Communications: electrical – Wellbore telemetering or control – Using a specific transmission medium
Reexamination Certificate
1998-12-22
2002-05-21
Edwards, Timothy (Department: 2735)
Communications: electrical
Wellbore telemetering or control
Using a specific transmission medium
C340S853300, C340S855100, C340S855200, C367S082000
Reexamination Certificate
active
06392561
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a downhole data transmission or telemetry system and method for communicating information axially along a drill string. More particularly, the present invention relates to a downhole short hop telemetry system and method, to be used with a measurement-while-drilling (MWD) system, for communicating information unidirectionally or bidirectionally between a sensor located near a drilling bit and the system axially along or through the components of the drill string.
BACKGROUND OF INVENTION
Directional drilling involves controlling the direction of a borehole as it is being drilled. Since boreholes are drilled in three dimensional space, the direction of a borehole includes both its inclination relative to vertical as well as its azimuth. Usually the goal of directional drilling is to reach a target subterranean destination with the drill string, typically a potential hydrocarbon producing formation.
In order to optimize the drilling operation, it is often desirable to be provided with information concerning the environmental conditions of the surrounding formation being drilled and information concerning the operational and directional parameters of the downhole motor drilling assembly including the drilling bit. For instance, it is often necessary to adjust the direction of the borehole frequently while directional drilling, either to accommodate a planned change in direction or to compensate for unintended and unwanted deflection of the borehole. In addition, it is desirable that the information concerning the environmental, directional and operational parameters of the drilling operation be provided to the operator on a real time basis. The ability to obtain real time data measurements while drilling permits a relatively more economical and more efficient drilling operation.
For example, the performance of the downhole motor drilling assembly, and in particular the downhole motor, and the life of the downhole motor may be optimized by the real time transmission of the temperature of the downhole motor bearings or the rotations per minute of the drive shaft of the motor. Similarly, the drilling operation itself may be optimized by the real time transmission of environmental or borehole conditions such as the measurement of natural gamma rays, borehole inclination, borehole pressure, resistivity of the formation and weight on bit. Real time transmission of this information permits real time adjustments in the operating parameters of the downhole motor drilling assembly and real time adjustments to the drilling operation itself.
Accordingly, various measurement-while-drilling (MWD) systems have been developed that permit downhole sensors to measure real time drilling parameters and to transmit the resulting information or data to the surface substantially instantaneously with the measurements. For instance, MWD mud pulse telemetry systems transmit signals from an associated downhole sensor to the surface through the drilling mud in the drill string. More particularly, pressure or acoustic pulses, modulated with the sensed information from the downhole sensor, are applied to the mud column and are received and demodulated at the surface. The downhole sensor may include various sensors such as gamma ray, resistivity, porosity or temperature sensors for measuring formation characteristics or other downhole parameters. In addition, the downhole sensor may include one or more magnetometers, accelerometers or other sensors for measuring the direction or inclination of the borehole, weight-on-bit or other drilling parameters.
Typically, MWD systems, such as the MWD mud pulse telemetry system, are located above the downhole motor drilling assembly. For instance, when used with a downhole motor, the MWD mud pulse telemetry system is typically located above the motor so that it is spaced a substantial distance from the drilling bit in order to protect or shield the electronic components of the MWD system from the effects of any vibration or centrifugal forces emanating from the drilling bit. Further, the downhole sensors associated with the MWD system are typically placed in a non-magnetic environment by utilizing monel collars in the drill string below the MWD system.
Thus, the MWD system may be located a significant distance from the drilling bit. As a result, the environmental information measured by the MWD system may not necessary correlate with the actual conditions surrounding the drilling bit. Rather, the MWD system is responding to conditions which are substantially spaced from the drilling bit. For instance, a conventional MWD system may have a depth lag of up to or greater than 60 feet. As a result of this information delay, it is possible to drill completely through a potential hydrocarbon producing formation before detecting its presence, requiring costly corrective procedures.
In response to this undesirable information delay or depth lag, various near bit sensor systems or packages have been developed which are designed to be placed adjacent or near the drilling bit. The near bit system permits the detection of the potential hydrocarbon producing formation almost immediately upon its penetration, minimizing the need for unnecessary drilling and service costs. The drilling operation, including the trajectory of the drilling bit, may then be adjusted in response to the sensed information.
However, in order to use a near bit sensor system and permit real time monitoring and adjustment of drilling parameters, a system or method must be provided for transmitting the measured data or sensed information from the downhole sensor either directly to the surface or to a further MWD system for subsequent transmission to the surface. Various attempts have been made in the prior art to transmit the information directly or indirectly to the surface. However, none of these attempts have provided a fully satisfactory solution.
Various systems have been developed for communicating or transmitting the information directly to the surface through an electrical line, wireline or cable to the surface. These hard-wire connectors provide a hard-wire connection from the drilling bit to the surface, which has a number of advantages. For instance, these connections typically permit data transmission at a relatively high rate and permit two-way or bidirectional communication. However, these systems also have several disadvantages.
First, a wireline or cable must be installed in or otherwise attached or connected to the drill string. This wireline or cable is subject to wear and tear during use of the system and thus, may be prone to damage or even destruction during normal drilling operations. For instance, the downhole motor drilling assembly may not be particularly suited to accommodate such wirelines running through the motor, with the result that the wireline sensors may not usually be located in close proximity to the drilling bit. Further, the wireline may be exposed to excessive stresses at the point of connection between the sections of drill pipe comprising the drill string. As a result, the system may be somewhat unreliable and prone to failure, which may result in costly inspection, servicing and replacement of the wireline. In addition, the presence of the wireline or cable may require a change in the usual drilling equipment and operational procedures. The downhole motor drilling assembly may need to be particularly designed to accommodate the wireline. As well, the wireline may need to be withdrawn and replaced each time a joint of pipe is added to the drill string. These disadvantages result in a relatively complex and unreliable system for transmitting the sensed information.
Systems have also been developed for the transmission of acoustic or seismic signals or waves through the drill string or surrounding formation. The acoustic or seismic signals are generated by a downhole acoustic or seismic generator. However, a relatively large amount of power is typically required downhole in order to generate a sufficient signal such that it i
Davies Evan L.
Donison Gary L.
Wiecek Boguslaw
Dresser Industries Inc.
Edwards Timothy
Kuharchuk Terrence N.
McCully Michael D.
Shull William
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