Method and apparatus for the measurement of the electrical resistivity of geologic formations employing modeling data
First Claim
1. A method for measuring characteristics of a geologic formation, said method comprising:
- producing, within a first area or said geologic formation, a first magnetic field;
sensing, within a second area of said geologic formation, a second magnetic field, with said second area being spaced-apart from said first area, with said first and second magnetic field being produced with one of said first and second areas being surrounded with an electrically conductive liner, said liner having an attenuation factor associated therewith;
forming a signal corresponding to said second magnetic field, said signal including information corresponding to said attenuation factor;
calculating a modeled magnetic field corresponding to said second magnetic field in an absence of said electrically conductive liner, defining a modeled representation;
obtaining a quantitative value of said attenuation factor by dividing said signal by said modeled representation, removing said information from said signal by dividing said signal with said quantitative value, defining a corrected signal; and
measuring said characteristics as a function of said corrected signal.
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Abstract
Provided are a method, a computer program product and a system, to measure characteristics of a geologic formation, such as hydrocarbon reservoirs, that employs modeling data to remove unwanted information from a signal carrying information concerning the geologic formation. This allows obtaining accurate information concerning the resistivity of geologic formations in which a borehole has been formed and encased with a conductive liner, such as a steel casing. Specifically, it was recognized that a magnetic field produced within a borehole that has been cased is substantially similar to magnetic field produced from a borehole that was not cased, i.e., the spatial distribution and orientation to the two aforementioned magnetic fields are the same, differing only by a constant related to the casing attenuation factor. The magnetic field outside of the cased borehole is reduced in amplitude by an attenuation factor associated with the liner. Thus, the magnetic field produced at a point outside of the liner is a function of the product of term for the attenuation factor of the liner, ke and a term for the response of the geologic formation, ƒ. Both terms are independent of the other. Thus, by factoring and removing information concerning the attenuation factor, ke, accurate measurements of the geologic formation may be determined.
103 Citations
24 Claims
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1. A method for measuring characteristics of a geologic formation, said method comprising:
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producing, within a first area or said geologic formation, a first magnetic field;
sensing, within a second area of said geologic formation, a second magnetic field, with said second area being spaced-apart from said first area, with said first and second magnetic field being produced with one of said first and second areas being surrounded with an electrically conductive liner, said liner having an attenuation factor associated therewith;
forming a signal corresponding to said second magnetic field, said signal including information corresponding to said attenuation factor;
calculating a modeled magnetic field corresponding to said second magnetic field in an absence of said electrically conductive liner, defining a modeled representation;
obtaining a quantitative value of said attenuation factor by dividing said signal by said modeled representation, removing said information from said signal by dividing said signal with said quantitative value, defining a corrected signal; and
measuring said characteristics as a function of said corrected signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A computer program product for measuring characteristics of a geologic formation, said method comprising:
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code to produce, within a first area of said geologic formation, a first magnetic field;
code to sense, within a second area of said geologic formation, a second magnetic field, with said second area being spaced-apart from said first area, with one of said first and second areas being surrounded with all electrically conductive liner, said liner having an attenuation factor associated therewith;
code to form a signal corresponding to said second magnetic field, with said signal including information corresponding to said attenuation factor;
code to calculate a modeled magnetic field corresponding to said second magnetic field in an absence of said electrically conductive liner, defining a modeled representation;
code to obtain a quantitative value of said attenuation factor by dividing said signal by said modeled representation;
code to remove said information from said signal by dividing said signal with said quantitative value, defining a corrected signal; and
code to measure said characteristics as a function of said corrected signal. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 20)
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19. A system for measuring characteristics of a geologic formation disposed between first and second spaced-apart areas, one of which surrounded with an electrically conductive liner, said system comprising:
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a transmitting unit disposed within said first area;
a signal generator in data communication with said transmitting unit;
a receiving unit disposed in said second area;
a processor in data communication with both said transmitting unit and said receiving unit; and
a memory in data communication with said processor, said memory including code to produce, within a first area of said geologic formation, a first magnetic field;
code to sense, within a second area of said geologic formation, a second magnetic field;
code to form a signal corresponding to said second magnetic field, with said signal including information corresponding to said attenuation factor;
code to calculate a modeled magnetic field corresponding to said second magnetic field in an absence of said electrically conductive liner, defining a modeled representation;
code to obtain a quantitative value of said attenuation factor by dividing said signal by said modeled representation;
code to remove said information from said signal by dividing said signal with said quantitative value, defining a corrected signal; and
code to measure said characteristics as a function of said corrected signals.- View Dependent Claims (21, 22, 23, 24)
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Specification