Electricity: measuring and testing – Of geophysical surface or subsurface in situ – With radiant energy or nonconductive-type transmitter
Reexamination Certificate
1997-01-21
2001-09-11
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
With radiant energy or nonconductive-type transmitter
C324S369000
Reexamination Certificate
active
06288548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to measurement-while-drilling systems, and in particular relates to measurement-while-drilling systems which transmit or receive electromagnetic fields.
2. Description of the Prior Art
Measurement-while-drilling systems are now essential components of sophisticated exploration operations, and are utilized to provide real-time data pertaining to drilling conditions as well as the wellbore and surrounding formations. In particular, resistivity logs can be developed during drilling operations which, in some cases, provide a full substitute for the more conventional wireline electric logs. Other types of logging operations are also conducted in measurement-while-drilling systems, including neutron porosity measurements which provide a measure of the wellbore and formation porosity. The resistivity measurements can be utilized to provide a measure of the formation resistivity, the borehole diameter, the diameter of invasion of drilling mud into the formation, and to detect formation boundaries and formation changes.
In prior art systems, it is conventional to place the transmitting and receiving antennas of the measurement-while-drilling system within the tubular body of a drill collar or drill pipe member. Most commonly, a portion of the drill collar or drill pipe is “necked-down” (that is, milled or cut to a reduced radical dimension), to provide a relatively safe location for placement of the transmitting and receiving antennas. This, of course, structurally weakens the drill pipe or drill collar member, and renders it more susceptible to mechanical failure during drilling operations. In the prior art devices, the antennas are placed in or about the exterior surface of the drill pipe or drill collar member, since the drill pipe or drill collar member is typically formed from steel. Electromagnetic radiation cannot effectively be transmitted through steel tubulars, since the steel is a highly conductive material, and since the electromagnetic fields generate eddy currents in the conductive material which dissipate the field. The required exterior placement of the transmitted and receiving antennas exposes the antennas to the not-insubstantial forces which arise as the drill pipe or drill collar drags or otherwise engages the wellbore wall. Additionally, cuttings from the formation are circulated upward through the annulus between the drillstring and the wellbore. Cuttings which are propelled at high velocities can become lodged in the antenna assemblies and/or otherwise damage the antenna assemblies through abrasion. Additionally, the construction costs of a tool which has antennas which are part of the collar are high, since an expensive steel drill collar is machined with features which provide for the placement of antenna parts and for housing of the electronics which communicate with the antennas. Maintenance costs are also high for the prior art devices, especially since the tools include a heavy collar which can not be transported easily and since the tool can not be separated easily for replacement or servicing.
SUMMARY OF THE INVENTION
It is one objective of the present invention to provide an improved measurement-while-drilling system which utilizes a measurement tubular which is at least partially formed of a material which is non-conducting or poorly-conducting, and thus which allows the passage of electromagnetic fields both radially inward and radially outward relative to the measurement tubular.
It is another objective of the present invention to provide a measurement-while-drilling system which utilizes a transmissive measurement tubular which allows for the passage of electromagnetic fields through the tubular body, in combination with a measurement sonde which is disposed within the central bore of the measurement tubular, and which can be utilized to transmit interrogating electromagnetic signals into the formation and receive electromagnetic radiation from the borehole and surrounding formation to measure one or more borehole or formation characteristics.
These and other objectives are achieved as is now described in the context of formation resistivity measurement operations. When characterized as an apparatus, the present invention is directed to a measurement-while-drilling apparatus for use in a drillstring during drilling operations to interrogate a borehole and surrounding formation. The measurement-while-drilling apparatus includes a number of components which cooperate. A measurement sonde is provided and includes a transmitting member for generating an interrogating electromagnetic field for passage through the borehole and surrounding formation, and a receiving member for receiving an interrogating electromagnetic field after passage through the borehole and surrounding formation. A measurement tubular is also provided which includes a central bore which communicates with a central bore of the drillstring. A measurement tubular couples in the drillstring to locate the measurement sonde in a particular position, and to permit interrogation of the borehole and surrounding formation with the interrogating electromagnetic field. A means is provided for securing the measurement sonde in a particular location within the central bore of the measurement tubular. The measurement-while-drilling apparatus is operable in at least a transmission mode of operation and a reception mode of operation, which preferably occur simultaneously. During transmission operations, the interrogating electromagnetic field is generated by the measurement sonde and radiated outward from the measurement sonde and through the measurement tubular into the borehole and surrounding formation. During reception operations, the interrogating electromagnetic field passes from the borehole and surrounding formation through the measurement tubular for detection by the receiving member. In the preferred embodiment transmission and reception operations occur simultaneously.
In one particular embodiment, the measurement tubular comprises a solid cylindrical tubular formed of either non-conducting or poorly-conducting material which allows for the inward and outward passage of electromagnetic fields. In another embodiment, the measurement tubular includes a plurality of axial slots in a steel skeletal structure which are filled with non-conducting or poorly-conducting material, which allow for the passage of the interrogating electromagnetic field from the central bore of the measurement tubular to the borehole and surrounding formation. The most typical application of the present invention requires that the measurement tubular be a drill collar member for coupling at a lowermost portion of a drillstring.
In the preferred embodiment of the present invention, the measurement sonde includes a retrieval member which allows for (1) retrieval of the measurement sonde from the measurement tubular drilling operations without substantial interference with the drilling operations, and (2) placement of the measurement sonde in the measurement tubular during drilling operations without substantial interference with drilling operations.
When characterized as a method, the present invention is directed to a method of interrogating a borehole and surrounding formation during drilling operations, and includes a number of method steps. A measurement tubular is provided which is formed at least partially of a material which allows substantially unimpeded passage of electromagnetic fields, and which includes a central bore. A measurement sonde is provided. The measurement sonde includes a transmitting member for generating an interrogating electromagnetic field for passage through the borehole and surrounding formation, and a receiving member for receiving an interrogating an electromagnetic field after passage through the borehole and surrounding formation. The measurement sonde is secured within the central bore of the measurement tubular. The measurement tubular is coupled in a selected location within a drillstring.
Thompson Larry W.
Wisler Macmillan M.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
Snow Walter E.
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