Patent Application
20110017512
Not applicable.
1. Technical Field
The present disclosure relates to wellbore communication systems and particularly to electromagnetic systems and methods for generating and transmitting data signals between the surface of the earth and a bottom hole assembly.
2. Background Art
Wells are generally drilled into the ground to recover natural deposits of hydrocarbons and other desirable materials trapped in geological formations in the Earth's crust. A well is typically drilled using a drill bit attached to the lower end of a drill string. The well is drilled so that it penetrates the subsurface formations containing the trapped materials and the materials can be recovered.
At the bottom end of the drill string is a “bottom hole assembly” (“BHA”). The BHA includes the drill bit along with sensors, control mechanisms, and the required circuitry. A typical BHA includes sensors that measure various properties of the formation and of the fluid that is contained in the formation. A BHA may also include sensors that measure the BHA's orientation and position.
The drilling operations may be controlled by an operator at the surface or operators at a remote operations support center. The drill string is rotated at a desired rate by a rotary table, or top drive, at the surface, and the operator controls the weight-on-bit and other operating parameters of the drilling process.
Another aspect of drilling and well control relates to the drilling fluid, called “mud”. The mud is a fluid that is pumped from the surface to the drill bit by way of the drill string. The mud serves to cool and lubricate the drill bit, and it carries the drill cuttings back to the surface. The density of the mud is carefully controlled to maintain the hydrostatic pressure in the borehole at desired levels.
In order for the operator to be aware of the measurements made by the sensors in the BHA, and for the operator to be able to control the direction of the drill bit, communication between the operator at the surface and the BHA is necessary. A “downlink” is a communication from the surface to the BHA. Based on the data collected by the sensors in the BHA, an operator may desire to send a command to the BHA. A common command is an instruction for the BHA to change the direction of drilling.
Likewise, an “uplink” is a communication from the BHA to the surface. An uplink is typically a transmission of the data collected by the sensors in the BHA. For example, it is often important for an operator to know the BHA orientation. Thus, the orientation data collected by sensors in the BHA is often transmitted to the surface. Uplink communications are also used to confirm that a downlink command was correctly understood and executed.
One common method of communication is called “mud pulse telemetry.” Mud pulse telemetry is a method of sending signals, either downlinks or uplinks, by creating pressure and/or flow rate pulses in the mud. These pulses may be detected by sensors at the receiving location. For example, in a downlink operation, a change in the pressure or the flow rate of the mud being pumped down the drill string may be detected by a sensor in the BHA. The pattern of the pulses, such as the frequency, the phase, and the amplitude, may be detected by the sensors and interpreted so that the command may be understood by the BHA.
Mud pulse telemetry systems are typically classified as one of two species depending upon the type of pressure pulse generator used, although “hybrid” systems have been disclosed. The first species uses a valving “poppet” system to generate a series of either positive or negative, and essentially discrete, pressure pulses which are digital representations of transmitted data. The second species, an example of which is disclosed in U.S. Pat. No. 3,309,656, comprises a rotary valve or “mud siren” pressure pulse generator which repeatedly interrupts the flow of the drilling fluid, and thus causes varying pressure waves to be generated in the drilling fluid at a carrier frequency that is proportional to the rate of interruption. Downhole sensor response data is transmitted to the surface of the earth by modulating the acoustic carrier frequency. A related design is that of the oscillating valve, as disclosed in U.S. Pat. No. 6,626,253, wherein the rotor oscillates relative to the stator, changing directions every 180 degrees, repeatedly interrupting the flow of the drilling fluid and causing varying pressure waves to be generated.
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The surface system processor may be implemented using any desired combination of hardware and/or software. For example, a personal computer platform, workstation platform, etc. may store on a computer readable medium (e.g., a magnetic or optical hard disk, random access memory, etc.) and execute one or more software routines, programs, machine readable code or instructions, etc. to perform the operations described herein. Additionally or alternatively, the surface system processor may use dedicated hardware or logic such as, for example, application specific integrated circuits, configured programmable logic controllers, discrete logic, analog circuitry, passive electrical components, etc. to perform the functions or operations described herein.
Still further, while the surface system processor can be positioned relatively proximate to the drilling rig (i.e., substantially co-located with the drilling rig), some part of or the entire surface system processor may alternatively be located relatively remotely from the rig. For example, the surface system processor may be operationally and/or communicatively coupled to the wellbore telemetry component 18 via any combination of one or more wireless or hardwired communication links (not shown). Such communication links may include communications via a packet switched network (e.g., the Internet), hardwired telephone lines, cellular communication links and/or other radio frequency based communication links, etc. using any desired communication protocol.
Additionally one or more of the components of the BHA may include one or more processors or processing units (e.g., a microprocessor, an application specific integrated circuit, etc.) to manipulate and/or analyze data collected by the components at a downhole location rather than at the surface.
Electromagnetic MWD telemetry uses an electric dipole (voltage applied across an insulated gap) as a downhole source. The received signal at the surface is the voltage sensed between two or more ground electrodes. That is, receivers for electromagnetic MWD telemetry systems generally comprise grounding stakes, and the signal is the voltage measured at the stake with reference to the rig structure. Low frequency signals are used to overcome attenuation. The system is totally reversible: by forcing a current across the two surface electrodes, a corresponding voltage can be sensed downhole across the insulating gap. This telemetry system does not require mud flow for telemetry operations and is therefore less intrusive to rig operations. Examples of electromagnetic telemetry systems using electrodes separated by an insulated gap is found in U.S. Pat. No. 5,642,051 and U.S. Pat. No. 7,080,699.
This prior art method is limited, however, to land use because offshore the signal is short circuited by the salt water. Limitations of electromagnetic MWD are related to depth, formation resistivity, and the presence of insulating layers like anhydrite streaks. Signal reception is difficult and pick-up (receiver) electrodes have to be buried sufficiently deep to avoid the shorting effect of the salt water and the low resistivity of shallow sediments. For at least those reasons, electromagnetic MWD telemetry is seldom used offshore.
Magnetometers (search coils) have been proposed to sense the magnetic field induced by the telemetry currents. However, this has not been successful to the point of commercial application. Experiments have been performed using subsea magnetometers, but the results have not been very successful.
The present disclosure relates to a telemetry system. The telemetry system includes a first downhole device capable of transmitting and/or receiving a signal disposed in a first wellbore, an electronics control system located at or near the top of the first wellbore, a cable disposed in the first wellbore that provides signal communication between the first downhole device and the electronics control system, and a second downhole device capable of transmitting and/or receiving a signal disposed in a second wellbore. The signal is passed through the cable between the first downhole device and the electronics control system. From there, the signal may be re-transmitted to a desired location.
Other aspects and advantages of the invention will become apparent from the following description and the attached claims.
So that the above recited features and advantages of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
It is to be understood that the drawings are to be used for the purpose of illustration only, and not as a definition of the metes and bounds of the invention, the scope of which is to be determined only by the scope of the appended claims.
Specific embodiments of the invention will now be described with reference to the figures. Like elements in the various figures will be referenced with like numbers for consistency. In the following description, numerous details are set forth to provide an understanding of the present disclosure. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible.
The following terms have a specialized meaning in this disclosure. While many are consistent with the meanings that would be attributed to them by a person having ordinary skill in the art, the meanings are also specified here.
In this disclosure, “fluid communication” is intended to mean connected in such a way that a fluid in one of the components may travel to the other. For example, a bypass line may be in fluid communication with a standpipe by connecting the bypass line directly to the standpipe. “Fluid communication” may also include situations where there is another component disposed between the components that are in fluid communication. For example, a valve, a hose, or some other piece of equipment used in the production of oil and gas may be disposed between the standpipe and the bypass line. The standpipe and the bypass line may still be in fluid communication so long as fluid may pass from one, through the interposing component or components, to the other.
A “drilling system” typically includes a drill string, a BHA with sensors, and a drill bit located at the bottom of the BHA. Mud that flows to the drilling system must return through the annulus between the drill string and the borehole wall. In the art, a “drilling system” may be known to include the rig, the rotary table, and other drilling equipment, but in this disclosure it is intended to refer to those components that come into contact with the drilling fluid.
“Signal communication” means the ability or capacity to transmit or receive a signal between two or more devices such as transmitters, receivers, transceivers, or fiber optic devices. The signal may be carried in or on, for example, an electrical cable, a fiber optic cable, or it may pass wirelessly between the devices. Signal communication further includes data and/or power transmission.
Most offshore fields are developed by drilling multiple deviated and horizontal drainage wells. Several tens, perhaps as many as a hundred, drainage wells are drilled from a single surface location. Prior to developing the field, however, one or more mostly vertical appraisal wells are typically drilled to evaluate the subsurface formations. After a comprehensive logging and testing program, appraisal wells are often plugged and abandoned (P&A).
It should be noted that, while the description above and what follows speaks mostly in terms of downhole receivers used in an uplink mode, by reciprocity the receivers can be replaced by transmitters, and vice versa, and the tool may be used in a downlink mode. That is, in uplink mode, for example, information from an ancillary tool in another wellbore may be transmitted to the receivers in the appraisal well, and that information is communicated to the surface or seafloor between devices that are in signal communication with one another (e.g., using the cable or perhaps wireless telemetry). However, the invention can equally be used in downlink mode. For example, instructions and/or data can be sent from the surface or seafloor to a downhole device that is in signal communication with an uphole device. That downhole device could then convey the command(s) and/or data to an ancillary tool in another wellbore. It is to be understood that the present description may speak in terms of receivers, and the examples may illustrate an uplink mode, but that is for ease of description only and the invention is intended to encompass the use of transmitters, receivers, and/or transceivers configured and used in a downlink mode as well.
As indicated above, downhole receivers 106 are connected to wellhead 104 by a cable 102 that is deployed as part of the P&A program. Cable 102 terminates at the subsea wellhead 104 where electronics and power modules 108 are installed. For example, a battery-powered electronic control system 108 may be installed at the sea floor 105 on or near wellhead 104. Signal from the downhole receivers 106 are sensed, amplified, and decoded, and subsequently transmitted to a surface location using, for example, an umbilical or standard acoustic telemetry. Standard acoustic telemetry is well suited for underwater applications. Acoustic telemetry uses acoustic energy to convey a signal. The acoustic energy can pass, for example, through drill pipe or casing, or through a fluid such as the water above the seafloor. Alternatively, communication to a surface location can be achieved using an umbilical. Examples of using acoustic telemetry or an umbilical as a communication link to the surface are described in U.S. Pat. No. 7,261,162. Standard existing techniques for subsea instrumentation may be used for maintenance or battery servicing.
In operation, when drilling a drainage well 110, an electromagnetic telemetry tool 112 may be deployed as part of the BHA. The transmitted signal from electromagnetic telemetry tool 112 is detected by receivers 106 in appraisal well 101, relayed by cable 102 to wellhead 104, and re-transmitted to a surface location. The surface location can be any desired location; the term is intended to encompass any location remote from the electronic control system 108. This process is illustrated in the flowchart of
The standard telemetry used to re-broadcast the MWD telemetry signals from the seabed to the surface may also be used for downlinking operations. In the case where downlinking is needed, a command sent to electronics control system 108 causes electronic control system 108 to send power downhole and a current is injected, for example, between one of the electrodes 106 and an electric ground (e.g., casing) or across two electrodes 106. For example, in an uncased hole, two or more spaced electrodes 106 can be used. In a partially cased well, one electrode placed below the casing and the casing itself will serve. In a cased well, an insulated gap may be built into the casing string and the separated portions of casing can be used. The resulting electric field in the formation is sensed by electromagnetic telemetry tool 112 and the command passed on to the MWD tool.
If desired, the system could operate in a full duplex mode, for instance, by operating at different frequencies for transmitting and receiving. Data or commands may be encoded using, for example, frequency, phase, or amplitude modulation, or a combination of those. That is, the signal can be modulated to encode data using, for example, methods known in digital communications. The uplink and downlink modes could be operated simultaneously or sequentially.
The investment corresponding to the installation of the permanent receivers 106 may be amortized over the entire development. This technique would be adaptable to high pressure, high temperature (HPHT) fields in that the electromagnetic telemetry system is much simpler than a mud pulse telemetry system, and therefore more likely to be reliable in a HPHT application.
This description is intended for purposes of illustration only and should not be construed in a limiting sense. The scope of this invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. “A,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded. While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be envisioned that do not depart from the scope of the invention as disclosed herein.
