Communications: electrical – Wellbore telemetering or control – Using a specific transmission medium
Reexamination Certificate
1997-10-31
2001-03-27
Horabik, Michael (Department: 2735)
Communications: electrical
Wellbore telemetering or control
Using a specific transmission medium
C340S853100, C340S854300, C367S081000, C073S152450
Reexamination Certificate
active
06208265
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to downhole telemetry and, in particular to, an electromagnetic signal pickup apparatus that substantially reduces the attenuation of an electromagnetic signal in the region near an electromagnetic pickup probe.
BACKGROUND OF THE INVENTION
Without limiting the scope of the invention, its background is described in connection with transmitting downhole data to the surface during measurements while drilling (MWD), as an example. It should be noted that the principles of the present invention are applicable not only during drilling, but throughout the life of a wellbore including, but not limited to, during logging, testing, completing and producing the well.
Heretofore, in this field, a variety of communication and transmission techniques have been attempted to provide real time data from the vicinity of the bit to the surface during drilling. The utilization of MWD with real time data transmission provides substantial benefits during a drilling operation. For example, continuous monitoring of downhole conditions allows for an immediate response to potential well control problems and improves mud programs.
Measurement of parameters such as bit weight, torque, wear and bearing condition in real time provides for a more efficient drilling operations. In fact, faster penetration rates, better trip planning, reduced equipment failures, fewer delays for directional surveys, and the elimination of a need to interrupt drilling for abnormal pressure detection is achievable using MWD techniques.
At present, there are four major categories of telemetry systems that have been used in an attempt to provide real time data from the vicinity of the drill bit to the surface, namely mud pressure pulses, insulated conductors, acoustics and electromagnetic waves.
In a mud pressure pulse system, the resistance of mud flow through a drill string is modulated by means of a valve and control mechanism mounted in a special drill collar near the bit. This type of system typically transmits at 1 bit per second as the pressure pulse travels up the mud column at or near the velocity of sound in the mud. It has been found, however, that the rate of transmission of measurements is relatively slow due to pulse spreading, modulation rate limitations, and other disruptive limitations such as the requirement of mud flow.
Insulated conductors, or hard wire connection from the bit to the surface, is an alternative method for establishing downhole communications. This type of system is capable of a high data rate and two way communication is possible. It has been found, however, that this type of system requires a special drill pipe and special tool joint connectors which substantially increases the cost of a drilling operation. Also, these systems are prone to failure as a result of the abrasive conditions of the mud system and the wear caused by the rotation of the drill string.
Acoustic systems have provided a third alternative. Typically, an acoustic signal is generated near the bit and is transmitted through the drill pipe, mud column or the earth. It has been found, however, that the very low intensity of the signal which can be generated downhole, along with the acoustic noise generated by the drilling system, makes signal detection difficult. Reflective and refractive interference resulting from changing diameters and thread makeup at the tool joints compounds the signal attenuation problem for drill pipe transmission.
The fourth technique used to telemeter downhole data to the surface uses the transmission of electromagnetic waves through the earth. A current carrying downhole data are input to a toroid or collar positioned adjacent to the drill bit or input directly to the drill string. When a toroid is utilized, a primary winding, carrying the data for transmission, is wrapped around the toroid and a secondary is formed by the drill pipe. A receiver, typically a conductive rod or probe, is inserted into the ground at the surface where the electromagnetic signal is picked up and the data carried therein is processed. It has been found, however, that cracking in the earth around the probe and discontinuities in the contact between the probe and the earth create a high resistivity interface between the probe and the earth that significantly attenuates the strength of the electromagnetic waves which, in turn, greatly reduces the allowable distance between the transmitter and the receiver. Additionally, poor contact between the probe and the earth serves as a source of unwanted noise.
Therefore, a need has arisen for a system that is capable of telemetering real time data from the vicinity of the drill bit in a deep or noisy well using electromagnetic waves to carry the information to the surface. A need has also arisen for an electromagnetic pickup system that can receive electromagnetic wave from a transmitter at a great distance without attenuating the signal at the interface between the probe and the earth.
SUMMARY OF THE INVENTION
The present invention disclosed herein comprises a electromagnetic signal pickup apparatus that utilizes a probe for receiving electromagnetic signals carrying information and a method for use of the same. The apparatus and method of the present invention provide for real time communication between downhole equipment and the surface using electromagnetic waves to carry information. The apparatus and method of the present invention overcome the attenuation of the electromagnetic signals caused by the high resistivity interface typically associated with cracking in the earth around the probe and discontinuities in the contact between the probe and the earth, thereby greatly increasing the allowable distance between the transmitter and the electromagnetic signal pickup apparatus.
The electromagnetic pickup apparatus of the present invention comprises a probe that is positioned in a bore hole or trench in the earth. The bore hole has a length and diameter sufficient for the insertion of the probe such that the probe is in a spaced apart relationship with the sides of the bore hole creating an annulus therebetween. Alternatively, the trench has a length and depth sufficient for receiving the probe.
A conductive backfill composition is placed around the probe to substantially surround the probe and to be in intimate contact with the probe and the earth. The conductive backfill composition thereby establishes a highly electrically conductive region around the probe that fills any crack in the earth and prevents any discontinuities in the electrical contact between the probe and the earth. This highly electrically conductive region of conductive backfill composition substantially reduces the attenuation of a received electromagnetic signal.
The conductive backfill composition may comprise a carbonaceous material such as graphite or a calcine fluid petroleum coke. The conductive backfill composition may be sized to less than 16 mesh, i.e., pass through a Tyler standard number 16 sieve.
The method of the present invention reduces the attenuation of a received electromagnetic signal. The method comprises drilling a bore hole or digging a trench in the earth and inserting the probe into the bore hole or trench. The probe has a spaced apart relationship with the sides of the bore hole forming an annulus that is filled with a conductive backfill composition. Alternatively, the probe is placed directly in the trench or on a layer of conductive backfill composition already in the trench. The conductive backfill composition is then poured on top of the probe.
In either case, the conductive backfill composition is oriented to create intimate contact with the probe and the earth. The conductive backfill composition creates a highly conductive region between the probe and the earth, thereby substantially increasing the allowable distance between the transmitter and the electromagnetic pickup device.
REFERENCES:
patent: 2354887 (1944-08-01), Silverman et al.
patent: 2364957 (1944-12-01), Douglas
patent: 2425868 (1947-08-01), Dill
Edwards, Jr. Timothy
Halliburton Energy Service,s Inc.
Herman Paul I.
Horabik Michael
Youst Lawrence R.
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