Retrievable resistivity logging system for use in measurement while drilling
First Claim
1. A resistivity logging system for use in measurement while drilling operations wherein the logging system is located in a down-hole assembly near a drill bit while a well is being drilled, the logging system comprising:
- a drill collar having a selected length;
a transmitter sub connected to one end of the drill collar, the transmitter subhaving an insulating layer that electrically isolates a first portion of the transmitter sub from a second portion of the transmitter sub, wherein the first portion of the transmitter sub includes a first conductive material on a first inner annular surface of the first portion, and the second portion of the transmitter sub includes a second conductive material disposed on a second inner annular surface of the second portion;
a receiver sub connected to a second end of the drill collar, the receiver subincluding at least one receiver electrode disposed over a selected portion of an outer annular surface of the receiver sub and at least one receiver electrode contact disposed on a selected portion of an inner annular surface of the receiver sub, the at least one receiver electrode coupled to the at least one receiver electrode contact via a conductive material disposed in the receiver sub, the conductive material being surrounded with insulating material;
an instrument cartridge having a conductive body positionable within the drillcollar and subs, the cartridge including;
at least a first electrical contact forconductively coupling with the conductive material disposed on the first inner annular surface of the transmitter sub;
at least a second electrical contact for conductively coupling with the conductive material disposed on the second inner annular surface of the transmitter sub;
at least a third electrical contact for conductivelycoupling with the at least one receiver electrode contact;
at least a fourth electrical contact for conductivelycoupling with a portion of the inner annular surface of the receiver sub that is independent of the conductive material and the insulating material; and
current injection circuitry connected to inject current into the formationthrough the first electrical contact and current sensing circuitry connected to sense the current returned through the third electrical contact.
1 Assignment
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Accused Products
Abstract
A retrievable resistivity logging system is provided for obtaining directional resistivity information while drilling (e.g., in an MWD system). The information obtained by this system can be used to determine the proximity of resistivity discontinuities and for use in steering the progress of the wellbore in the presence of geological boundaries of interest. In preferred embodiments, the logging system comprises passive transmitter and receiver electrodes built into subs that are incorporated into the drillstring, and a retrievable instrument cartridge that comprises spring loaded contacts that engage contact surfaces in the subs to connect the electrodes to the cartridge. In some embodiments, the cartridge comprises toroidal transformers coaxial to the cartridge for generating the survey current and for detecting the received current from the receive electrode. A plurality of receiver electrodes may be employed to provide simultaneous directional resistivity information from several directions around the wellbore, which may be used for detecting the presence of a nearby contrasting formation. Methods are provided for using this logging system to determine the direction and proximity of a contrasting resistivity layer, for determining apparent homogeneous resistivity of the formations surrounding the system, and for determining the dip and strike of formations intersected by the wellbore.
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Citations
23 Claims
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1. A resistivity logging system for use in measurement while drilling operations wherein the logging system is located in a down-hole assembly near a drill bit while a well is being drilled, the logging system comprising:
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a drill collar having a selected length; a transmitter sub connected to one end of the drill collar, the transmitter sub having an insulating layer that electrically isolates a first portion of the transmitter sub from a second portion of the transmitter sub, wherein the first portion of the transmitter sub includes a first conductive material on a first inner annular surface of the first portion, and the second portion of the transmitter sub includes a second conductive material disposed on a second inner annular surface of the second portion; a receiver sub connected to a second end of the drill collar, the receiver sub including at least one receiver electrode disposed over a selected portion of an outer annular surface of the receiver sub and at least one receiver electrode contact disposed on a selected portion of an inner annular surface of the receiver sub, the at least one receiver electrode coupled to the at least one receiver electrode contact via a conductive material disposed in the receiver sub, the conductive material being surrounded with insulating material; an instrument cartridge having a conductive body positionable within the drill collar and subs, the cartridge including; at least a first electrical contact for conductively coupling with the conductive material disposed on the first inner annular surface of the transmitter sub; at least a second electrical contact for conductively coupling with the conductive material disposed on the second inner annular surface of the transmitter sub; at least a third electrical contact for conductively coupling with the at least one receiver electrode contact; at least a fourth electrical contact for conductively coupling with a portion of the inner annular surface of the receiver sub that is independent of the conductive material and the insulating material; and current injection circuitry connected to inject current into the formation through the first electrical contact and current sensing circuitry connected to sense the current returned through the third electrical contact. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A resistivity logging system for use in a measurement while drilling operation, wherein the logging system is located in a drillstring proximate a bit, the logging system comprising:
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a transmitter sub for attaching to a drill collar, the transmitter sub including a transmitting electrode located on an external surface of the transmitter sub and electrically coupled via conductive material surrounded by insulating material to conductive material contact disposed on an internal annular surface of the transmitter sub; a receiver sub for attaching to the drill collar, the receiver sub including at least one directional receiving electrode located on an external surface of the receiver sub and electrically coupled via conductive material surrounded by insulating material to an electrical receiver contact located on an internal annular surface of the receiver sub; a retrievable instrument cartridge having a conductive body positionable within the drill collar, the transmitter sub and the receiver sub, the cartridge including; at least one electrical contact for conductively coupling with the transmitting electrode of the transmitter sub; at least a second electrical contact for conductively coupling with the receiving electrode of the receiver sub; current injection circuitry for injecting current into the formation through the transmitter sub; and current sensing circuitry for sensing the current received through the receiver sub. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification