Abstract:
A system for communicating with downhole tools and devices is disclosed. The system includes multiple communication devices which, in combination, permit operators at the surface to operate downhole tools and to receive feedback regarding the state of the tools.

Description:
RELATED APPLICATIONS 
     This application is a continuation of PCT/NO2007/000107, filed Mar. 19, 2007, which was published in English and designated the U.S., and claims priority to NO 20061275 filed Mar. 20, 2006, each of which are included herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field 
     The field relates to a system and a method for remote activation of downhole tools and devices used in association with wells for the production of hydrocarbons. 
     2. Description of Related Technology 
     Oil- and gas producing wells are designed in a range of different ways, depending on factors such as production characteristics, safety, installation issues and requirements to downhole monitoring and control. Common well components include production tubing, packers, valves, monitoring devices and control devices. 
     An extremely important consideration for all design and operations is to maintain a minimum number of barriers (e.g. 2) between the high-pressurised reservoir fluids and the open environment at the surface of the earth. Packers and valves are examples of commonly used mechanical barriers. Other barriers can be drilling mud and completion fluid which create a hydrostatic pressure large enough to overcome the reservoir pressure, hence preventing reservoir fluids from being produced. 
     Following the drilling stage; the installation of the production tubular, including a selection of the above described components and the wellhead is referred to as completing the well. During completion, temporary barriers are used to ensure that barrier requirements are adhered to during this intermediate stage. Such temporary barriers could be, for example, intervention plugs and/or disappearing plugs mounted in the lower end of the production tubing or the higher end of the well&#39;s liner. 
     Intervention plugs are typically installed and retrieved with well service operations such as wireline and coil tubing. Disappearing plugs are temporary barrier devices that are operated with pressure cycling from surface, i.e. surface pressure cycles are applied on the fluid column of the well to operate pistons located in the downhole device (disappearing plug). After a certain amount of cycles, the disappearing plug opens (i.e. “disappears”), hence the barrier is removed according to the well completion program. 
     Evolution of oil wells has included well designs such as multi lateral wells and side-tracks. A multilateral well is a well with several “branches” in the form of drilled bores that branch from the main bore. Multilateral wells allow a large reservoir area to be drained with one primary bore from the surface. A side track well is typically associated with an older production well that is used as the foundation for the drilling of one or more new bores. Hence, only the bottom section of the new producing interval needs to be drilled and time and costs are saved. 
     To sidetrack a well, the following operational method may be used: 
     One starts by installing a deep-set barrier in the wellbore, above the top of the old producing interval and below the kick-off point for the new branch to be drilled. 
     A whipstock is installed—this is a wedge shaped tool utilised to force the drill bit into the wall of the wellbore and into the formation. 
     The branch is drilled. 
     The branch is completed with the preferred selection of completion components. 
     The temporary barrier in the original bore is removed, if possible. 
     The well is put on production, producing from both the new and the old bore. 
     The new well designs (i.e. branches) have introduced a new challenge in the form of inaccessible areas of the well. Traditional operation of the above described temporary barrier systems may no longer be possible. Well intervention strings are normally not operated below junctions of branch wells, as the risk of getting stuck or causing other types of damage is considered too high. Also, in a branch well, one does not normally manage to seal off all rock faces, hence pressure cycling to operate traditional disappearing plugs might not be possible as the exposed rock may prevent the generation of pressure cycles of the required amplitude. Accordingly, the internal piston (or bellows or other similar mechanism) arrangements of the disappearing plugs cannot be operated. 
     In addition, certain specific completion methodologies for the new branch of a sidetrack well, for example if the branch&#39;s liner top is attached to the original well bore, or the whipstock being left in the well after sidetracking, will make the old producing interval totally non-accessible. Again, this will represent challenges with respect to the removal of traditional, temporary deep-set barriers. 
     SUMMARY OF CERTAIN INVENTIVE ASPECTS 
     One aspect provides a novel and alternative system for remote activation of downhole tools and devices associated with wells for the production of hydrocarbons. One embodiment will enable operation, activation and/or removal of components located in inaccessible areas of wells such as branch wells and sidetracks. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in more detail by means of the accompanying figures. 
         FIGS. 1-4  illustrates various embodiments of the invention. 
         FIGS. 5-11  illustrates possible ways of designing the transmitter and/or the receiver in more detail. 
         FIG. 12  illustrates one possible way of designing the receiver electronic package. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One method for activation/removal of temporary barriers in sidetrack wells, is to utilise deep set barriers in the form of glass plugs equipped with a timer that detonates an explosive charge and removes the plug after a predetermined time. In this way, the barrier element acts as an autonomous device operating according to its own pre-programmed logic. Because it is autonomous, the system could be installed in inaccessible regions of a well and still work satisfactorily. The drawback with this method is that the memory has to be pre-programmed at the surface, prior to installing the deep-set barrier in the well. Because of that, the following has to be taken into consideration: The deep-set barrier is not removed before the sidetracking operation is finished. Hence, a margin has to be included in the programming. For example, if a sidetrack operation is estimated to take 20 days, the timer arrangement might be programmed to remove the deep-set barrier after 40 or 60 days. Hence, one risks losing a significant amount of production time because the original well bore remains closed for a long time after the side track operation is completed. Also, if the drilling and completion is conducted from a floating drilling rig, the rig will normally be moved off location once the completion is finished. The delay in removing the last barrier means, that should the timer method fail to operate, there will not be any rig on the site to perform any remedial work. Hence, substantial time and production might be lost awaiting a new rig to be available for the removal of the last barrier. 
     Pressure cycling can be used to remotely activate disappearing plugs and other well components from surface. The principle involves using a pump on the surface to pressurize the well (completion) fluid repeatedly according to certain protocols. The pressure cycles are transmitted across the fluid column and an equal increase in pressure downhole operates piston- bellows- or similar arrangements which again are linked to an activation mechanism. Such systems use a minimum amount of differential pressure across the piston-, bellows- or similar arrangement to operate the mechanism. For many new well scenarios, including sidetracks and multilaterals, parts of the wells rock face could be exposed. Hence, when trying to cycle pressure, fluid escaping into the exposed rock could prevent the required downhole pressure increases to take place. Hence, the method becomes unreliable and non-feasible for some types of well scenarios. 
     There also exists numerous ways to use wireless signalling to remotely activate downhole components. U.S. Pat. No. 6,384,738 B1 describes the use of a surface air-gun system to communicate through a partly compressible fluid column. In a somewhat similar manner, the “EDGE” system (trademark of Baker Hughes) uses a surface signal generator to inject pulses of chosen frequency into the wellbore. With regards to this system, a downhole tool, for instance a packer, is equipped with a signal receiver which again interfaces towards a controller system. When the surface-transmitted signal is received downhole, it is interpreted and used to generate the action of intent, for example the setting of the packer. 
     When sidetracking a well, the section between the temporary barrier and the kick off point for the branch normally becomes filled with cuttings from the drilling process plus settling particles (barite) from the drilling mud. This will potentially have a very negative effect on wireless acoustic signals transmitted in the fluid column. In addition, certain completion methods may create geometrical patterns of the continuous liquid column that could cause additional damping and scattering effects. Examples of this are perforated whipstocks that will contain only small conduits and a geometrical pattern of flow as well as acoustic waves that will differ substantially from the general tubing profile. 
     The airgun system related to U.S. Pat. No. 6,384,738 B1 intended to work with a compressible fluid in the top of the well column and an incompressible bottom section, could be non-suitable for the activation of a deep set barrier after a sidetrack drilling operation, as the signal will get dampened along the wellbore, and the additional, last part of the path comprising cuttings, barite and irregular geometry may dampen the signal significantly, below a detectable level for the receiver. The same applies for the EDGE system (trademark of Baker Hughes). 
     Also, when activating a component in a sidetrack or multilateral well, with exposed rock faces, it can be very difficult to verify that the desired downhole operation actually has taken place by monitoring surface parameters such as pressure or flow. None of the above described methods are equipped with relevant monitoring features enabling feedback to the surface on the performance of the downhole operation. A more accurate and reliable feedback system is required. 
     Certain embodiments include bringing a wireless signal transmitter into the well, to a close proximity of the receiver, in order to overcome excessive dampening effects related to cuttings/barite fill and complex fluid column geometries. Also, some embodiments include a reliable feedback system to verify operational success. 
     In some embodiments, a signal transmitter and a signal receiver system, are located in a position higher and lower in the well, respectively. The receiver is associated with a downhole device of interest, for example a temporary barrier element. Another embodiment includes a signal transmitter and a signal receiver system, located in a position lower and higher in the well, respectively. Another embodiment includes a combination of signal transmitter(s) and receiver(s) at two or several locations in the well. 
     In some embodiments, the transmitter is in the form of a well intervention tool that is run into the well by means of a well service technique such as wireline or coil tubing. This enables the transmitter to be brought to a close proximity to the downhole receiver. The transmitter can be built as a stand-alone module or interface towards a 3 rd  party well intervention tool, such as a wireline tractor. 
     In one embodiment, the transmitter is located at the surface, on or in the proximity of the wellhead. 
     In yet another embodiment, the transmitter is associated with a downhole device, to transmit downhole information to a signal receiver placed higher in the well. This could be a downhole data acquisition device that, on a frequent basis, uploads data to a receiver located at a higher point in the well, either on the surface or in the form of a downhole tool, lowered into the wellbore to a close proximity to the transmitter. The latter case would entail a larger bandwidth of the data transfer. 
     In some embodiments, both the modules (located higher and lower in the well) can transmit and receive signals, i.e. function as transceivers. The upper and lower transceiver represent a two way communication system that for example can be used to remotely activate a downhole device whereupon information is sent from the lower system to the higher system to verify the execution of a desired operation. 
     In some embodiments, the receiver is associated with an activation system, so that the main receiver function is to read and interpret the activation signal from the transmitter, whereupon a subsequent activation command is sent from the receiver to the activation system in order to do work on the downhole component, for example the removal of a deep-set barrier after a sidetrack operation is completed. In one embodiment, the activation system is part of the overall system. In another embodiment, the receiver is built into a module of its own that interfaces towards a 3 rd  party activation system. 
     Common applications would be the activation of downhole well components that are located in such position that they are non-accessible and/or non-feasible for well intervention toolstrings as well as existing techniques for remote activation. 
       FIG. 1  illustrates an overall system description for an embodiment of a plug, a valve or other types of downhole devices. The downhole device is associated with a signal receiver  103  and an activation system  104 . A wireline  105  and associated toolstring  106  is used to deploy a signal transmitter  107  into the well  101 . The set of dotted lines shows that the well comprises a well section that is available for intervention  108  and a well section that is non-available for intervention  109 . The toolstring  106  may be equipped with a wellbore anchor  110 . The anchor  110  may be used to assure stability of the transmitter  107  during operation in order to impose an optimum signal into the primary signalling medium (the well fluid) and/or a secondary/complementary signalling medium (the steel tubing of the well  101 ). The transmitter  107  may be designed for producing a signal with sufficient strength to overcome obstacles related to solids and/or liquids as well as well geometries with poor acoustic properties 
       FIG. 2  illustrates a system of another embodiment. A wellbore  101  includes a downhole device  102 . For this embodiment, a signal transmitter  107  is placed in or near a wellhead  205  in connection with the well  101 . 
       FIG. 3  illustrates yet another embodiment. A wellbore  101  includes a downhole device  102 . The downhole device is associated with a signal receiver  103 , an activation system  104 , and a signal transmitter  301 . A wireline  105  and associated toolstring  106  is used to deploy a tool comprising signal transmitter  107  and signal receiver  302  into the well  101 . This configuration enables two way communication which, as an example, will enable a confirmation-of-execution signal to be sent from the downhole transmitter  301  to be received by the receiver  302  after activation of the downhole device  102 . In one embodiment, the receiver  302  may be associated with sensor systems monitoring parameters such as wellbore noise patterns resulting from the activation of the downhole device  102 . 
       FIG. 4  illustrates yet another embodiment. A wellbore  101  includes a downhole device  102 . The downhole device  102  is associated with a signal receiver  103 , an activation system  104 , and a signal transmitter  301 . A signal transmitter  107  and a signal receiver  302  are placed in or near a wellhead  205  in connection with the well  101 . 
       FIG. 5  illustrates a transmitter  107 . The transmitter  107  comprises an actuator  501  that is attached to a flexible membrane  502  filled with a fluid  503 . Also, the transmitter  107  in this example comprises an electronic module  504  and an interface toward a 3 rd  party wireline tool  505 . Through the electrical cable  105  of  FIG. 1 , a command is transmitted from the surface to the electronic module  504 . Further, the command is transferred to the actuator  501 , which is put into oscillations. Typically, the actuator  501  is a sonic actuator made of piezo-electric wafers or a magnetostrictive material such as Terfenol-D. When the actuator  501  is put into oscillations, these oscillations are transferred to the well fluid by the membrane  502 . The membrane fluid  503  prevents the membrane from collapsing in the high pressurised well environment. Also, an anchor  110  (shown in  FIG. 1 ) might be used to optimize the process of transferring the signal into the primary signalling medium (the well fluid) as well as enable the possibility for using a secondary, supplementary signalling medium (the steel tubing). The basic principles of  FIG. 5  may also apply for the transmitter  301  of  FIGS. 3 and 4 . 
       FIG. 6  illustrates an embodiment of receiver  103  of  FIG. 1 . Receiver  103  may be associated with a transmitter  107  as illustrated in  FIG. 5 . The receiver  103  includes a vibration sensor  601  that is fixed to a flexible membrane  602  filled with a fluid  603 . Vibration sensor  601  may be, for example, a piezoelectric disc, an accelerometer, or a magnetostrictive material. The receiver  103  also comprises an electronic section  604 , a battery section  605  and an activation module  606 . A signal from the transmitter  107  of  FIG. 5  is transmitted through the well fluid and/or the walls of the completion tubing in the form of acoustic waves. Typically, for the operations of interest, the well  101  is filled with a stagnant completion fluid, for example brine. The signal makes the membrane  602  of the receiver  103  oscillate, and this oscillation is registered by the vibration sensor  601 . The sensor is read by the electronic module  604  where the information/signal is decoded. If the code overlaps with the activation code for the relevant downhole device of interest, an activation signal is transferred to the activation module  606 , whereupon tool activation is executed. As the receiver  103  is located in a section of the well where there is no transfer of power from surface, the receiver  103  is powered by the batteries of the battery module  605 . The basic principles of  FIG. 6  may also apply for the receiver  302  of  FIGS. 3 and 4 . 
       FIG. 7  illustrates another receiver  103  of  FIG. 1 . For this embodiment, the receiver  103  comprises a vibration sensor  601  that is fixed to the body  701  of receiver  103 . The basic principles of  FIG. 7  may also apply for the receiver  302  of  FIGS. 3 and 4 . 
       FIG. 8  illustrates an embodiment of the transmitter  107  of  FIG. 1  in more detail. The transmitter body comprises a connector  801 , a housing  802 , and a flexible membrane  502 . The connector  801  provides a mechanical and electrical connection towards a standard wireline tool string (ref  106  of  FIG. 1 ). An electrical feedthrough  804  provides an electrical connection to the wireline toolstring and from thereon to operator panels on the surface. The tool comprises an electronic circuit board  805 , a connection flange  806 , an actuator  501 , and a coupler device  807  to compensate for deflections of the membrane  502  as the tool is lowered into the highly pressurised well regime. Operator commands are transferred from surface via the wireline cable (ref  105  of  FIG. 1 ) to the electronic circuit board  805 . The commands are processed in the electronics circuit board  805 , and a signal is sent to the actuator  501  which is put into oscillations as defined by said signal. One end of the actuator  501  is fixed to the tool housing  802  via a connection flange  806  within the tool body. The oscillations are transferred to the flexible membrane  502  via the coupler  807 . 
     The coupler  807  may be any kind of arrangement that allows for pressure imposed deflection of the membrane  502  without creating excessive stresses in the actuator  501  and still being able to transfer oscillations from the actuator  501  to the membrane  502 . 
     In one embodiment, the coupler  807  is a hydraulic device, which comprises a piston  808  with a micro orifice  809 , and a cylinder  810  filled with hydraulic oil  811 . The oscillations are transferred from the actuator  501  into the piston  808 , which will put oscillating forces into the hydraulic oil  811 , which in turn will transfer said oscillations into the cylinder body  810 , which in turn will transfer the oscillations into the flexible membrane  502 , which in turn will transfer said oscillations into the wellbore fluid and/or the completion components, which in turn will transfer said oscillations to the signal receiver (ref  103  of  FIG. 1 ). 
     The micro orifice  809  is made sufficiently small to not allow for rapid fluid flow, such that the oscillating forces will be transferred to the membrane  502  according to the orifice  809 . By the same token, the micro orifice  809  will allow for sufficient fluid flow to match the relatively slow deflection movement of the membrane  502  as a function of submerging the tool into the well (i.e. increasing the surrounding pressure). Hence, the micro orifice  809  functions as a pressure compensator for the system as the transmitter  107  is placed into a well. This enables the actuator  501  to function under atmospheric conditions regardless of exterior well pressure, which is advantageous, as no hydrostatic pressure related stresses, direct as well as indirect, will be imposed onto the actuator material. As exterior well pressure increases, the micro orifice  809  will allow oil to be transferred across the piston such that exterior pressure will not apply forces to the piston  808  and hence to the actuator  501 . 
     A sensor  812  attached to the housing  802  is included to monitor the sonic/vibration in the well or other relevant parameters. The information sensed is transferred to the electronics circuit board  805  where it is processed and transferred to surface via the wireline cable  105 . The information will supply the surface operator with information related to both transmitter operation and other parameters (for instance vibration or noise pattern) resulting from the activation of a said downhole device. The sensor  812  forms a part of the receiver  302  described in  FIG. 3 . 
       FIG. 9  illustrates an alternative embodiment of the coupler  807 . A shaft  9001 , is attached to the flexible membrane  502 , is mounted to slide along its main axis inside the bore of an engagement sub  9002 . During the part of an operation where the transmitter  107  is lowered into the well  101 , the shaft  9001  is free to move longitudinally inside the bore of the engagement sub  9002 . As the external pressure increases and the flexible membrane deflects due to this, the shaft  9001  slides further into the bore of the engagement sub  9002 . Upon the time of signalling, an engagement system  9003  is engaged in order to lock the shaft  9001  inside the engagement sub  9002 . A solid connection is then formed between the actuator  501  and the flexible membrane  502 . In order to engage the engagement system  9003 , various methods may be utilised. One example of such is a motor driven engagement system powered by one or more electric line(s)  9004  that comes from the system electronics. In one embodiment, the engagement sub  9002  also pre-tensions the membrane  502  with respect to the actuator  501  in order to generate prepare the oscillation system. 
       FIG. 10  illustrates one embodiment of the receiver  103  of  FIG. 1  in more detail. This receiver  103  may be associated with a transmitter  107  as illustrated in  FIG. 8 . The receiver  103  includes a vibration sensor  601 , an electronic circuit board  604 , and a battery pack  605 , which are all placed inside the wall of a tubing  901 . The tubing  901  may have the same physical shape as other completion and/or intervention equipment in the well  101 , such that the whole system can be integrated into a downhole assembly. Such downhole assembly can be any downhole completion and/or intervention device equipped with an activation system. A unique signal is transferred via the wellbore fluid and/or completion components, as explained for  FIG. 5  above. This signal is picked up by the vibration sensor  601  and processed by the electronic circuit board  604 . The electronic circuit board will transmit another signal to the activation module  606  of the downhole device  102  whereupon the desired operation is executed. The activation module  606  can be integrated into the wall of tubing  901  or can be built into a 3 rd  party supplied device. 
       FIG. 11  illustrates another receiver  103  of  FIG. 1  in more detail. Receiver  103  of  FIG. 11  is in general the same as that presented in  FIG. 9 , but here all system components are placed inside a tube  1001  of a relatively small outer diameter. This tubing  1001  may be made to be attached to a downhole device  102 . 
       FIG. 12  illustrates one embodiment of the electronics module  604  of receiver  103  of  FIGS. 1 ,  10  and  11 . The electronics module  604  may be associated with an activation module  606  as described in  FIG. 6 . A signal transmitted from the signal transmitter  107  of  FIG. 8  through the wellbore fluid and/or the completion components impart stresses and tension onto the vibration sensor  601  resulting in an electrical signal. The electrical signal is amplified by the pre amp  1101 , and the variable gain amp  1102 , and converted into a digital signal by the signal converter  1103 . 
     The digital signal from the signal converter  1103  is processed by the digital signal processor  1105 , and if the received signal is according to a preprogrammed protocol, the digital signal processor  1105  sends an activation signal to activate the trigger mechanism  1106 , which in turn allows the activation signal to be transmitted to the activation system of the downhole device. The trigger mechanism  1106  includes a safety function which provides a circuit breaker point (for instance an inductive coupling) between the receiver electronics module  604  and any activation system  606  to be activated. The circuit breaker prevents accidental activation of the downhole device due to stray currents or other accidental bypasses of the activation system. In one embodiment, the signal is defined by FSK (Frequency Shift Key) coding. This eliminates possibilities for the wireless signal to be produced by noise that could be present in the well  101  (for instance during drilling), leading to accidental, premature activation of the downhole device. 
     The complete system may, as default, be kept in an idle mode to save energy (battery) while awaiting the activation signal. The full operation of the circuitry may be initiated by recognition of a predetermined signal registered by the wake up circuit  1104  (i.e. the signalling operation may be initiated by a wake up signal). 
     While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others.