OA12214A - Downhole wireless two-way telemetry system. - Google Patents

Abstract

A petroleum well having a wireless power and data communication system is provided. The well uses the tubing and/or casing to communicate with and power a plurality of devices, such as sensors and controllable valves. An electrically isolating portion of a tubing hanger at the surface of the well and a ferromagnetic choke downhole may electrically isolate the tubing from the casing and provide a communications path. A plurality of modems positioned downhole along the tubing string communicate sensor information to a modem and a computer located at the surface of the well. Based on an analysis of the sensor information received by the computer, instructions can be communicated along the tubing string to the controllable valves to adjust the flow rate of lift gas passing through the valves.

Description

1 012214

BACKGROUND OF THE INVENTION 1. Field of the Invention

The présent invention relates generally to acommunication System for a petroleum or gas well havingdownhole devices for monitoring and adjusting productionof the well, and in particular, to a communication systemhaving a two-way telemetry backbone with redundantrepeaters, sensors, and controllable valves. 2. Description of Related Art

Gas-lift wells hâve been in use since the 1800's andhâve proven particularly useful in increasing efficientrates of oil production where the réservoir natural liftis insufficient (see Brown, Connolizo and Robertson, WestTexas Oil Lifting Short Course and H.W. Winkler,Misunderstood or Overlooked Gas-lift Design and--EquipnientConsidérations, 3FE, p. 351 (1994)). Typically, in a gas-lift oil well, natural gas produced in the oil field iscompressed and injected in an annular space between thecasing and tubing and is directed from the casing intothe tubing to provide a "lift" to the tubing fluid columnfor production of oil out of the tubing. Although thetubing can be used for the injection of the lift-gas andthe annular space used to produce the oil, this is rarein practice. Initially, the gas-lift wells simplyinjected the gas at the bottom of the tubing, but withdeep wells this requires excessively high kick offpressures. Later methods were devised to inject the gasinto the tubing at various depths in the wells to avoidsome of the problems associated with high kick offpressures (see U.S. Patent No. 5,261, 4 69) . 2 01221 4

The most common type of gas-lift well usesmechanical, bellows-type gas-lift valves attached to thetgbing to regulate the flow of gas from the annular spaceinto the tubing string (see U.S. Patent Nos. 5,782,261and 5,425,425). In a typical bellows-type gas-lift valve,the bellows is preset or pre-charged to a certainpressure such that the valve permits communication of gasout of the annular space and into the tubing at the pre-charged pressure. The pressure charge of each valve isselected by a well engineer depending upon the positionof the valve in the well, the pressure head, the physicalconditions of the well downhole, and a variety of otherfactors, some of which are assumed or unknown, or willchange over the production life of the well.

Several problems are common with bellows-type gas-lift valves. First, the bellows often loses its pré-chargé, causing the valve to fail in the closed positionor changing its operating setpoint to other thah thedesign goal. At other times exposure to overpressure maycause the valve to close and become inopérable. Anothercommon failure is érosion around the valve seat anddétérioration of the bail stem in the valve. This oftenleads to partial failure or at least inefficientproduction. Because the gas flow through a gas-lift valveis often not continuous at a steady State, but ratherexhibits a certain amount of hammer and chatter as thevalve rapidly opens and closes, valve dégradation iscommon, leading to valve leakage. Failure or inefficientoperation of bellows-type valves leads to correspondinginefficiencies in operation of a typical gas-lift well.

In fact, it is estimated that well production is at least 5-15% less than optimum because of valve failure or operational inefficiencies. These cannot be corrected since the valve preset pressure is determined at design time, and there is insufficient real-time knowledge of a 3 012214 well's operating State to monitor, prevent or controlinstabilities in the lift process.

Side-pocket mandrels coupled to the tubing string areknown for receiving wireline insertable and retrievablegas-lift valves. Many gas-lift wells hâve gas-lift valvesincorporated as an intégral part of the tubing string,typically mounted to a pipe section. However, wirelinereplaceable side pocket mandrel type of gas-lift valves,such as those manufactured by Camco or Weatherford, hâvemany advantages and are quite common (see U.S. PatentNos. 5,782,261 and 5,797,453). Gas-lift valves placed ina side pocket mandrel can be inserted and removed using awireline and kickover tool either in top or bottom entry.In latéral and horizontal boreholes, coil tubing is usedfor insertion and removal of the gas-lift valves. It iscommon practice in oilfield production to shut offproduction of the well every three to five years and usea wireline to replace gas-lift valves. However, anoperator often does not hâve a good estimate of whichvalves in the well hâve failed or degraded and need to bereplaced.

It would, therefore, be a significant advantage if aSystem and method were devised which overcame theinefficiency of conventional bellows-type gas-liftvalves. Several methods hâve been devised to placecontrollable valves downhole on the tubing string but ailsuch known devices typically use an electrical cabledisposed along the tubing string to power and communicatewith the gas-lift valves. It is, of course, highlyundesirable and in practice difficult to use a cablealong the tubing string either intégral with the tubingstring or spaced in the annulus between the tubing stringand the casing because of the number of failuremechanisms présent in such a System. The use of a cableprésents difficulties for well operators while assembling 4 012214 and inserting the tubing string into a borehole.

Additionally, the cable is subjected to corrosion andhçavy wear due to movement of the tubing string withinthe borehole. An example of a downhole communicationSystem using a cable is shown in PCT/EP97/01621. U.S. Patent No. 4,839,644 describes a method andSystem for wireless two-way communications in a casedborehole having a tubing string. However, this Systemdescribes a communication scheme for coupling electro-magnetic energy in a transverse electric mode (TEM) usingthe annulus between the casing and the tubing. Itrequires a toroidal antenna to launch or receive signaisin a TEM mode, the Patent suggests the need for aninsulated well head, and does not speak to the powersource for a downhole module. The inductive couplingrequires a substantially nonconductive fluid such ascrude oil in the annulus between the casing and thetubing, and this oil must be of a higher density than thebrine so that brine leakage does not gather at the bottomof the annulus. The invention described in U.S. PatentNo. 4,839,644 has not been widely adopted as a practicalscheme for downhole communication because it isexpensive, has problems with brine leakage into thecasing, and is difficult to use. Another System fordownhole communication using mud puise telemetry isdescribed in U.S. Patent Nos. 4,648,471 and 5,887,657.Although mud puise telemetry can be successful at lowdata rates, it is of limited usefulness where high datarates are required or where it is undesirable to hâvecomplex, mud puise telemetry equipment downhole. Othermethods of communicating within a borehole are describedin U.S. Patent Nos. 4,468,665; 4,578,675; 4,739,325;5,130,706; 5,467,083; 5,493,288; 5,574,374; 5,576,703;and 5,883,516. PCT Application WO93/26115 describes acommunication System for use on undersea pipelines which 5 012214 suffers from the need to provide a number of powersources on the pipeline.

It would, therefore, be a significant advance in theoperation of gas-lift wells if an alternative to theconventional bellows type valve were provided, inparticular, if the tubing string and the casing could beused as the communication and power conductors to controland operate a controllable gas-lift valve.

The petroleum well and method according to thepreamble of daims 1 and 5 are known from European patentapplication EP 0721053. In the known assembly and methoda tubular coated by an electrically insulating coating isused in combination with inductive coils that are locatedoutside the coating to transmit electrical power andsignais via the well tubular.

European patent application EP 0964134 discloses amethod wherein electrical signais are transmitted via astring of well tubulars that are also provided with anelectrically insulating coating and that are electricallyinsulated from the other parts of the tubular string byinsulating joints. A disadvantage of the known Systems is that theyinvolve transmission of signais through well tubularsthat are coated by an electrically insulating layer whichis expensive and is prone to wear and damage duringinstallation and use.

SUMMARY OF THE INVENTION

The petroleum well and method according to theprésent invention are characterized by the characterizingfeatures of daims 1 and 9. In an important application,the petroleum well is a controllable gas-lift well whichincludes a piping structure of a cased wellbore having atubing string positioned and longitudinally extending 5a 012214 within the casing. The position of the tubing stringwithin the casing créâtes an annulus between the tubingstring and the casing. A communication System, ortelemetry backbone is provided for supplying power and 5 communication signais downhole. The power is preferably a low voltage, AC current at conventional power frequencies 6 01221 4 in the range 50 to 400 Hertz, but in certain embodimentsDC power may be used.

In a preferred embodiment of the présent invention, alower induction choke of ferromagnetic material isdisposed on the tubing string downhole to act as a sériésimpédance to current flow on the tubing. A hanger forhanging the tubing string within the well bore includesan insulated portion that electrically isolâtes the upperportion of the tubing string near the surface of thewell. Communication preferably takes place on anelectrically isolated section of the tubing stringbetween the insulated portion of the hanger and the lowerferromagnetic choke. Power and communication signais areimparted to the electrically isolated portion of thetubing string and the casing acts as an electricalreturn. A plurality of downhole devices are connected to thetubing string downhole for monitoring and contrôlling theoperation of the well. These downhole devices couldinclude controllable gas-lift valves, sensors, electronics modules, and modems. A controllable gas-liftvalve is coupled to the tubing to control gas injectionbetween the interior and exterior of the tubing, morespecifically, between the annulus and the interior of thetubing. The controllable gas-lift valve is powered andcontrolled from the surface to regulate the fluidcommunication between the annulus and the interior of thetubing. Sensors are located downhole to monitor thedownhole physical conditions of the well. An electronicsmodule is a control unit that receives signais from thesensors for communicating the signais to the surface andreceives communication signais from the surface forcontrolling the controllable gas-lift valve. Modems areused for communicating signais between other downholedevices and the surface. 7 012214

In more detail, a surface computer having a modemimparts a communication signal to the tubing, and thesignal is received by a modem downhole. The downholemodem, which is often a component of the electronicsmodule, then relays the signal to the controllable gas-lift valve. Similarly, the downhole modem can receive andthen communicate sensor information to the surfacecomputer. Depending on the communication range that themodems are capable of providing under spécifie wellconditions, the signais travelling along the tubingstring may be relayed between downhole modems. Power isinput into the tubing string and received downhole tocontrol the operation of the controllable gas-lift valve.

Preferably, a surface computer is coupled via thesurface modem and the tubing to the downhole modems. Thesurface computer can receive measurements from a varietyof sources, such as downhole or surface sensors,measurements of the oil output, and measurements of thecompressed gas input to the well (flow and pressure).Using such measurements, the computer can compute anoptimum position of the controllable gas-lift valve, moreparticularly, the optimum amount of the gas injected fromthe annulus inside the casing through the controllablevalve into the tubing. Additional enhancements arepossible, such as controlling the amount of compressedgas input into the well at the surface, controlling backpressure on the wells, controlling a porous frit orsurfactant injection system to foam the oil, andreceiving production and operation measurements from avariety of other wells in the same field to optimize theproduction of the field.

The ability to actively monitor current conditions downhole, coupled with the ability to control surface and downhole conditions, has many advantages in a gas-lift well. Gas-lift wells hâve four broad régimes of fluid 8 01221 4 flow, for example bubbly, Taylor, slug and annular flow.The downhole sensors of the présent invention enable thedétection and identification of the flow régime. Theabove referenced control mechanisms - surface computer, 5 controllable valves, gas input, surfactant injection,

etc. - provide the ability to attain and maintain optimumflow. In general, well tests and diagnoses may beperformed and analyzed continuously and in real time.BRIEF DESCRIPTION OF THE DRAWINGS 10 Figure 1 is a schematic front view of a controllable gas-lift well according to one embodiment of the présentinvention, the gas-lift well having a tubing string and acasing positioned within a borehole.

Figure 2A is an enlarged cut-away vertical portion of 15 a tubing string in a cased borehole having an induction choke about the tubing.

Figure 2B is an enlarged cut-away horizontal portionof the tubing string of Figure 2A.

Figures 3A and 3B are cross-sectional front views of 20 a controllable valve in a cage configuration according to one embodiment of the présent invention.

Figure 4 is an enlarged schematic front view of thetubing string and casing of Figure 1, the tubing stringhaving an electronics module, sensors, and' a controllable 25 gas-lift valve operatively connected to an exterior of the tubing string.

Figure 5 is a schematic of an équivalent circuitdiagram for the controllable gas-lift well of Figure 1,the gas-lift well having an AC power source, the 30 electronics module of Figure 3A, and the electronics module of Figure 4.

Figure 6 is a System block diagram of an electronicsmodule. 9 01221 4

DETAILED DESCRIPTION OF THE INVENTION

As used in the présent application, a "pipingstructure" can be one single pipe, a tubing string, awell casing, a pumping rod, a sériés of interconnectedpipes, rods, rails, trusses, lattices, supports, a branchor latéral extension of a well, a network of inter-connected pipes, or other structures known to one ofordinary skill in the art. The preferred embodiment makesuse of the invention in the context of an oil well wherethe piping structure comprises tubular, metallic,electrically-conductive pipe or tubing strings, but theinvention is not so limited. For the présent invention,at least a portion of the piping structure needs to beelectrically conductive, such electrically conductiveportion may be the entire piping structure (e.g., steelpipes, copper pipes) or a longitudinal extendingelectrically conductive portion combined with alongitudinally extending non-conductive portion. In otherwords, an electrically conductive piping structure is onethat provides an electrical conducting path from a firstlocation where a power source is electrically connectedto a second location where a device and/or electricalreturn is electrically connected. The piping structurewill typically be conventional round métal tubing, butthe cross-section geometry of the piping structure, orany portion thereof, can vary in shape (e.g., round,rectangular, square, oval) and size (e.g., length,diameter, wall thickness) along any portion of the pipingstructure. Hence, a piping structure must hâve anelectrically conductive portion extending from a firstlocation of the piping structure to a second location ofthe piping structure. A "valve" is any device that functions to regulate the flow of a fluid. Examples of valves include, but are not limited to, bellows-type gas-lift valves and 10 012214 controllable gas-lift valves, each of which may be usedto regulate the flow of lift gas into a tubing string of . a,well. The internai workings of valves can vary greatly,and in the présent application, it is not intended to 5 limit the valves described to any particular configuration, so long as the valve functions to regulateflow. Some of the various types of flow regulatingmechanisms include, but are not limited to, bail valveconfigurations, needle valve configurations, gâte valve 10 configurations, and cage valve configurations. The methods of installation for valves discussed in theprésent application can vary widely. Valves can bemounted downhole in a well in many different ways, someof which include tubing conveyed mounting configurations, 15 side-pocket mandrel configurations, or permanent mounting configurations such as mounting the valve in an enlargedtubing pod.

The term "modem" is used generically herein to referto any communications device for transmitting and/or 20 receiving electrical communication signais via an electrical conductor (e.g., métal). Hence, the term isnot limited to the acronym for a modulator (device thatconverts a voice or data signal into a form that can betransmitted)/demodulator (a device that recovers an 25 original signal after it has modulated a high frequency carrier). Also, the term "modem" as used herein is notlimited to conventional computer modems that couvertdigital signais to analog signais and vice versa (e.g.,to send digital data signais over the analog Public 30 Switched Téléphoné Network). For example, if a sensor outputs measurements in an analog format, then suchmeasurements may only need modulate a carrier signal andbe transmitted—hence no analog-to-digital conversion isneeded. As another example, a relay modem or 35 communication device may only need to identify, filter, 11 01221 4 amplify, and/or retransmit a signal received. However,the modems used in this invention will generally bedigital broadband, since these are widely available fromcommercial sources, and hâve the broadest applicability.

The term "wireless" as used in the présent inventionmeans the absence of a conventional, insulated wireconductor e.g. extending from a downhole device to thesurface. Using the tubing and/or casing as a conductor isconsidered "wireless."

The term "sensor" as used in the présent applicationrefers to any device that detects, détermines, monitors,records, or otherwise senses the absolute value of or achange in a physical quantity. Sensors as described inthe présent application can be used to measure température, pressure (both absolute and differential),flow rate, seismic data, acoustic data, pH level,salinity levels, valve positions, or almost any otherphysical data.

The term "electronics module" in the présentapplication refers to a control device. Electronicsmodules can exist in many configurations and can bemounted downhole in many different ways. In one mountingconfiguration, the electronics module is actually locatedwithin a valve and provides control for the operation ofa motor within the valve. Electronics modules can also bemounted external to any particular valve. Someelectronics modules will be mounted within side pocketmandrels or enlarged tubing pockets, while others may bepermanently attached to the tubing string. Electronicsmodules often are electrically connected to sensors andassist in relaying sensor information to the surface ofthe well. It is conceivable that the sensors associatedwith a particular electronics module may even be packagedwithin the electronics module. Finally, the electronicsmodule is often closely associated with, and may actually 12 01221 4 contain, a modem for receiving, sending, and relayingcommunications from and to the surface of the well.

Signais that are received from the surface by theelectronics module are often used to effect changeswithin downhole controllable devices, such as valves.Signais sent or relayed to the surface by the electronicsmodule generally contain information about downholephysical conditions supplied by the sensors.

The terms "up", "down", "above", "below" as used inthis invention are relative terms to indicate positionand direction of movement, and describe position "alonghole depth" as is conventional in the industry. In highlydeviated or horizontal wells, these terms may or may notcorrespond to absolute relative placement relative to theearth's surface.

Referring to FIG. 1 in the drawings, a petroleum wellaccording to the présent invention is illustrated. ThePetroleum well is a gas-lift well 10 having a borehole 11extending from a surface 12 into a production zone 14that is located downhole. A production platform 20 islocated at surface 12 and includes a hanger 22 forsupporting a casing 24 and a tubing string 26. Casing 24is of the type conventionally employed in the oil and gasindustry. The casing 24 is typically installed insections and is cemented in borehole 11 during wellcompletion. Tubing string 26, also referred to asproduction tubing, is generally a conventional stringcomprising a plurality of elongated tubular pipe sectionsjoined by threaded couplings at each end of the pipesections, but may alternatively be continuously inserted,as coiled tubing for example. Production platform 20 alsoincludes a gas input throttle 30 to control the input ofcompressed gas into an annular space 31 between casing 24and tubing string 26. Conversely, output valve 32 permits 13 012214 the expulsion of oil and gas bubbles from an interior oftubing string 26 during oil production. , Gas-lift well 10 includes a communication System 34for providing power and two-way communication downhole inwell 10. Communication System 34 includes a lowerferromagnetic choke 42 that is installed on tubingstring 26 to act as a sériés impédance to electriccurrent flow. The size and material of ferromagneticchokes 42 can be altered to vary the sériés impédancevalue. Hanger 22 includes an insulated portion 40 thatelectrically insulates tubing string 26 from casing 24and from the remainder of the tubing string located abovesurface 12. The section of tubing string 26 betweeninsulated portion 40 and lower choke 42 may be viewed asa power and communications path (see also FIG. 5). Lowerchoke 42 is manufactured of high permeability magneticmaterial and is mounted concentric and external to tubingstring 26. Choke 42 is typically insulated with shrink-wrap plastic film and may be hardened with epoxy towithstand rough handling. A computer and power source 44 having power andcommunication feeds 46 is disposed outside of borehole 11at surface 12. Communication feeds 46 pass through apressure feed 47 located in hanger 22 and are electrically coupled to tubing string 26 below insulatedportion 40 of hanger 22. Power and communications signaisare supplied to tubing string 26 from computer and powersource 44.

Referring to FIGS. 2A and 2B in the drawings,choke 42 comprises a toroid concentric with the tubingstring 26 and within the annular space 31 between tubingstring 26 and well casing 24. Choke 42 functions bycreating a back-e.m.f. in tubing string 26 that opposesthe e.m.f. from power source 44. The back-e.m.f iscreated by the magnetic flux changes in the choke, and by 14 012214

Faraday's Law of Induction this e.m.f. is proportional tothe value of the magnetic flux and by its rate of changewith time. When the pipe sections above the insulatedportion 40 and below the lower choke 42 are grounded, theback-e.m.f. induced by lower choke 42 acts to opposetransmission of power and communications in a time-varying current through the choke 42. This effectivelyforms an isolated tubing section between insulatedportion 40 and lower chokes 42. When the choke designcréâtes a significant degree of isolation, the back-e.m.f. is close to the value of the imposed e.m.f. To thedegree that the back-e.m.f. is less than the imposede.m.f., the différence of the two allows a leakagecurrent to flow through the choke section of the tubing.This power is lost, but is essential to the operation ofthe choke, because it is the magnetic flux from thisleakage current passing through the choke that créâtesthe back-e.m.f. in the choke section. Thus, the designgoal is to create an induction choke that generates aback-e.m.f. as efficiently as possible from the leakagecurrent. FIGS. 2A and 2B show a basic choke design andindicate the variables used in the design analysis. Thedefining variables and a self-consistent set of physicalunits are: L = length of choke, meters;a = choke inner radius, meters;b = choke outer radius, meters;r = distance from choke axis, meters; I = r.m.s. leakage current through choked pipe section, Amperes; ω = angular frequency of leakage current, radians per second; and μ = absolute magnetic permeability of choke material at radius r, Henries per meter. 15 012214

By définition, ω = 2πί, where f = frequency in Hertz.At a distance r from the leakage current (I), the r.m.s.free space magnetic field (H), in Amperes per meter, isgiven by: 5 H = I/2ur.

The magnetic field (H) is circularly symmetric aboutthe choke axis, and can be visualized as magnetic linesof force forming circles around that axis.

For a point within the choke material, the r.m.s. 10 magnetic field (B), in Teslas (Webers per square meter), is given by: B = μΗ = gl/2nr.

The r.m.s. magnetic flux (F) contained within thechoke body, in Webers, is given by:

15 F = J B dS where S is the cross-sectional area of the choke insquare meters as shown in FIG. 3A, and the intégration isover the area S. Performing the intégration from theinner radius of the choke (a) , to the outer radius of the 20 choke (b), over the length of the choke (L) , provides: F = gLI ln (b/a)/2π where ln is the natural logarithm function.

The back-e.m.f. voltage generated by the magneticflux (F), in Volts, is given by: 25 V = coF = 2πί F = gLIf ln(b/a) .

Note that the back-e.m.f. (V) is directly proportional tothe length (L) of the choke for constant values of a andb, the ferrite element internai and external radii. Thusby altering the length of the choke (L), any desired 30 back-e.m.f. (V) can be generated for a given leakage current (I).

Power can be transmitted at a certain frequency rangewithin a functional bandwidth, and the communications canbe transmitted at another frequency range within the same

35 functional bandwidth. Because the frequency of the AC 16 01221 4 power is generally lower than that of the communicationsbandwidth provided, the AC power frequency will oftendétermine the lower bound of the frequency range overwhich electrical isolation is required. Because the 5 electrical impédance of a choke rises linearly with frequency, if the choke provides adéquate impédance atthe AC power frequency, typically it will also beadéquate at the higher frequencies used for communication. However, ferromagnetic materials are10 characterized by a maximum operating frequency above which ferromagnetic properties are not exhibited. Thusthe upper frequency bound of the ferromagnetic materialchosen for the choke construction must be adéquate toprovide isolation at the upper bound of the communication 15 band.

The method of electrically isolating a section of thetubing string as shown in FIG.l is not the sole method ofproviding power and communications signais downhole.Instead of using a hanger 22 with an insulated 20 portion 40, an upper ferromagnetic choke (not shown) could be disposed around tubing string 26. Similarly, anelectrically insulating connector could be used downholein place of lower ferromagnetic choke 42. In thepreferred embodiment shown in FIG. 1, power and 25 communication signais are supplied on tubing string 26, with the electrical return being provided by casing 24.Instead, the electrical return could be provided by anearthen ground. An electrical connection to earthenground could be provided by passing a wire through 30 casing 24 or by connecting the wire to the tubing string below lower choke 42 (if the lower portion of the tubingstring was grounded).

An alternative power and communications path could beprovided by the casing 24. In a configuration similar to 35 that used with tubing string 26, a portion of casing 24 17 012214 could be electrically isolated to provide a telemetrybackbone for transmitting power and communication signaisdçwnhole. If ferromagnetic chokes were used to isolate aportion of the casing, the chokes would be disposed 5 concentrically around the outside of the casing. Instead of using chokes with the casing 24, electricallyisolating connectors could be used similar to isolatedportion 40 of hanger 22. In embodiments using casing 24to supply power and communications signais downhole, an 10 electrical return could be provided either via the tubing string 26 or via an earthen ground. A packer 48 is placed within casing 24 downhole belowlower choke 42. Packer 48 is located above productionzone 14 and provides hydraulic isolation between 15 production zone 14 and the well space above it. The packer electrically connects métal tubing string 26 tométal casing 24. Typically, the electrical connectionsbetween tubing string 26 and casing 24 would not’ allowelectrical signais to be transmitted or received up and 20 down borehole 11 using tubing string 26 as one conductor and casing 24 as another conductor. However, thedisposition of insulated portion 40 and lower ferro-magnetic choke 42 create an electrically isolated sectionof the tubing string 26, which provides a system and 25 method to provide power and communication signais up and down borehole 11 of gas-lift well 10.

Referring still to FIG. 1 in the drawings, aplurality of downhole devices 50 is electrically coupledto tubing string 26 between insulated portion 40 and 30 lower ferromagnetic choke 42. Some of the downhole devices 50 comprise controllable gas-lift valves. Otherdownhole devices 50 may comprise electronics modules,sensors, communication devices (typically broadbanddigital modems), or conventional valves. Although power 35 and communication transmission take place on the 18 012214 electrically isolated portion of the tubing string, downhole devices 50 may be mechanically coupled above orbelow lower choke 42.

Referring to FIGS. 3A and 3B in the drawings, theinstallation of one of the downhole devices (analogous todownhole devices 50 in FIG. 1) is illustrated in moredetail. As mentioned previously, conventional bellows-type gas-lift valves are often used in gas-lift wells toadmit pressurized gas from annular space 31 to the insideof tubing string 26. In the présent invention, any or ailof the conventional valves can be replaced with controllable gas-lift valves. In FIGS. 3A and 3B, acontrollable valve 220 according to the présent inventionis illustrated. Controllable valve 220 includes ahousing 222 and is slidably received in a side pocketmandrel 224. Side pocket mandrel 224 includes a housing 226 having a gas inlet port 228 and a gas outletport 230. When controllable valve 220 is in an openposition, gas inlet port 228 and gas outlet port 230provide fluid communication between annular space 31 andan interior of tubing string 26. In a closed position,controllable valve 220 prevents fluid communicationbetween annular space 31 and the interior of tubingstring 26. In a plurality of intermediate positionslocated between the open and closed positions,controllable valve 220 meters the amount of gas flowingfrom annular space 31 into tubing string 26 through gasinlet port 228 and gas outlet port 230. A stepper motor 234 is disposed within housing 222 ofcontrollable valve 220 for rotating a pinion 236.

Pinion 236 engages a worm gear 238, which in turn raises and lowers a cage 240. When valve 220 is in the closed position, cage 240 engages a seat 242 to prevent flow into an orifice 244, thereby preventing flow through valve 220. This "cage" valve configuration is believed to 19 012214 be a préférable design from a fluid mechanics view whencompared to the alternative embodiment of a needle valveconfiguration. More specifically, fluid flow from inletport 228, past the cage and seat juncture (240, 242)permits précisé fluid régulation without undue fluid wearon the mechanical interfaces. It should be apparent toone skilled in the art that needle valve designs or othervalve designs could be employed.

Controllable valve 220 includes a check valvehead 250 disposed within housing 222 below cage 240. Aninlet 252 and an outlet 254 cooperate with gas inletport 228 and gas outlet port 230 when valve 220 is in theopen position to provide fluid communication betweenannulus 31 and the interior of tubing string 26. Checkvalve head 250 insures that fluid flow only occurs whenthe pressure of fluid in annulus 31 is greater than thepressure of fluid in the interior of tubing string 26.

An electronics module 256 is disposed within thehousing of controllable valve 220. Electronics module 256is operatively connected to valve 220 for communicationbetween the surface of the well and the valve. Theelectronics module 256 contains a spread spectrumcommunication device for receiving power and communicating on tubing string 26 as previously described. In addition to sending signais to the surfaceto communicate downhole physical conditions, theelectronics module can receive instructions from thesurface and adjust the operational characteristics of thevalve 220.

Valve 220 is physically located below lower choke 42but is electrically coupled to tubing string 26 above thechoke 42 by a jumper wire 64. A ground wire 66 iselectrically connected between valve 220 and a bow springcentralizer 60 in order to provide an electrical returnfor valve 220. Bow spring centralizer 60 is used to 20 01221 4 center tubing string 26 relative to casing 24. Whenlocated in the electrically isolated portion of thetubing string 26, each bow spring centralizer 60 includesPVC insulators 62 to electrically isolate casing 24 fromtubing string 26.

Referring to FIG. 4 in the drawings, an alternativeinstallation of several downhole devices (analogous todownhole devices 50 in FIG. 1) is illustrated. Tubingstring 26 includes an annularly enlarged pocket, orpod 100 formed on the exterior of tubing string 26.Enlarged pocket 100 includes a housing that surrounds andprotects a controllable gas-lift valve 99 (schematicallyillustrated) and an electronics module 106. In thismounting configuration, gas-lift valve 99 and electronicsmodule 106 are rigidly mounted to tubing string 26 andare not insertable and retrievable by wireline.Alternatively, valve 99 and electronics module 106 may bydisposed in a side-pocket mandrel (not shown) so that thedevices can be easily inserted and removed by wireline. Aground wire 102 (similar to ground wire 66 of FIG. 3B) isfed through enlarged pocket 100 to connect electronicsmodule 106 to bow spring centralizer 60, which isgrounded to casing 24. Electronics module 106 is externalto valve 99 and is rigidly connected to tubing string 26for receiving communications and power via a power andsignal jumper 104.

Controllable valve 99 includes a motorized cage valvehead 108 and a check valve head 110 that areschematically illustrated in FIG. 4. Cage valve head 108and check valve head 110 operate in a similar fashion tocage 240 and check valve head 250 of FIG. 3A. The valveheads 108, 110 cooperate to control fluid communicationbetween annular space 31 and the interior of tubingstring 26. 21 012214 A plurality of sensors are used in conjunction withelectronics module 106 to control the operation ofcontrollable valve 99 and gas-lift well 10. Pressuresensors, such as those produced by Three MeasurementsSpecialties, Inc., can be used to measure internai tubingpressure, internai pod housing pressures, anddifferential pressures across gas-lift valves. Incommercial operation, the internai pod pressure isconsidered unnecessary. A pressure sensor 112 is rigidlymounted to tubing string 26 to sense the internai tubingpressure of fluid within tubing string 26. A pressuresensor 118 is mounted within pocket 100 to détermine thedifferential pressure across cage valve head 108. Bothpressure sensor 112 and pressure sensor 118 areindependently electrically coupled to electronicsmodule 106 for receiving power and for relayingcommunications. Pressure sensors 112, 118 are podded towithstand the severe vibration associated with gas-lifttubing strings.

Température sensors, such as those manufactured byFour Analog Devices, Inc. {e.g. LM-34) are used tomeasure the température of fluid within the tubing,housing pod, power transformer, or power supply. Atempérature sensor 114 is mounted to tubing string 26 tosense the internai température of fluid within tubingstring 26. Température sensor 114 is electrically coupledto electronics module 106 which receives power and relayscommunications. The température transducers used downholeare rated for -50 to 300 °F and are conditioned by inputcircuitry to +5 to +255 °F. The raw voltage developed ata power supply in electronics module 106 is divided in arésistive divider element so that 25.5 volts will producean input to the analog/digital converter of 5 volts. A salinity sensor 116 is also electrically connectedto electronics module 106. Salinity sensor 116 is rigidly 22 012214 and sealingly connected to th'e housing of enlarged pocket 100 to sense the salinity of the fluid in açnulus 31.

It should be understood that the alternateembodiments illustrated in FIGS. 3B and 4 could includeor exclude any number of the sensors 112, 114, 116 or118. Sensors other than those displayed could also beemployed in either of the embodiments. These couldinclude gauge pressure sensors, absolute pressuresensors, differential pressure sensors, flow ratesensors, tubing acoustic wave sensors, valve positionsensors, or a variety of other analog signal sensors.Similarly, it should be noted that while electronicsmodule 256 shown in FIG. 3B is packaged within valve 220,an electronics module similar to electronics module 106could be packaged with various sensors and deployedindependently of controllable valve 220.

Referring now to FIG. 5 in the drawings, an"équivalent circuit diagram for gas-lift well 10 isillustrated and should be compared to FIG. 1. Computerand power source 44 includes an AC power source 120 and amodem 122 electrically connected between casing 24 andtubing string 26. As discussed previously, electronicsmodule 256 is mounted internally within a valve housingthat is wireline insertable and retrievable downhole.Electronics module 106 is independently and permanentlymounted in an enlarged pocket on tubing string 26.

For purposes of the équivalent circuit diagram ofFIG. 5, it is important to note that electronicsmodules 256, 106 appear identical, both modules 256, 106being electrically connected between casing 24 and tubingstring 26. Electronics modules 256, 106 may contain oromit different components and combinations such assensors 112, 114, 116, 118. Additionally, the electronicsmodules may or may not be an intégral part of a 23 012214 controllable valve. Each electronics module includes apower transformer 124 and a data transformer 128. Datatransformer 128 is electrically coupled to modem 130.

Computer and power source 44 also includes a surfacecontroller (not shown in FIG. 5), which is electricallycoupled via a surface communication device (e.g.,modem 122) and the tubing string 26 and/or casing 24 to adownhole communication device (e.g., modem 130). Eachmodem 130 may communicate with modem 122 either directly,or by relay through intermediate communication devices(comprising e.g., modems, filters, data transformers,amplifiers) to relay a signal as required to effectchanges in the operation of the well. For example, asurface computer can receive measurements from a varietyof sources, such as the downhole sensors, measurements ofthe oil output, and measurements of the compressed gasinput to the well (flow and pressure). Using suchmeasurements, the computer can compute an optimumposition of a controllable gas valve, more particularly,the optimum amount of the gas injected from annularspace 31 through each controllable valve into tubingstring 26. Additional parameters may be controlled by thecomputer, such as controlling the amount of compressedgas input into the well at the surface, controlling backpressure on the wells, controlling a porous frit orsurfactant injection System to foam the oil, andreceiving production and operation measurements from avariety of other wells in the same field to optimize theproduction of the field or production zone.

Depending on the communication range that themodems 130 are capable of providing under spécifie wellconditions, the transmission of sensor and control dataup and down the well may require that these signais berelayed between modems 130 rather than passed directlyfrom the surface to the selected downhole devices 50 (see 24 01221 4

Figure 1). This relay method can be applied to bothconventional and multilatéral well complétions. , Preferably the downhole modems 130 are placed so thateach can communicate with the next two modems up the welland the next two modems down the well. This redundancyallows communications to remain operational even in theevent of the failure of one of the downhole modems 130.

The ensemble of downhole devices 50 having modems 130can provide a permanent telemetry backbone that can bepart of the infrastructure of the well. Such a telemetrybackbone may provide a means to measure the conditions ineach part of the well and transmit the data to a surfacecomputer or a downhole controller, and for the computerto transmit control signais to open or close downholevalves to set back pressure, set gas injection rate,adjust flow rates, and so on. This level of controlallows production from the well to be optimized againstcriteria that may be dynamically managed in substantiallyreal-time, rather than being fixed by a static productiongoal. For instance, the optimum under one set of économieconditions may be maximum recovery from the réservoir,but under different économie conditions it may bebénéficiai to alter the production method to minimize thecost of recovery by using lift gas to maximum effect.

Referring to FIG. 6 in the drawings, electronicsmodule 106 is illustrated in more detail. Although thecomponents of any particular electronics module may vary,the components shown in FIG. 6 could be présent inelectronics modules packaged inside the housing of avalve (such as electronics module 256) or electronicsmodules that are external to a valve. Amplifiers andsignal conditioners 180 are provided for receiving inputsfrom a variety of sensors such as tubing température,annulus température, tubing pressure, annulus pressure,lift gas flow rate, valve position, salinity, 25 01221 4 differential pressure, acoust'ic readings, and others.

Some of these sensors are analogous to sensors 112, 114,13,6, and 118 shown in FIG. 4. Preferably, any low noiseoperational amplifiers are configured with non-invertingsingle ended inputs (e.g. Linear Technology LT1369). Ailamplifiers 180 are programmed with gain éléments designedto convert the operating range of an individual sensorinput to a meaningful 8 bit output. For example, one psiof pressure input would produce one bit of digitaloutput, 100 degrees of température will produce 100 bitsof digital output, and 12.3 volts of raw DC voltage inputwill produce an output of 123 bits. Amplifiers 180 arecapable of rail-to-rail operation.

Electronics module 106.is electrically connected tomodem 122 via casing 24 and tubing string 26. Addressswitches 182 are provided to address a particular devicefrom modem 122. As shown in FIG. 6, 4 bits of addressesare switch selectable to form the upper 4 bits o’f afull 8 bit address. The lower 4 bits are implied and areused to address the individual éléments within eachelectronics module 106. Thus, using the configurationillustrated, sixteen modules are assigned to a singlemodem 122 on a single communications line. As configured,up to four modems 122 can be accommodated on a singlecommunications line.

Electronics module 106 also includes a programmableinterface controller (PIC) 170, which preferably has abasic clock speed of 20 MHz and is configured with 8analog-to-digital inputs 184 and 4 address inputs 186. PIC 170 includes a transistor-transistor level (TTL)serial communications, universal asynchronous receiver-transmitter UART 188, as well as a motor controllerinterface 190. PIC 170 is electrically coupled to amodem 171 (analogous to modem 130 of FIG. 5) thatcommunicates with modem 122. 26 012214

Electronics module 106 al'so contains a powersupply 166. A nominal 6 volts AC line power is suppliedtç power supply 166 along tubing string 26. Powersupply 166 couverts this power to plus 5 volts DC atterminal 192, minus 5 volts DC at terminal 194, andplus 6 volts DC at terminal 196. A ground terminal 198 isalso shown. The converted power is used by variouséléments within electronics module 106.

Although connections between power supply 166 and thecomponents of electronics module 106 are not shown, thepower supply 166 is electrically coupled to the followingcomponents to provide the specified power. PIC 170 usesplus 5 volts DC, while modem 171 uses plus 5 and minus5 volts DC. A motor 199 (analogous to stepper motor 234of FIG. 3A) is supplied with plus 6 volts DC fromterminal 196. Power supply 166 comprises a step-uptransformer for converting the nominal 6 volts AC to7.5 volts AC. The 7.5 volts AC is then rectified’ in afull wave bridge to produce 9.7 volts of unregulated DCcurrent. Three-terminal regulators provide the regulatedoutputs at terminais 192, 194, and 196 which are heavilyfiltered and protected by reverse EMF circuitry.

Modem 171 is the major power consumer in electronicsmodule 165, typically using 350+ milliamps at plus/minus5 volts DC when transmitting.

Modem 171 is a digital broad-band modem having anIC/SS power line carrier chip set such as modelsEG ICS1001, ICS1002 and ICS1003 manufactured by NationalSemiconductor. Modem 171 is capable of 300-3200 baud datarates at carrier frequencies ranging from 14 kHz to76 kHz. Ü.S. Patent No. 5,488,593 describes the chip setin more detail and is incorporated herein by reference.There exist alternative implémentations of suitablemodems based on various transmission principles, bothbroadband and narrow-band, which are commercially 27 01221 4 available and which would be’suited to the purpose ofproviding bi-directional communications between modems. PIC 170 Controls the operation of stepper motor 199through a stepper motor controller 200 such as modelSA1042 manufactured by Motorola. Controller 200 needsonly directional information and simple clock puises fromPIC 170 to drive stepper motor 199. An initial setting ofcontroller 200 conditions ail éléments for initialoperation in known States. Stepper motor 199, preferablya MicroMo gear head, positions a cage valve head 201(analogous to cage 240 of FIG. 3A), which is theprincipal operative component of the controllable gas-lift valve. Stepper motor 199 provides 0.4 inch-ounce oftorque and may be operated at up to 500 steps per second.A complété révolution of stepper motor 199 consists of24 individual steps, and the gearhead provides amechanical réduction of 989:1, providing a maximum speedof 1 révolution per minute at the gearhead output shaftat a torque of 24 inch-pounds, which is more thansufficient to seat and unseat valve 201. While thisillustrative example of a suitable embodiment is based onthe use of a stepper motor, it is important to note thatthere exist alternative methods for electronic controlappropriate to other types of motors, many of which wouldbe suitable for the purpose of controlling the degree ofopening of valve 201. PIC 170 communicates through digital modem 171 tomodem 122 via casing 24 and tubing string 26. PIC 170uses a MODBUS 584/985 PLC communications protocol. Theprotocol is ASCII encoded for transmission.

OPERATION A large percentage of the artificially lifted oil production today uses gas-lift to help bring the réservoir oil to the surface. In such gas-lift wells, compressed gas is injected downhole outside the tubing, 28 01221 4 usually in the annulus betweèn the casing and the tubing,and mechanical gas-lift valves permit communication ofthe gas into the tubing section, thus inducing the riseof the fluid column within the tubing to the surface. Aspreviously described, conventional mechanical gas-liftvalves are unreliable because of leakage and failures.

Such leaks and failures are not readily détectable at thesurface and probably reduce a well's productionefficiency on the order of 15 percent through lowerproduction rates and higher demands on the field lift gascompression Systems.

The wireless telemetry backbone of the présentinvention provides a System for monitoring andcontrolling the operation of a gas-lift well. By placingdownhole devices, such as sensors, electronics modules,controllable gas-lift valves, and modems on the tubingstring of the well, the well can be accurately monitoredand changes can be made to promote efficient production.Each of the individual downhole devices is individuallyaddressable via wireless communication through the tubingand casing. That is, a modem at the surface and anassociated controller communicates to a number ofdownhole modems. When the surface modem is communicatingwith a particular downhole modem, other downhole modemscan act as intermediates by relaying signais as needed.Sensors report such measurements as downhole tubingpressures, downhole casing pressures, downhole tubing andcasing températures, lift gas flow rates, gas valveposition, and acoustic data (see Fig. 4, sensors 112, 114, 116, and 118). The surface computer (either local atthe wellhead or centrally located in a producing field)continuously combines and analyzes the downhole data aswell as surface data, to compute a real-time tubingpressure profile. An optimal gas-lift flow rate for eachcontrollable gas-lift valve is computed from this data. 29 012214

Alternatively, the sensors mày report their measurementsvia repeater downhole modems to a controller associatedw$th a gas-lift valve to similarly control the operationof the valve for optimal or desired flow rates.

In addition to controlling the flow rate of the well,production may be controlled to produce an optimum fluidflow State. Unwanted conditions such as "heading" and"slug flow" can be avoided. As previously mentioned, itis possible to attain and maintain the optimum flowrégime appropriate to the desired production rate of awell. By being able to détermine unwanted flow conditionsquickly downhole, production can be controlled to avoidsuch unwanted conditions. A fast détection by the surfacecomputer of flow conditions allows the computer tocorrect any flow problems by adjusting such factors asthe position of the controllable gas-lift valve, the gasinjection rate, back pressure on tubing at the wellhead,and even injection of surfactant.

Even though many of the examples discussed herein areapplications of the présent invention in petroleum wells,the présent invention also can be applied to other typesof wells, including but not limited to water wells andnatural gas wells.

One skilled in the art will see that the présentinvention can be applied in many areas where there is aneed to provide a controllable valve within a borehole,well, or any other area that is difficult to access.

Also, one skilled in the art will see that the présentinvention can be applied in many areas where there is analready existing conductive piping structure and a needto route power and communications to a controllable valvein a same or similar path as the piping structure. Awater sprinkler System or network in a building forextinguishing fires is an example of a piping structurethat may be already existing and may hâve a same or 30 012214 similar path as that desired for routing power andcommunications to a controllable valve. In such caseanother piping structure or another portion of the samepiping structure may be used as the electrical return.

Claims (14)

31 01221 4

1. A petroleum well having a wellbore (11) extending inthe earth and electrically conductive piping structure(26) disposed in the wellbore (11), wherein one or moredevices (50) are electrically coupled to the pipingstructure (26) in the wellbore for wireless réception ofa time-varying electrical signal applied to the pipingstructure (26) and at least one device (50) for sensingor controlling a physical characteristic in or proximatethe wellbore is powered by-the signal, and wherein aninduction choke is located proximate a portion of thepiping structure to route the time varying signal withinthe piping structure; characterized in that the inductionchoke (42) acts as a sériés impédance to electricalcurrent flow through said portion of the piping structure(26) .

2. The petroleum well in accordance with claim 1,wherein the piping structure (26) is a production tubingstring (26) which is surrounded by a fluid filled annulus(31) and a casing (24).

3. The petroleum well in accordance with claim 1,wherein a device (44) is opérable to apply a time-varyingelectrical signal to the piping structure to transmitinformation.

4. The petroleum well in accordance with claim 1,wherein the device is a sensor for sensing a physicalcharacteristic in the wellbore such as température,pressure, or acoustic.

5. The petroleum well in accordance with claim 1,wherein the device is a valve which opérâtes when 32 012214 commanded by a wireless signal applied to the pipingstructure.

6. The petroleum well in accordance with claim 1,wherein the petroleum well is a gas lift well, the pipingstructure includes tubing and one device is a gas liftvalve coupled to the tubing and adjustable to regulatethe fluid flow between the interior and exterior of thetubing.

7. The petroleum well in accordance with claim 1,including a plurality of devices each adapted to send andreceive communication signais for communicating withother devices in different régions of the well.

8. The petroleum well in accordance with claim 1,including a controller and some of the devices beingsensors and at least one device being a valve, wherebythe operation of the valve is determined by thecontroller based on input from the sensors.

9. In a petroleum well having a wellbore extending inthe earth and electrically conductive piping structuredisposed in the wellbore, a method of operating thewellbore by applying a time varying electrical signal tothe piping structure which is received by one or morewireless devices electrically coupled to the pipingstructure in the wellbore to effect the operation of atleast one device in the earth and wherein an inductionchoke is located proximate a portion of the pipingstructure to route the time varying signal within thepiping structure; characterized in that the inductionchoke (42) acts as a sériés impédance to electricalcurrent flow through said portion of the piping structure(26) .

10. The method of claim 9, a device comprising a sensor,the method including sensing a physical characteristic 33 012214 such as température, pressure, or acoustic, andcommunicating such physical characteristic along thepiping structure.

11. The method of claim 9, wherein a tinte varying power 5 signal and a tinte varying communication signal is applied to the piping structure to power and communicate with anumber of devices.

12. The method of claim 9, wherein the petroleum well isgas-lift and at least one device is a controllable valve, 10 including communicating with the valve and regulating the fluid flow through the valve.

13. The method of claim 12, including controlling theoperation of the gas-lift well.

14. The method of claim 13, wherein the operation 15 includes the unloading, kickoff, or production of the well.