Abstract:
A subsurface electro-hydraulic power unit provided by the present invention permits existing hydraulically actuated well tools to be utilized in situations where control lines extending from the tools to the surface are undesirable or economically prohibitive. In a described embodiment, an electro-hydraulic power unit is in communication with a surface control system. The power unit may be supplied with electrical power from the surface control system, or it may include a power supply, such as batteries. The power unit may respond to a signal transmitted from the surface control system to select from among multiple redundant well tools for actuation thereof.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a well control system utilizing a subsurface electro-hydraulic power unit. 
     It is common practice to control operation of a downhole hydraulically actuated well tool, such as a safety valve, from the earth&#39;s surface using fluid pressure transmitted from the surface to the tool via hydraulic lines, or control lines. Where the tool is within a few thousand feet of the surface, this method is quite satisfactory in practice. However, where the tool is located more than a few thousand feet deep in the well, hydrostatic pressure in the control lines, resistance to fluid flow through the control lines, the cost of running the control lines, the danger of damage to the control lines, the increased number of control line couplings and, therefore, potential leak paths, and other factors make this method unfeasible, or at least undesirable. 
     To solve this problem, hydraulically actuated well tools may be discarded in favor of electrically actuated well tools, or the hydraulically actuated well tools may be redesigned so that some other means is used to actuate the tools. Unfortunately, this solution to the problem requires that substantial costs be incurred in making changes to existing well tools having proven capabilities and reliable operation histories, etc. 
     Therefore, it may be readily seen that it would be quite desirable to provide a method whereby existing hydraulically actuated well tools may be remotely operated from the surface, without requiring use of hydraulic control lines extending between the surface and the tools. 
     SUMMARY OF THE INVENTION 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, a well control system and associated methods are provided which utilize a subsurface electro-hydraulic power unit. The power unit is at least partially controlled by a surface control system in communication therewith. The well control system may operate without the use of any hydraulic control lines extending between the surface control system and the power unit. 
     In one aspect of the present invention, the power unit includes a motor-driven pump which receives electrical power for its operation either from the surface control system via electric lines, or from an internal power source. The pump is connected to one or more well tools using control lines and, thus, no modification of existing control line operated well tools is required for their operation with the power unit. 
     In another aspect of the present invention, the power unit may be configured so that it selectively actuates redundant well tools. In this manner, a second well tool may be actuated by the power unit after a first well tool becomes incapable of performing its function. The power unit may include a valve which is operated in response to a signal transmitted from the surface control system to the power unit to select from among the redundant well tools for actuation thereof. 
     In yet another aspect of the present invention, the power unit may include features which conserve electrical power consumed by the power unit. These features may be particularly desirable where the power unit includes a power supply, such as batteries. In one such feature, the power unit may include a pressure transducer which is used to monitor the pressure of the pump output, thereby enabling the pump to be shut off when the pressure is in a predetermined acceptable range for actuating a certain well tool. In another such feature, a position sensor may be utilized in the well tool to monitor the position of a member of the tool, thereby enabling the pump to be shut off when the member is in a predetermined acceptable position or range of positions. 
     In still another aspect of the present invention, the power unit may include a reservoir for fluid pumped by the pump. A fluid quality sensor may monitor the quality of the fluid in the reservoir. An indication of fluid quality may be transmitted by the power unit to the surface control system. 
     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a first well control system embodying principles of the present invention; 
     FIG. 2 is a schematic view of a second well control system embodying principles of the present invention; 
     FIG. 3 is a schematic view of a communication and power transmission method which may be used in the first well control system; 
     FIG. 4 is a schematic diagram of a downhole electro-hydraulic power unit which may be used in the first and second well control systems; 
     FIG. 5 is a partially cross-sectional view of an optional redundant well tool control method which may be used in the first and second well control systems; and 
     FIG. 6 is a flow chart of a pressure monitoring method which may be used in the power unit. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIG. 1 is a well control system  10  which embodies principles of the present invention. In the following description of the well control system  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention. 
     The well control system  10  is described herein as being utilized to control actuation of a hydraulically operated well tool  12 , representatively a safety valve, in a manner that does not require running control lines from the surface to the tool, and that does not require modifications to the tool for such actuation. However, it is to be clearly understood that tools other than safety valves, such as sliding sleeve-type valves and tools other than valves, may be actuated by the well control system, and control lines or other hydraulic lines may be utilized in the system  10 , without departing from the principles of the present invention. 
     The well control system  10  includes a surface control system  14  and a downhole electro-hydraulic power unit  16 . The surface control system  14  is in communication with the power unit  16  by means of one or more electrical lines  18  extending therebetween. The power unit  16  may also be supplied with electrical power from the surface control system  14  via the lines  18 , as described in more detail below. Alternatively, the power unit  16  may include a separate power supply  20 , such as one or more batteries (see FIG.  4 ). 
     Note that the power unit  16  and the safety valve  12  are both interconnected in a tubular string  22  positioned in a well. In this manner, the power unit  16  and the safety valve  12  are in relatively close proximity to each other and one or more hydraulic lines  24  extending therebetween are relatively short, compared to the distance between the safety valve and the earth&#39;s surface. Thus, the problems associated with running, maintaining and utilizing very long hydraulic control lines are eliminated. 
     In an alternate embodiment, communication between the surface control system  14  and the power unit  16  may be accomplished by means other than electrical lines  18 , as representatively illustrated in FIG. 2. A well control system  30  depicted in FIG. 2 utilizes an acoustic transmitter/receiver  32  at the surface connected to, or incorporated in, the surface control system  14 . A separate acoustic transmitter/receiver  34  is interconnected in the tubing string  22  and is connected to, or incorporated in, the power unit  16 . Such acoustic transmitter/receivers  32 ,  34  may not necessarily both transmit and receive acoustic signals, since, for example, the one at the surface may only transmit signals and the one in the tubing string may only receive such signals, but it is preferred that two-way communication be used with the transmitter/receivers. 
     The acoustic transmitter/receivers  32 ,  34  may be any of those acoustic transmitters and/or receivers well known to those skilled in the art of remote data transmission in wells. Such acoustic transmitters and/or receivers communicate by transmission and reception of pressure pulses or acoustic waves including data-carrying signals. 
     Turning now to FIG. 3, the electrical lines  18  utilized in the method  10  are schematically shown extending from the surface control system  14 . The representatively illustrated method of transmitting power and signals via the lines  18  is to be clearly understood as merely an example of the wide variety of such methods which may be used in the well control system  10 . Many other power and signal transmission methods may be utilized, without departing from the principles of the present invention. 
     The lines  18  include a shield  26  connected to ground and two conductors  36 ,  38 . The conductors  36 ,  38  are inductively coupled to the surface control system  14  at the surface, and to the power unit  16  downhole (see FIG.  4 ). This configuration is known as a phantom circuit and enables provision of signals superimposed on power transmitted via the lines  18 . 
     Referring additionally now to FIG. 4, a schematic of the downhole power unit  16  interconnected to the safety valve  12  and another safety valve  40  is representatively illustrated. The safety valve  40  is redundant to the safety valve  12 , since it performs the same function. In actual practice, the safety valve  40  would not be utilized until the safety valve  12  becomes incapable of performing its function, for example, when the safety valve  12  can no longer properly shut off flow through the tubing string  22 . 
     The safety valve  40  is indicated in FIG. 4 by the abbreviation “WSV”, since it preferably includes a wireline conveyed safety valve  42  installed in a nipple  44  (see FIG. 5) after the safety valve  12 , which is preferably a tubing conveyed safety valve, becomes incapable of performing its function. The nipple  44  is interconnected in the tubing string  22  along with the safety valve  12  when the tubing string is installed in the well. Alternatively, the safety valve  40  may be what is known to those skilled in the art as an insert valve, that is, it is inserted into the safety valve  12  when it becomes incapable of performing its function, as a remedial measure. However, it is to be clearly understood that the safety valves  12 ,  40  may be any type of safety valves, or any type of hydraulically actuated tools, may be different types of tools and not redundant, and may be conveyed into the well in any manner, without departing from the principles of the present invention. 
     The power unit  16  is connected to the lines  18  as described above for communication with the surface control system  14  and for provision of electrical power if the power unit  16  does not include the internal power supply  20 . The lines  18  are connected to a power/communications unit  50 . The power/communications unit  50  is connected to a data acquisition and control unit  52 . 
     The data acquisition and control unit  52  is connected to a conventional motor control  54 , which controls operation of a motor-driven pump  56 . The pump  56  receives fluid from a reservoir  58  and pumps it at elevated pressure via an output line  60  to a solenoid valve  62 . A return line  64  returns the fluid to the reservoir  5 &amp; A check valve  66  ensures that pressure in the line  60  does not bleed off back through the pump  56 , thus helping to maintain elevated pressure in the line  60  downstream of the check valve. A pressure transducer or other pressure sensor  68  monitors pressure in the line  60  downstream of the check valve  66 , and the output of the transducer is input to the data acquisition and control unit  52 . 
     In the depicted power unit  16 , the data acquisition and control unit  52  is programmed to maintain the pressure in the line  60  as indicated by the transducer  68  within an acceptable predetermined range for operation of the safety valve  12  or other tool connected thereto. For example, the data acquisition and control unit  52  may be programmed with a maximum pressure or upper pressure limit and a minimum pressure or lower pressure limit, so that the pump  56  is turned on when the pressure in the line  60  as indicated by the transducer  68  falls to the minimum pressure, and the pump is turned off when the pressure rises to the maximum pressure. Alternatively, such control of the pump operation may be implemented in the surface control system  14 , with the pressure indications from the transducer  68  being transmitted to the surface via the lines  18 . 
     It will be readily appreciated that this method of controlling operation of the pump  56  results in a significant reduction in power consumed by the pump  56 , as compared to using a conventional pressure regulator to control the pump&#39;s output pressure. This reduction in power consumption is highly advantageous where the downhole power supply  20  is used to provide power to the pump  56 . 
     One or both of the safety valves  12 ,  40  may have a position sensor  70 , such as a hall effect device, proximity sensor, linear variable displacement transducer, etc., therein for monitoring the position of a member of the safety valve. For example, the position sensor  70  may indicate the position of an opening prong of the safety valve  12  and/or  40 , to determine if the safety valve is fully open. The positioning and displacement of an opening prong or flow tube to open and close a safety valve is described in U.S. Pat. No. 5,465,786, the disclosure of which is incorporated herein by this reference. 
     The position sensor  70  is connected to the data acquisition and control unit  52 . If it is desired to change the position of the member of the valve  12  and/or  40  that the position sensor  70  monitors, the data acquisition and control unit  52  will cause the pump  56  to deliver pressurized fluid to the line  60 , and will actuate the solenoid valve  62  to effect the change in position. 
     In the representatively depicted power unit  16 , the data acquisition and control unit  52  is programmed to maintain the position of the member as indicated by the sensor  70  in a predetermined position. The predetermined position may be a range of displacement relative to a reference point. For example, the data acquisition and control unit  52  may be programmed with a maximum displacement and a minimum displacement, so that the pump  56  is turned on when the position of the member is outside the displacement range, and the pump is turned off when the member is within the displacement range. Turning the pump  56  off when the valve member is in the predetermined position conserves power, which is particularly desirable when the power supply  20  is used to provide power to the power unit  16 . Alternatively, such control of the pump operation may be implemented in the surface control system  14 , with the position indications from the sensor  70  being transmitted to the surface via the lines  18 . 
     Referring additionally now to FIG. 6, a flow chart is depicted of a method  80  whereby the data acquisition and control unit  52  may be programmed to maintain pressure in the line  60  between the upper and lower pressure limits. It will be readily appreciated by one skilled in the art that a similar method may be used with the position sensor  70  to maintain the position of the member of the safety valve  12  and/or  40  within an acceptable predetermined range. 
     The method begins at the start step  82 . In step  84 , a decision is made whether to open the valve. As with most conventional safety valves, if sufficient pressure is not applied to an appropriate hydraulic control line, the valve will close, due to a biasing member, such as a spring, urging the valve to close. Thus, pressure need only be applied to the line  60  when it is desired to open the valve, or to maintain the valve in its open position. The decision in step  84  whether to open the valve may be made internally in the power unit  16 , or it may be the result of an instruction transmitted to the power unit from the surface control system  14 . 
     If the decision in step  84  is to close the valve, the program goes to step  86 . Step  86  results in power being removed from the solenoid valve  62  by the data acquisition and control unit  52 . Step  86  also follows step  78  if no power is supplied to the power unit  16 . When no power is supplied to the solenoid valve  62 , it connects the output line  60  directly to the return line  64 . Thus, even if pressure exists in the line  60  when the decision is made to close the valve, this pressure will be relieved when no power is supplied to the solenoid valve  62  and the valve will be permitted to close. 
     If the decision in step  84  is to open the valve, the program goes to step  88  in which the solenoid valve  62  is energized. This connects the output line  60  to the line  24 . Pressure in the line  60  is now delivered to the valve  12 . Note that the pressure in line  60  could alternatively be delivered to the valve  40  via a line  90  if another solenoid valve  92  is actuated by the data acquisition and control unit  52 , as described in more detail below. 
     In step  94 , the upper and lower pressure limits are set. For example, it may be known that a certain pressure is needed to open the valve, and that a certain greater pressure may cause damage to the valve. In that case, the lower limit may be set somewhat above the opening pressure, and the upper limit may be set somewhat below the damaging pressure. The pressure limits may be preprogrammed in the data acquisition and control unit  52  prior to installing the power unit  16 , the pressure limits may be transmitted to the power unit by the surface control system  14  after the power unit is installed, or any other method may be used for setting the pressure limits. 
     If the pressure in the line  60  as indicated by the pressure transducer  68  is below the lower limit, as it should be upon initial opening of the valve, the pump  56  is started in step  96 . In step  98 , if the upper pressure limit is not yet reached, the pump  56  remains operating. When, however, the upper pressure limit is reached, the pump  56  is stopped in step  100 . 
     At this point, due to temperature fluctuations, leakage, etc., the pressure in the line  60  as indicated by the transducer  68  may decrease. The pressure indication from the transducer  68  is monitored by the data acquisition and control unit  52  in step  102 , and if the lower pressure limit is reached, the pump  56  is again started in step  96 . In this manner, the pressure in the line  60  as indicated by the transducer  68  is maintained between the upper and lower pressure limits by the data acquisition and control unit  52 . Alternatively, some or all of these control functions may be performed by the surface control system  14 , with the data acquisition and control unit  52  merely functioning to receive data from the sensors  68 ,  70  and carry out instructions transmitted from the surface control system. 
     It will be readily appreciated by one skilled in the art that the method  80  may alternatively be used to control the position of a valve member, such as an opening prong of a conventional safety valve or a sleeve of a sliding sleeve valve, as indicated by the position sensor  70 . For example, the pump  56  may be operated when the member is outside of a predetermined position, as defined by upper and lower displacement limits, and the pump may be deactivated when the member is in the predetermined position. In that case, the upper and lower displacement limits would be substituted for the upper and lower pressure limits shown in FIG.  6 . Thus, the method  80  may be used to control a variety of aspects of operation of well tools. 
     Referring again to FIG. 4, the reservoir  58  has a fluid quality sensor or oil sensor  106  therein. The sensor  106  may be a conductivity or a dielectric sensor, or another type of sensor. The sensor  106  is utilized in the power unit  16  to detect the quality of the fluid in the reservoir  58 , for example, to determine whether well fluids have invaded the reservoir fluid. The reservoir fluid may be oil and the sensor  106  may be capable of detecting whether water has become mixed with the oil or is otherwise present in the reservoir. The sensor  106  is connected to the data acquisition and control unit  52 , and the indications of fluid quality from the sensor may be transmitted to the surface control system  14  via the power/communications unit  50 . 
     A pressure/temperature compensation device  108  is connected to the reservoir  58 . The device  108  may be a floating piston which acts to increase or decrease the volume of the reservoir  58  as the reservoir fluid expands or compresses due to a change in temperature or pressure, etc. Preferably, the device  108  acts to maintain the pressure of the fluid in the reservoir at the hydrostatic pressure in the well. 
     The solenoid valve  92  is used in the power unit  16  to control to which of the valves  12 ,  40  fluid pressure is delivered from the line  60 . Of course, if the solenoid valve  62  is not actuated by the data acquisition and control unit  52 , neither of the lines  24 ,  90  may be connected to the line  60 . Thus, to deliver pressurized fluid from the line  60  to the valve  12 , the solenoid valve  62  is actuated and the solenoid valve  92  is not actuated, thereby connecting the line  60  to the line  24 . To deliver pressurized fluid from the line  60  to the valve  40 , the solenoid valve  62  is actuated and the solenoid valve  92  is actuated, thereby connecting the line  60  to the line  90 . Note that, to deliver pressurized fluid to either of the valves  12 ,  40 , the solenoid valve  62  must be actuated and, therefore, a fail-safe condition is presented, since neither valve may be opened if electrical power to the power/communications unit  50  is interrupted. 
     The description above of the operation of the solenoid valve  92  to select from among redundant well tools  12 ,  40  may be further illustrated by referring to FIG.  5 . Recall that the tubing string  22  as illustrated in FIG. 5 includes a separate nipple  44  for landing therein of a safety valve  42 . When the tubing string  22  is initially installed, the safety valve  42  is not present in the nipple  44 . Instead, the safety valve  12  initially performs the function of preventing flow through the tubing string  22  if desired. 
     At this point, the valve  12  is opened by actuating the solenoid valve  62  and delivering pressurized fluid from the line  60  to the line  24  as described above, without actuating the solenoid valve  92 . To close the valve  12 , the solenoid valve  62  is deactivated, thereby connecting the line  24  to the return line  64  and relieving pressure in the line  24 . 
     If the valve  12  should become incapable of performing its function, the valve  42  may be installed in the nipple  44  and operated by actuating the solenoid valve  92 . With the solenoid valve  92  actuated, operation of the valve  40  is the same as described above for the valve  12 . 
     The power unit  16  has been described above as it is used to operate the redundant valves  12 ,  40 . However, it is to be clearly understood that the power unit  16  may be otherwise utilized, without departing from the principles of the present invention. For example, only one valve  12  could be operated by the power unit  16 . In that case, the solenoid valve  92  could be eliminated from the power unit  16 . As another example, the lines  24 ,  90  would be used to operate another well tool, such as a sliding sleeve-type valve. In that case, pressurized fluid could be applied to the line  90  to bias a sleeve of the sliding sleeve valve to an open position, and pressurized fluid could be applied to the line  24  to bias the sleeve to a closed position The position sensor  70  could be used to monitor the position of the sleeve. Thus, principles of the present invention may be utilized to control operation of a wide variety of well tools. 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.