Communications: electrical – Wellbore telemetering or control – Repeater in subsurface link
Reexamination Certificate
1997-12-03
2001-04-17
Horabik, Michael (Department: 2735)
Communications: electrical
Wellbore telemetering or control
Repeater in subsurface link
C340S853100, C367S082000, C166S064000
Reexamination Certificate
active
06218959
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to downhole telemetry and, in particular to, the use of fail safe downhole signal repeaters for communicating signals carrying information between surface equipment and downhole equipment.
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 production.
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 increase 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 is 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 is connected to the ground at the surface where the electromagnetic data is picked up and recorded. It has been found, however, that in deep or noisy well applications, conventional electromagnetic systems are unable to generate a signal with sufficient intensity to reach the surface.
Therefore, a need has arisen for a system that is capable of telemetering real time information in a deep or noisy well between surface equipment and downhole equipment. A need has also arisen for a signal repeater that digitally processes the information to determine whether the signal is intended for that repeater. Further, a need has arisen for a fail safe repeater system that is capable of transmitting information between surface equipment and downhole equipment even in the event of a repeater failure.
SUMMARY OF THE INVENTION
The present invention disclosed herein uses fail safe signal repeaters that amplify and process signals carrying information in a system capable of transmitting information between surface equipment and downhole equipment even in the event of a repeater failure. The system and method of the present invention provide for real time communication from downhole equipment to the surface and for the telemetry of information and commands from the surface to downhole tools disposed in a well.
The system and method of the present invention utilize at least two repeaters which, for convenience of illustration, will be referred to as first and second repeaters. The first and second repeaters are disposed within a wellbore and receive a first signal carrying information. A memory device within the second repeater stores the information carried in the first signal until a timer device within the second repeater triggers the second repeater to retransmit the information. The timer device will trigger the retransmission of the information, after a predetermined time period, unless the second repeater has detected a third signal carrying the information transmitted by the first repeater. Thus, even if the first repeater is inoperable, the information carried in the first signal is retransmitted by the second repeater. If the first repeater transmits the third signal carrying the information within the predetermined time period and the third signal carrying the information is detected by the second repeater, the second repeater will discard the information stored in the memory device and process the information carried in the third signal.
The first and second repeaters of the present invention include electronics packages. The electronics packages transform the first signal into an electrical signal, convert the information carried in the electrical signal from an analog format to a digital format, process the information and convert the information carried in the electrical signal from a digital format to an analog format. The electronics packages also determine whether the first signal is intended for the first or the second repeater. Additionally, the electronics packages determine whether the first signal is carrying the information and whether the information carried in the first signal is accurate. The electronics packages also attenuate noise in the electrical signal to a predetermined voltage, amplify the electrical signal to a predetermined voltage, eliminate noise in the electrical signal in a predetermined frequency range and eliminate the unwanted frequencies above and below the desired frequency.
In one embodiment of the present invention, the first and second repeaters may each include an electromagnetic receiver and an electromagnetic transmitter or may include an electromagnetic transceiver.
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Edwards, Jr. Timothy
Halliburton Energy Service,s Inc.
Horabik Michael
McCully Michael D.
Youst Lawrence R.
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