the rock density sensor, select a hardness scale for the determined orientation, measure a rock density of the formation using a downhole sensor, select a linear relationship between the selected rock hardness scale and rock strength for the measured rock density, and determine a rock strength of the formation indicated by the measurement of hardness using the selected hardness scale and the relationship between the selected rock hardness scale and rock strength. - View Dependent Claims (13, 14, 15, 16, 17)
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Specification