WO2000030299A1 - Transmitting information over a communication link - Google Patents

Abstract

A communications system for use in a well includes a communications link and a plurality of nodes coupled to the communications link. The plurality of nodes include a transmitting node and responding nodes. The transmitting node adapted to transmit a predefined command (e.g., a special read command), and the responding nodes each includes a control device adapted to respond to the predefined command by transmitting a data block.

Description

TRANSMITTING INFORMATION OVER A COMMUNICATION LINK

The invention relates to transmitting information over a communication link in a well.

After a wellbore has been drilled, various completion operations may be performed in the wellbore, in which equipment including packers, valves, flow tubes, and other devices may be set to control fluid production from one or more zones in the well, which may be a vertical, deviated, or multilateral well. With advances in technology, sensors and control devices may be placed downhole to monitor and to adjust downhole conditions. An example system that monitors downhole conditions may include various downhole gauges and sensors that are capable of monitoring temperature, pressure,, and flow information. Using a communications link, such as an acoustic data link or a digital telemetry link, data gathered by the gauges and sensors may be sent to the surface to control boxes. The data may then be processed to determine the conditions downhole so that production may be improved and potential reservoir problems may be avoided. In addition to gauges and sensors, other downhole systems may include control devices that are addressable to adjust equipment settings.

To allow communications between nodes (including a surface node and one or more downhole nodes) coupled to a communications link, a communications protocol is used. One such communications protocol is the Modbus protocol, originally developed by MODICON, now a part of Schneider Automation Inc. in Andover Massachusetts. The protocol has been widely utilized, with some slight adaptations by other companies. Controllers coupled to a Modbus communications link communicate according to a master-slave protocol, in which one device (the master) initiates a transaction (e.g., a query) and another device (the slave) responds to the query by supplying the requested data to the master or by taking the action requested in the query. In a system used with a well, a master may include a controller in a surface node, and slaves may include controllers in downhole nodes. With the Modbus protocol, the master can address individual slaves or it can initiate a broadcast message to all slaves. A slave may respond to queries that are addressed to them individually. However, responses are not returned by slaves to broadcast queries from the master. Each downhole node includes various types of information that the surface node may wish to access, including the states of various storage elements (such as registers) and other components in a downhole node. To retrieve blocks of data from several downhole nodes, a corresponding number of read queries are needed to retrieve the information. For example, if information from five downhole nodes are desired, then five read queries are needed to retrieve blocks of data from the five downhole nodes. Thus, the command down and data up sequence may be as follows: read block 1 followed by data from block 1 ; read block 2 followed by data from block 2; read block 3 followed by data from block 3; read block 4 followed by data from block 4; and read block 5 followed by data from block 5. Thus, five read commands are transmitted downhole to the nodes, and five blocks of data are transmitted up the communications link to the surface node. As evident from this communications protocol, as the number of nodes grow, data traffic increases proportionally in the retrieval of data from the downhole nodes. Because of the typical lengths of a communications link in a wellbore (e.g., thousands to tens of thousands of feet), the communications rate over the link may be relatively slow, e.g.. about 600 baud. Due to the need for separate read queries to access information from multiple downhole nodes, data communications bandwidth may be reduced. Thus, a need exists for an improved communications system for linking multiple nodes.

In general, according to one embodiment, a method of communicating over a communications link in a well includes transmitting a query received at nodes coupled to the communications link. The nodes respond to the query by transmitting data blocks stored in each of the nodes over the communications link.

Other features will become apparent from the following description and from the claims. Fig. 1 is a diagram of a system in a well having multiple nodes coupled over a communications link. Figs. 2A-2C illustrate data streams sent by multiple downhole nodes according to some embodiments of the invention.

Fig. 3 is a block diagram of a portion of a downhole node according to an embodiment of the invention. Fig. 4 is a flow diagram of a sequence to retrieve information according to an embodiment.

In the following description, numerous details are set forth to provide an understanding of the present invention. However, it is to 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 may be possible.

According to some embodiments of the invention, a special command is defined to allow a master node coupled to a communications link to retrieve information from multiple slave nodes using the special command. The special command may include one of the following: a read command to one or more predefined addresses, a broadcast or multicast command, a write command to one or more predefined addresses, a configuration command to one or more predefined addresses, and other types of predefined commands. Once slave nodes decode the special command, each of the slave nodes may respond by providing a set of information. A general characteristic of the special command is that nodes receiving the command transmits some type of a response.

In the ensuing description, reference is made specifically to a special read command. It is to be understood, however, that other types of special commands or queries may also be utilized that require some type of response over the communications link from nodes coupled to the link. In one embodiment, communications over the communications link proceeds according to the Modbus protocol. The predefined special commands according to some embodiments may be commands defined by the Modbus protocol. However, instead of only one node responding to a special command, multiple nodes may respond to the special command according to some embodiments by successively transmitting responses to the special command. Thus, an advantage offered by such embodiments may be that an existing protocol is used for communications over a link while some or all of the nodes coupled to the link are configurable to respond to a special command to improve communications bandwidth.

In other embodiments, communications of the link may proceed according to other protocols, such as the HART (Highway Addressable Remote Transducer) Communication Protocol, provided by the Hart Communication Foundation in Austin, Texas; and the Foundation Fieldbus Protocol, provided by the Fieldbus Foundation in Austin, Texas. Communications may also proceed according to other protocols in further embodiments.

In a communications system located in the wellbore having multiple downhole nodes, a special read command transmitted by a surface node over the communications link may be responded to by each of the downhole nodes. In one embodiment, each node may be acting as though it is responding to a standard read command over the communications link. In other embodiments, the downhole nodes are responding to broadcast commands, multicast commands, special write commands, special configuration commands, or other commands.

The downhole nodes respond to the special read command serially, with a first node transmitting a first set of data, a second node transmitting a second set of data after the first transmission, and so forth. The first node responding to the command may also generate the header for all nodes, and the last node to transmit may also generate the trailer for all nodes.

In an alternative embodiment, it may be possible to ha\ e each node generate header and trailer information for itself with the additional requirement that the first node generates header information for all responding nodes and the last node generates trailer information for all responding nodes. This alternative embodiment may be advantageous in a noisy communications link.

Referring to Fig. 1 , in an example communications system according to an embodiment of the invention for use with a well 8, a surface node 10 may be coupled to multiple downhole nodes over a communications link 30 in the well 8, illustrated as five nodes 12, 14, 16, 18. and 20. In alternative embodiments, a larger or smaller number of downhole nodes may be coupled to the communications link 30. The nodes may include various types of control devices, including general -purpose and special-purpose controllers such as microprocessors, microcontrollers, application specific integrated circuits (ASICs), programmable gate arrays (PGAs), or other control devices, whether integrated or discrete. Such control devices are responsible for decoding commands transmitted on the communications link 30 and for generating responses, or optionally commands, on the communications link 30. In addition, each downhole node may be associated with a set of gauges and sensors to detect downhole conditions, including temperature, pressure, flow rates, and so forth. The well 8 may be a vertical or deviated well (or a combination of both) with one or more completion zones, or it may be a multilateral well. During production, it may be desirable for the surface node 10 to sample the states of various downhole nodes, including for example, information indicating downhole environmental conditions (e.g., temperature, pressure, and the like), flow rate, and states of various downhole equipment, such as packers, valves, and other devices. According to some embodiments, the surface node 10 is capable of transmitting a special read command to retrieve information from each of the downhole nodes. In response to the special read command, multiple downhole nodes serially transmit the requested data over the communications link 30 to the surface node 10. By utilizing a single special read command to retrieve multiple blocks of data from multiple nodes, the communications bandwidth over the link 30 may be increased.

An example sequence of data communication from the downhole nodes to the surface node 10 in response to the special read command is illustrated in Fig. 2A. In one example configuration, the downhole nodes 12, 14, 16. 18. and 20 are configured as nodes #1-5. respectively. In response to the special read command, node #1 first transmits header information 100 up the communications link 30. The header information 100 may identify the number of blocks expected in the transmission from the nodes #1-5 in response to the special read command. After the header information 100, node #1 transmits a first data block 102. After node #1 has transmitted its data block 102, node #2 transmits its data block 104. This is followed by data blocks 106, 108, and 1 10 from nodes #3, #4, and #5, respectively. Finally, the last node, node #5, transmits trailer information 1 12 to indicate that the end of data stream has been reached. The data stream illustrated in Fig. 2A is consistent with a data stream expected by the requesting master in a query-response type communications protocol such as the Modbus protocol. Basically, the data stream according to Fig. 2A includes a header, a body containing responsive data, and a trailer.

According to alternative embodiments, in addition to the general header 100 and general trailer 1 12 for all the nodes, each of the nodes may also transmit their own header and trailer information for improved data reliability in a noisy communications link.

Fig. 2B illustrates another example sequence according to an embodiment. In this other example, some of the nodes may be sampled more than once in response to the special read command. In the illustrated example, nodes #1 and 2 transmit their data blocks twice. Thus, after node #1 has sent the header information 100, it transmits its first data block 120. This is followed by data blocks 122, 124, 126, and 128 from nodes #2, #3, #4, #5, respectively. However, after node #5 has transmitted its data block 128, node #1 transmits its second data block 130. After node #1 has transmitted its second data block 130, node #2 also transmits its second data block 132. In this case, since node #2 is the last node to transmit data, it also transmits the trailer information 112. According to the example of Fig. 2B, a special read command may be used to retrieve data from all the nodes as well as retrieve data from some selected nodes at higher effective sampling rates than others. According to one embodiment, predefined parameters may be set in the downhole nodes to program how the nodes are to respond to the special read command. Some nodes may be configured to respond only once while others may be configured to respond more than once.

Fig. 2C illustrates another example sequence in which the downhole nodes are sampled continuously in response to the special read command; that is, no end to the response is specified. After node #1 transmits the header block 100, nodes #1-5 successively transmit data blocks 140, 142, 144, 146, and 148, respectively. Next, nodes #1-5 again successively transmit their data blocks, in this case blocks 150, 152, 154, 156, and 158. respectively. This is repeated continuously until the surface node 10 ends the transmissions by, for example, issuing some type of interrupt command. An advantage offered by this feature is that once the surface node 10 issues its request, the downhole nodes continue to transmit information without further intervention by the surface node. This may be advantageous where the surface operator desires to continuously monitor information such as downhole temperature, pressure, flow rates, and other data from the different zones in the well 8.

All or some of the downhole nodes may be configured by a setup sequence to transmit predetermined types and amounts of data. The downhole nodes may also store configuration information to determine when the downhole nodes are to begin data transmission in relation to the other downhole nodes. The setup sequence may be generated by the surface node 10 to indicate to each downhole node the type of information that is desired from that particular node. For example, the surface node 10 may request temperature and pressure information from node #1. For the other nodes, the surface node 10 may request other types of information. This is configured during the setup sequence so that the downhole nodes will respond with the requested information in response to the special read command. Other configuration information are also stored in the downhole nodes during the setup sequence. Once the setup sequence is performed, the surface node 10 does not need to generate another setup sequence until the surface node 10 wants to change the types or amounts of information or the sampling rates needed from the downhole nodes.

Referring to Fig. 3, certain components of a downhole node are illustrated. Each of the downhole nodes may be constructed the same way or with some variations or modifications. An interface block 200 couples the communications link 30 to the remaining circuitry in the downhole node. The interface block 200 may be, for example, a modem, a network interface card, or some other suitable interface circuit to manage communications with the link 30.

In the illustrated embodiment, the interface block 200 may be coupled to a bus 216 that is coupled to various elements, including a controller 202. The controller 202 is responsible for decoding commands transmitted down the communications link 30 as well as responding to these commands. Optionally, the controller 202 in some downhole nodes may be capable of generating commands or queries to transmit to other nodes coupled to the link 30. One of the commands that the controller 202 is able to decode is the special read command according to an embodiment. Various configuration registers are located in the downhole node that are accessible by the controller 202 over the bus 216 to determine how it is to respond to a special read command. These configuration registers may be programmed by the surface node during the setup sequence.

A first configuration register 204 stores an initial counter start value that is to be loaded into a decrement counter 206 in response to receipt of the special read command. The initial counter start value is loaded from the register 204 through a multiplexer 208 into the counter 206. The counter 206 is clocked by a signal DATAJBYTE, which is pulsed high by the controller 202 every time a transmitted data byte from another node is detected on the link 30 by the controller 202. Once it is loaded with the counter start value, the counter 206 decrements down to zero. The counter 206 is configured to count a predetermined number of data bytes (as indicated by the register 204) transmitted over the link 30 by another node before the current node starts transmitting its own set of data in response to the special read command. In alternative embodiments, an increment counter may be used instead of a decrement counter. For example, in the example sequence of Fig. 2 A. node #2 has to wait for the bytes in the data block 102 to be transmitted before it can transmit its own block 104. Similarly, node #5 has to wait for transmission of the bytes in data blocks 102, 104, 106, and 108 before it can transmit its own block 1 10. The counter start value in register 204 indicates when the controller 202 is to start transmitting data after the other data bytes have already been transmitted, as detected by the controller 202 through the interface block 200.

The downhole node may also store a counter reset value in another configuration register 218. The counter reset value is the reload value for multiple sampling of selected downhole nodes. Thus, in the sequence of Fig. 2B, nodes #1 and #2 will have a counter reset value that indicates the number of blocks that are to go by after the node has transmitted its data the first time. Thus, for example, for node #1 , the counter reset value will be a value representing the number of bytes of blocks 122- 128 transmitted by nodes #2-5, respectively, after node #1 has transmitted its first data block 120. Similarly, the counter reset value of node #2 represents the number of bytes in data blocks 124-130 transmitted by nodes #3. #4. #5. and #1 , respectively, in successive order after node #2 has transmitted its first data block 122. The counter reset value is selected by the multiplexer 208 for loading into the counter 206 after the previous transmission has occurred. In one embodiment, the counter 206 is loaded with the counter reset value in the register 218 after the controller 202 detects that the counter 206 has reached zero.

To prevent a downhole node from transmitting multiple times in response to a special read command, the counter reset value stored in the register 218 may be set such that the counter 206 contains at least the value one after the last node has sent its data. Thus, in the example sequence of Fig. 2A, the counter reset value stored in node #1 will be at least one greater than the number of bytes contained in blocks 104, 106, 108, 110, and 112. While the counter 206 in node #1 still contains a non-zero value, all bytes have been transmitted up the link 30 in response to the special read command. Consequently, the controller 202 in node #1 will not transmit again.

In the example of Fig. 2C in which continuous sampling of all the downhole nodes occurs, the counter reset value 218 is repeatedly loaded into the counter 206 by the controller 202 each time the counter 206 decrements down to zero. This ensures that the controller 202 in each node re-transmits another data block after the last node has finished transmitting its data block.

In further embodiments, a field in the register 218, or alternatively, a separate configuration register, may store a value indicating the number of times the controller 202 is to transmit data blocks in response to a special read command. In addition, a transmission wait time value may be stored in another configuration register 220 to represent the length of time in clock ticks that a node is to wait after the counter 206 has decremented to zero before beginning to transmit its data block. Thus, after the counter 206 counts to zero, indicating that the proper number of bytes have been transmitted over the communications link 30 by other nodes, the value in register 220 may be loaded into a wait counter 230. The wait counter 230 is clocked by a clock CLK. After the wait counter 230 decrements to zero, the controller 202 is allowed to begin transmitting its data. The added wait time is to allow an opportunity for the surface node 10 to issue an interrupt or another command to the downhole nodes between data block transmissions by the different nodes in response to the special read command.

The downhole node also includes another configuration register 222 to store a block packet size value. The block packet size represents the number of bytes that the current node is to transmit in response to the special read command. Information in the downhole node may be stored in one or more storage elements in the node, including one or more of the following: a memory 210, registers 212, and other storage devices 214. The memory 210 may include random access memories (RAMs) such as dynamic RAMs (DRAMs), synchronous DRAMs (SDRAMs), static RAMs (SRAMs), erasable and programmable read-only memories (EPROMs), electrically erasable and programmable read-only memories (EEPROMs), flash memories, and other types of integrated circuit (IC) memories. In addition, the downhole node may include a set of status registers 212 that are configured to store various status information. Other storage elements 214 may also be included to store other types of information in the downhole node. Each of the storage elements 210, 212, and 214 are coupled to the data bus 216 so that data from the storage elements may be retrieved by the controller 202. In some embodiments, the configuration registers discussed above may be part of the storage elements 210, 212, or 214. Thus, the block packet size value as specified in the register 222 indicates the number of bytes to be transferred from the storage elements 210, 212, and 214 over the data bus 216, which are in turn transferred to the communications link 30 through the interface block 200. The downhole node may also include a configuration register 224 to store the total packet count that is a value stored in a header block representing the number of bytes that are being sent in the current transmission by all responding nodes in response to the special read command. Thus, for example, the register 224 in node #1 (or another node that is the first node to transmit) may be stored with a value representing the total number of bytes that are going to be transmitted by the combination of all responding nodes. In the embodiment where only the first node transmits header information, the controller 202 of the other nodes may be configured to ignore contents of the total packet count register 224. In embodiments where each node transmits its own set of header and trailer information, the total packet count register 224 may contain a value representing the number of bytes that that particular node is transmitting. A block start address is stored in a configuration register 226 to represent the starting address of the bytes to be transmitted by the controller 202 in response to the special read command. In many cases, the bytes that are to be transmitted may not be stored contiguously in physical memory in the downhole node. The storage elements 210, 212, and 214 are accessed with physical addresses. Information to be transmitted in response to the special read command may come out of non-contiguous physical address locations from one or more of the memory 210. the status registers 212, and the other storage elements 214. To allow the controller 202 to retrieve the noncontiguous blocks of data from storage elements 210, 212, and 214 based only on a single block start address in register 226, an address translation array 232 may be preloaded with address translation values. The address translation array 232 may be configured to translate the sequential addresses starting from the block start address specified in the register 226 into the non-contiguous physical addresses corresponding to the desired locations in the storage elements 210, 212 and 214.

The registers 204, 218, 220, 222, 224, and 226 are loaded by a setup sequence performed by the surface node 210 over the communications link 30. In one embodiment, write commands may be issued over the communications link 30 to write to each of the configuration registers 204-220. In addition, the address translation array 232 may also be programmed by the setup sequence to convert consecutive virtual addresses starting from the block start address into non-contiguous physical addresses to access locations in the storage elements 210, 212, and 214. Depending on the features desired of the responding node, some of the components shown in Fig. 3 may be omitted from a downhole node. For example, a downhole node may be configured to recognize the special read command (or other special command) but is configured to respond with only one data block (i.e., these nodes do not include the multiple sampling feature). Further, some of the features described may be omitted or not used to allow communications over the link 30 to be compatible or consistent with existing communications protocols. In other embodiments, all of the features, and any variations or modifications of such features, may be implemented to achieve a flexible communications scheme.

A setup sequence is performed by the surface node when it first starts up and subsequently when the types of information needed from the downhole nodes or the node sampling rates need to be changed. Referring to Fig. 4, according to one embodiment, a data access sequence performed by the surface node 10 is illustrated. The surface node 10 first loads the configuration registers as well as the address translation array in each of the downhole nodes (at 302) to set up the downhole nodes to respond to a special read command. After the setup, the surface node 10 issues the special read command (at 304). Next, the surface node 10 determines (at 306) if it needs to send another new command down the communications link 30. If not, the surface node 10 waits to receive information (at 308), if any. If a new command needs to be sent, the surface node 10 issues (at 310) a new command in the transmit wait time periods between successive data block transmissions by the downhole nodes.

Next, the surface node 10 determines (at 312) if the end of the response stream has been received. If not, the surface node 10 performs the acts at 306, 308 and 310 until the end of stream has occurred. When that happens, the surface node 10 determines (at 314) if the special read command needs to be transmitted again. If so, acts 304-312 are repeated. If not, the data access is completed.

Other embodiments are also within the scope of the following claims. For example, other special commands besides a special read command may be utilized to retrieve information or other responses from nodes. Such other special commands may include broadcast commands, multicast commands, special write commands, special configuration commands, and so forth. In addition, although downhole nodes are described as the nodes responding to the special commands, it is contemplated that one or more surface nodes coupled to the communications link may also be configurable as slave devices that respond to commands on the link. In addition, any one of the nodes coupled to the communications link may be configured to transmit a special command that require some type of response from the nodes. Any of the nodes may also be configurable to issue a setup sequence to program the other nodes. Further, although the described communications system is used in a well, the same or a similar communications system may have other applications.

In further embodiments, the special commands may specify addresses of nodes that are to receive the special command, thus enabling a master node to select responding nodes. In addition, in other embodiments, certain of the nodes may act as gateways or routers that may be configured to direct the flow of the special commands. For example, in a multilateral well, such gateways or routers may direct the special commands down selected paths and not others. While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention. What is claimed is:

Claims

1. A method of communicating over a communications link in a well, comprising: transmitting a query; receiving the query at a plurality of devices coupled to the communications link; and responding, from the plurality of devices, to the query by transmitting data blocks stored in each of the devices over the communications link.

2. The method of claim 1 , further comprising accessing, in each of the devices, configuration information to determine the data block to transmit.

3. The method of claim 2, further comprising setting up the configuration information in each device.

4. The method of claim 1 , further comprising: a first device transmitting header information; and the devices successively transmitting data blocks after the header information.

5. The method of claim 4, wherein the header information contains a value identifying the amount of data in the data blocks.

6. The method of claim 4, further comprising a last device transmitting trailer information.

7. The method of claim 1 , comprising the devices successively transmitting data blocks in response to the query.

8. The method of claim 7, further comprising one or more of the devices transmitting data blocks multiple times in response to the query.

9. The method of claim 7, further comprising waiting predetermined time periods between successive transmissions by the devices.

10. The method of claim 9, further comprising transmitting another command in one of the predetermined time periods.

11. The method of claim 1, each downhole node monitoring for a predetermined amount of data to be transmitted over the communications link before the downhole node transmits its data block.

12. The method of claim 1 , wherein the query includes a read command having a predefined address.

13. The method of claim 1 , wherein the query includes a broadcast command.

14. The method of claim 1, comprising transmitting the query according to a Modbus protocol.

15. The method of claim 14, comprising responding to the query with a data stream consistent with the Modbus protocol.

16. A communications system for use in a well, comprising: a communications link; and a plurality of nodes coupled to the communications link, the plurality of nodes including a transmitting node and responding nodes, the transmitting node adapted to transmit a predefined command, and the responding nodes each including a control device adapted to respond to the predefined command by transmitting a data block, the responding nodes successively transmitting data blocks in response to each predefined command.

17. The communications system of claim 16, wherein each of the responding nodes includes configuration information accessible by the control device.

18. The communications system of claim 17, wherein the transmitting node is adapted to update the configuration information in each of the responding nodes.

19. The communications system of claim 16, wherein each of the responding nodes includes a counter loaded with a value to indicate the amount of data to be transmitted by other responding nodes before the control device transmits a data block.

20. The communications system of claim 19, wherein each of the responding nodes includes a counter reset value that to be loaded into the counter that indicates the amount of data to be transmitted by other responding nodes before the control device re-transmits another data block.

21. The communications system of claim 16, wherein each of the responding nodes includes: storage locations associated with addresses; and a data block start address indicating a starting address of the data block in the storage locations.

22. The communications system of claim 21 , wherein each of the responding nodes includes an address translator to translate the data block start address and subsequent addresses into physical addresses of the storage locations from which data are to be retrieved.

23. The communications system of claim 22, wherein the physical addresses are non-contiguous.

24. The communications system of claim 16, wherein one or more of the responding nodes are configurable to transmit their data blocks more than once in response to the predefined command.

25. The communications system of claim 16, wherein the predefined command includes a read command .

26. The communications system of claim 25, wherein each of the responding nodes responds to the read command by transmitting a predefined data block during its transmission period.

27. A control unit coupled to a communications link, comprising: a controller adapted to receive a query and to monitor an amount of data transmitted over the communications link by other control units in response to the query; and a storage element containing a predetermined value indicating a first amount of data, the controller adapted to transmit data after it detects that the first amount of data has been transmitted by other control units.

28. The control unit of claim 27, wherein the controller is adapted to transmit data multiple times in response to the query.

29. The control unit of claim 27, further comprising storage elements and an address translator to convert addresses associated with the query to physical addresses specifying non-contiguous locations in the storage elements.

30. The control unit of claim 29, further comprising a register, wherein the addresses associated with the query includes a starting address stored in the register.