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BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates generally to the field of well cleaning, and more specifically to modified coiled tubing apparatus and methods of using same in well cleaning operations. 
         [0003]    2. Related Art 
         [0004]    The ability to pump fluid while conveying tools makes wellbore cleanouts a natural application for coiled tubing (CT). During a conventional cleanout, fluid is pumped through the CT, often across a nozzle, and into the annulus, lifting solid particles to surface. Certain well types or conditions, however, make conventional cleanouts difficult or ineffective. For example, in wells where the CT outside diameter is small relative to the annulus internal diameter, it may be difficult to achieve the flow rate needed to lift particles in the annulus as the annular velocity is quite low. 
         [0005]    In wells where conventional cleanouts are impractical, reverse circulation sometimes provides a means to lift solids to the surface. In reverse circulation, fluid at surface is pumped into the annulus, where it then flows down the well and into the CT, lifting particles in the process. Because the fluid velocity in the CT is much higher than in the annulus at the same flow rate, particles are more easily suspended and moved along. Using standard surface equipment, the particles are collected and disposed of with minimal disruption to normal well processes. 
         [0006]    The main concern with reverse circulating is the safety risk associated with allowing fluid to flow from downhole to surface through the CT. A potential well must meet strict qualifications before a reverse cleanout is performed in order to minimize this risk. Current reversing tools are not adequate in many situations since they require either CT manipulation or pumping to return to a safe position, a hazardous situation arises if these functions are lost during the job. Also, presently known reversing tools can potentially allow hydrocarbons to flow up the CT to surface; the hydrocarbons can only be detected when they reach surface and already present a potential well control situation. 
         [0007]    From the above it is evident that there is a need in the art for improvement in well cleaning. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with the present invention, apparatus (also referred to herein as reversing tools, or simply tools) and methods are described that reduce or overcome problems in previously known apparatus and methods. 
         [0009]    A first aspect of the invention are apparatus comprising:
   An apparatus comprising:
       (a) a section of coiled tubing having a main flow passage;   (b) at least two flow-preventing valves in the section of coiled tubing, each adapted to close the main flow passage upon attempted flow reversal; and   (c) at least one actuator adapted to deter closing of the flow-preventing valves.   
       
 
         [0014]    Apparatus of the invention include those apparatus wherein the reversing tool apparatus may be referred to as “intrinsically safe”, in that they do not rely on pumping or CT manipulation to return to a safe mode of operation. The inventive apparatus and methods employ one or more forms of actuation, for example motor and solenoid actuators. Motors and solenoids may be used with several types of mechanical systems to achieve the desired result. 
         [0015]    The inventive apparatus may further include a hydraulic system used in conjunction with these actuation systems. A pressure lock piston, forced up by a spring, may allow hydraulic fluid to flow freely into a compensation chamber, so that there is no pressure differential across a hydraulic fluid check valve, which may be a ball and spring combination. In its down position, the pressure lock piston only allows flow across the hydraulic fluid check valve in one direction, from the compensation chamber into a high pressure chamber. The pressure lock piston is normally forced up by the spring. When the hydraulic fluid pressure above pressure lock piston is higher than the annulus (outside the tool) pressure below the piston, the spring can be overridden and pressure lock piston may move down. When a pressure differential is seen across the hydraulic fluid check valve assembly, a solenoid may be activated, causing its actuator to move toward a ball to roll the ball off its seat and release the hydraulic pressure. A compensating piston may provide an adequate supply of hydraulic fluid for the system. The compensating piston allows for direct pressure transfer from the tool ID above a flow-preventing valve to the hydraulic fluid. 
         [0016]    Apparatus of the invention may include surface/tool communication through one or more communication links, including but not limited to hard wire, optical fiber, radio, or microwave transmission. The inventive apparatus and methods may include a chemical detector at the tool level, which enables an operator to stop reversing long before hydrocarbons or other chemicals can reach surface and pose a safety risk. The chemical detector, if used, may be selected from any functioning system, or future functioning system, or combination of systems. 
         [0017]    Another aspect of the invention is a method, one method of the invention comprising:
       (a) inserting a coiled tubing having a main flow channel into a bore hole, the coiled tubing comprising a section of coiled tubing having at least two flow-preventing valves;   (b) initiating flow of a fluid through an annulus between the coiled tubing and the well bore; and   (c) reversing flow through the coiled tubing by actuating at least one actuator to deter closing of the flow-preventing valves.       
 
         [0021]    Methods of the invention include those comprising sensing a chemical, such as a hydrocarbon, in the reverse flow. 
         [0022]    Apparatus and methods of the invention will become more apparent upon review of the brief description of the drawings, the detailed description of the invention, and the claims that follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The manner in which the objectives of the invention and other desirable characteristics can be obtained is explained in the following description and attached drawings in which: 
           [0024]      FIGS. 1A and 1B  are schematic cross-sectional views of a prior art flapper check valve useful in the invention; 
           [0025]      FIGS. 2A and 2B  are schematic cross-sectional views of a prior art dart valve useful in the invention; 
           [0026]      FIG. 3  is a schematic cross-sectional view of one possible hydraulic system useful in the apparatus and methods of the invention; 
           [0027]      FIGS. 3A ,  2 B,  3 C, and  3 D are schematic cross-sectional views of the hydraulic system of  FIG. 3  in different modes of operation; 
           [0028]      FIGS. 4A ,  4 B, and  4 C are schematic cross-sectional views of a first apparatus embodiment of the invention on different modes of operation; 
           [0029]      FIGS. 5 and 6  are schematic cross-sectional views of apparatus of the invention comprising motor and dual solenoid actuators, respectively; 
           [0030]      FIGS. 7-14  are schematic cross-sectional views of other apparatus embodiment of the invention; and 
           [0031]      FIG. 15  is a logic diagram illustrating some of the features of the invention. 
       
    
    
       [0032]    It is to be noted, however, that the appended drawings are not to scale and illustrate only typical embodiments of this invention, and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       DETAILED DESCRIPTION 
       [0033]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
         [0034]    All phrases, derivations, collocations and multiword expressions used herein, in particular in the claims that follow, are expressly not limited to nouns and verbs. It is apparent that meanings are not just expressed by nouns and verbs or single words. Languages use a variety of ways to express content. The existence of inventive concepts and the ways in which these are expressed varies in language-cultures. For example, many lexicalized compounds in Germanic languages are often expressed as adjective-noun combinations, noun-preposition-noun combinations or derivations in Romanic languages. The possibility to include phrases, derivations and collocations in the claims is essential for high-quality patents, making it possible to reduce expressions to their conceptual content, and all possible conceptual combinations of words that are compatible with such content (either within a language or across languages) are intended to be included in the used phrases. 
         [0035]    The invention describes modified coiled tubing (CT) apparatus and methods for cleaning wellbores using same. As used herein the term “cleaning” means removing, or attempting to remove, unwanted material in a wellbore. A “wellbore” may be any type of well, including, but not limited to, a producing well, a non-producing well, an experimental well, and exploratory well, and the like. Wellbores may be vertical, horizontal, some angle between vertical and horizontal, and combinations thereof, for example a vertical well with a non-vertical component. During a conventional cleanout, fluid is pumped through the CT, often across a nozzle, and into the annulus, lifting solid particles to surface. Certain well types or conditions, however, make conventional cleanouts difficult or ineffective. For example, in wells where the CT outside diameter is small relative to the well internal diameter, it may be difficult to achieve the flow rate needed to lift particles in the annulus as the annular velocity is quite low. In wells where conventional cleanouts are impractical, reverse circulation sometimes provides a means to lift solids to the surface. In reverse circulation, fluid at surface is pumped into the annulus, where it then flows down the well and into the CT, lifting particles in the process. Because the fluid velocity in the CT is much higher than in the annulus at the same flow rate, particles are more easily suspended and moved along. Using standard surface equipment, the particles are collected and disposed of with minimal disruption to normal well processes. The main concern with reverse circulating is the safety risk associated with allowing fluid to flow from downhole to surface through the CT. A potential well must meet strict qualifications before a reverse cleanout is performed in order to minimize this risk. Current reversing tools are not adequate in many situations since they require either CT manipulation or pumping to return to a safe position, a hazardous situation arises if these functions are lost during the job. Also, presently known reversing tools can potentially allow hydrocarbons to flow up the CT to surface; the hydrocarbons can only be detected when they reach surface and already present a potential well control situation. 
         [0036]    Given that safety is a primary concern, and that there is considerable investment in existing equipment, it would be an advance in the art if reverse well cleanouts could be performed using existing apparatus modified to increase safety and efficiency during the cleaning procedures, with minimal interruption of other well operations. This invention offers methods and apparatus for these purposes. The American Petroleum Institute (API) requires that downhole tools be equipped with two barriers that independently prevent fluid from flowing back to surface through the CT. These barriers usually take the form of check valves. If fluid flows downhole, the valves will open, providing minimal interference. If fluid starts to move uphole, however, the valves close to prevent flow. 
         [0037]    Referring now to the figures,  FIGS. 1A and 1B  illustrate schematically and not to scale cross-sectional views of a prior art flapper check valve useful in the invention positioned in a CT. Illustrated in  FIG. 1A  is an open flapper check valve comprised of an insert  4  and movable flapper  6 . Insert  4  has an opening  1  allowing fluid to pass through the check valve and out through a second opening  3 . Insert  4  is positioned inside a CT wall  2 .  FIG. 1B  illustrates a closed check valve, for example when fluid attempts to reverse flow from opening  3  to opening  1 . 
         [0038]      FIGS. 2A and 2B  are schematic cross-sectional views of a prior art dart valve useful in the invention positioned in a CT. (The same numerals are used throughout the drawing figures for the same parts unless otherwise indicated.) Illustrated in  FIG. 2A  is a coiled tubing wall  2  having a first, relatively narrow opening  8 , and a second, relatively wider opening  3 . Higher pressure fluid entering through opening  8  forces a dart  10  and its supports  12  and  14  to press down on a spring  18  in a channel  16 , allowing fluid to flow through openings in support  12  and an opening  20  in support  14  and out through opening  3 .  FIG. 2B  illustrates the close position, wherein spring  18  has sufficient force to overcome the fluid pressure entering through opening  8  and force dart  10  to seat and close opening  8 . Higher pressure fluid entering opening  3  will also tend to force dart  10  to seat and close opening  8 . 
         [0039]    There are many varieties of check valves. Any and all known check valves and methods of using them are foreseeable functional equivalents and considered within the invention. One feature of the inventive apparatus and methods comprises a mechanical flow control system that only allows flow downhole through the tool, but that also can be overridden in the event that reverse circulation is desired. In order for the system to be safe, the override may be initiated and actuated from the well surface, or, in the absence of mechanical control from the well surface, locally initiated and actuated at the tool. If locally initiated and actuated, apparatus and methods of the invention may include a power source at the tool, so that the tool can shift to a safe position if communication is lost with surface. The type and capacity of the power source will vary depending on the actuation method used. 
         [0040]      FIG. 3  is a schematic cross-sectional view of one possible hydraulic system  30  useful in apparatus and methods of the invention. System  30  may use pressure developed by, for example, a pump, to store hydraulic pressure in a high pressure chamber  42  that overrides closed check valves, such as a dart valve  40 . The hydraulic pressure is released with a solenoid  44  that may be controlled by a downhole microprocessor (not shown). Solenoid  44 , releases pressure if instructed to do so from the well surface, or, if communication with the surface is lost, by actuating a check valve using a local power source such as a battery. The main components of embodiment  30  are illustrated schematically in  FIG. 3 . In its up position, a pressure lock piston  32 , forced up by a spring  34 , allows hydraulic fluid to flow freely into a compensation chamber  52 , so that there is no pressure differential across a check valve, which may be a ball  46  and spring  48  combination. In its down position, pressure lock piston  32  only allows flow across check valve  46 / 48  in one direction, from compensation chamber  52  into high pressure chamber  42 . Pressure lock piston  32  is normally forced up by spring  34 . When the hydraulic fluid pressure above pressure lock piston  32  is higher than the annulus (outside the tool) pressure below the piston (depicted as a low pressure chamber  36 ), spring  34  can be overridden and pressure lock piston  32  will move down. When a pressure differential is seen across check valve assembly  46 / 48 , solenoid  44  is activated, causing its actuator to move toward ball  46  to roll ball  46  off its seat and release the pressure. A compensating piston  50  provides an adequate supply of hydraulic fluid for the system. Compensating piston  50  allows for direct pressure transfer from the tool ID (represented as a chamber  38 ) above dart valve  40  to the hydraulic fluid. 
         [0041]    The basic operation of the hydraulic system of  FIG. 3  is illustrated schematically in  FIGS. 3A-3D , and its implementation into a tool or apparatus of the invention is illustrated schematically in  FIGS. 4A-4C .  FIGS. 3A ,  3 B,  3 C, and  3 D are schematic cross-sectional views of the hydraulic system of  FIG. 3  in different modes of operation. In  FIG. 3A  there is a low flow across dart valve  40 , and pressure lock piston  32  is in an intermediate position, balance by action of spring  34 , and pressure in tool  38  caused by pumping and pressure in annulus  36 . Solenoid  44  is deactivated to retract its actuator, and there is no pressure differential over check valve  46 / 48  (spring  48  is holding ball  46  against its seat). In  FIG. 3B , dart valve  40  continues to open as flow increases across it, and pressure lock piston  32  seats, compressing spring  34 . Note that the differential pressure that charges the hydraulic system need not be limited to that created by flowing across the dart valve and can be increased, for example, by adding a flow restriction (such as an orifice) below the dart valve. Compensating piston  50  moves upward, and some hydraulic fluid is allowed to enter high pressure chamber  42  by unseating ball  46 . In  FIG. 3C , compensating piston  50  is at its maximum travel upward, ball  46  seats, storing high pressure hydraulic fluid in high pressure chamber  42 . When a pressure differential is seen across check valve assembly  46 / 48 , solenoid  44  may be activated, either remotely or locally, allowing its actuator to extend to roll ball  46  off its seat and release the pressure, as depicted in  FIG. 3D . If all communication is lost to the tool, solenoid  44  is activated locally, and its actuator extends to push ball  46  off of its seat. 
         [0042]      FIGS. 4A ,  4 B, and  4 C are schematic cross-sectional views of a first apparatus embodiment of the invention in different modes of operation. Illustrated are coiled tubing wall  2 , an engineered section  2   a  of coiled tubing wall  2 , and a hydraulic system as previously described in reference to  FIGS. 3A-3D  installed in engineered section  2   a.  Engineered section  2   a  may either be formed in the coiled tubing wall itself during fabrication of the coiled tubing, or comprise a piece retrofitted into coiled tubing  2 . An opening  36  in CT wall  2  allows fluid communication with the annulus formed between wall  2  and the inside diameter of a well bore or well casing (not shown).  FIG. 4A  depicts the normal flow mode, where fluid traverses through CT opening at  1 , in the direction of the arrow, through an opening  8  and channel in an upper dart valve member  41 , past dart  10 , through a sleeve  54 , and finally past a flapper  6  of a flapper-style check valve. 
         [0043]    Because of the nature of dart valve  40 , a minimum pressure differential is necessary in order to flow across the valve.  FIGS. 3A-3D  show that this pressure differential charges the hydraulic system by creating a high pressure zone  42  above the valve and a low pressure zone below. Note that the differential pressure that charges the hydraulic system need not be limited to that created by flowing across the dart valve and can be increased, for example, by adding a flow restriction (such as an orifice) below the dart valve. The pressure differential begins to move compensating piston  50  to allow oil to flow above and shift dart valve  40  and flapper check valve. Also, the differential begins to move pressure lock piston  32  to its locked position. As the flow rate increases, as shown in  FIG. 4B , pressure lock piston  32  continues to move down until the piston lands on a seat that prevents further movement. Just before pressure lock piston  32  seats, a seal takes place that prevents flow of oil around the piston. Additional oil flow due to added flow rate and greater pressure drop will now occur across the hydraulic check valve,  46 / 48 . If flow stops after pressure lock piston  32  seats, pressure lock piston  32  will stay seated and hydraulic check valve  46 / 48  will prevent the charged oil from returning to compensation chamber  52 . Consequently, the closed volume of oil in high pressure chamber  42 , a passage  45 , and annular chamber  47  above the dart valve will force it in the down position, which also forces the flapper check valve  6  open with a push sleeve  54 . Once the system is charged and the pressure locked, flow can take place in both directions (as indicated by the double-headed arrow in  FIG. 4C ) across the flapper check valve and dart valve. When reverse circulation is completed, solenoid  44  is actuated to move ball  46  of the hydraulic check valve off its seat. In doing so, stored pressure in high pressure chamber  42  is released. The system returns to its original position, and flapper check valve  6  and dart  10  are returned to their normal position that prevents uphole flow. 
         [0044]    Apparatus of the invention may be powered locally by battery, fuel cell, or other local power source. Apparatus of the invention may include a two-way communication link to the surface, which may be a fiber optic line, wire line, or wireless, that provides two-way communication that makes the valve operation easier and safer. For example, a position sensor may be used to signal to surface whether a dart of a dart valve is in the up or down position, or a flapper of a flapper-style check valve. The operator may then be confident that the valve is open before reverse circulating, and the operator may stop reversing flow if the valve closes inadvertently. Apparatus and methods of the invention may also employ a failsafe signal line from surface to downhole. If present, the operator may fire a light source to the tool if reversing mode is desired. If the operator decides to stop reversing, or if the signal line is damaged or broken, the failsafe light source is removed. When this is detected at the tool, the tool automatically releases the hydraulic pressure in high pressure chamber  42  and returns the system to a safe position. In other words, even if the communications link is broken and the operator cannot pump or manipulate the CT (e.g. parted CT), the tool will still return to a safe position and prevent uphole flow of well fluids. This feature provides a benefit over known reversing valves, which require either pumping or CT manipulation to return to a safe mode. 
         [0045]    Apparatus of the invention may be described as intrinsically safe. In other words, if communication and control from surface are lost, apparatus of the invention return to safe mode and prevent uphole flow. Certain embodiments may use only one solenoid to operate a hydraulic system; in these embodiments, the apparatus is charged by a pressure drop across the dart valve. Other actuation arrangements are possible, however, that also return to a safe mode in the absence of intervention from surface. Two examples of alternate actuation methods are described below. These are presented as an overall picture of the types of actuators and actuation methods available and should only be considered as representative non-limiting examples. 
         [0046]    A motor may be used that produces a linear stroke to move the tool between conventional and reversing positions. A motor  62  might be packaged in tools of the invention as illustrated in embodiments  60  and  600  of  FIGS. 5 and 7 , respectively. Motor  62  may be adapted to have a linear motion drive shaft  63  attached to a piston head  65  of a movable valve gate  66 . An annulus bypass piston  67  is adapted to move into and out of a flow bypass chamber  69 , as depicted in  FIG. 7 . Note that an oil compensation system  64  may be used to protect and lubricate the motor, gears, and other mechanical parts  63 ,  64 ,  65 ,  66 , and  67 . Alternatively, these parts may be comprised of frictionless coatings. As illustrated in embodiment  600  of  FIG. 7 , as motor  62  is activated by an operator, it moves shaft  63 , piston head  65 , valve gate  66 , and annulus bypass piston  67  down, effectively closing a bypass formed by opening  36 , chamber  69 , and a bypass conduit  74 . During a reverse flow operation, since the pressure in the annulus is greater than the pressure in coiled tubing  2 , flappers  6   a  and  6   b  will close and restrict flow through the flappers. However, the described bypass, referred to as an annular bypass, allows a reverse cleaning procedure, as debris will flow through opening  36 , chamber  69 , bypass conduit  74 , and CT main flow conduit  1 . When it is desired to stop reverse flow, or power is lost to the tool, motor  62  is energized by a back-up power source (not illustrated), forcing annulus bypass piston  67  down, blocking any flow from the annulus through opening  36 , chamber  69 , bypass conduit  74 , and upward through CT main flow conduit  1 . 
         [0047]    As one alternative annular bypass apparatus and method, apparatus and methods of the invention may comprise two or more solenoids to actuate the reversing tool, as illustrated schematically in embodiments  70  and  700  of  FIGS. 6 and 8 , respectively. A first solenoid,  72 , may selectively close the flapper of check valve  6  to create a high pressure differential and charge the hydraulic system high pressure chamber  42 , as illustrated conceptually  FIGS. 6 and 8 .  FIG. 8  illustrates schematically how a dual solenoid arrangement could be used in conjunction with a hydraulic system. Second solenoid  44  may be adapted to release the stored hydraulic pressure, as previously described, while first solenoid  72 , in deactivated state as illustrated in  FIGS. 6 and 8 , selectively closes check valve  6  to charge the hydraulic system and allow reverse flow (upward) of well debris and fluids. When it is desired to stop reverse flow, or power is lost to the tool, second solenoid  44  is energized by a back-up power source, releasing the stored pressure and returning the system to a safe mode. 
         [0048]    While the annular bypass apparatus and method embodiments have been described as using a motor or dual solenoid system to operate the reversing tools of the invention, the invention is not so limited. Any component or collection of components that function to allow selectively opening and closing the path to the annulus may be employed. When the path to the annulus is open, and pressure in the annulus is greater than pressure in the CT, fluid and any solid debris may bypass the check valves and flow up the CT. 
         [0049]    The motor and dual solenoid arrangements may be used in inline bypass arrangements as illustrated in embodiments  601  and  701  in  FIGS. 9 and 10 , respectively, in a manner similar to the annulus bypass apparatus described in reference to  FIGS. 7 and 8 . However, for inline bypass apparatus, the uphole flow does not enter the tool directly from the annulus, but rather travels up the tool from within through a second CT flow channel  76 , as indicated by the arrows in  FIGS. 9 and 10 . Otherwise, apparatus of the invention including inline bypasses of  FIGS. 9 and 10  operate similarly in concept to the annulus bypass embodiments of  FIGS. 7 and 8 . 
         [0050]      FIGS. 11 and 12  illustrate how the two actuation arrangements may be used to directly override two flapper-style check valves, allowing uphole flow. The assembly illustrated schematically in  FIG. 11 , may include a motor  62 , motor shaft  63 , and movable valve gate  66 , which now moves dual flapper actuators  77  and  79 , each having a notch  78  and  80 , respectively. Movement up of shaft  63 , gate  66 , actuators  77  and  79 , and notches  78  and  80  mechanically opens flappers  6   a  and  6   b,  allowing reverse flow. The assembly in  FIG. 12  uses dual solenoids  72  and  44  to charge the hydraulic system and release the pressure. When the hydraulic system is charged, the hydraulic pressure in conduits  45 ,  45   a,  and  45   b  shifts pistons  81  and  82 , mechanically opening flappers  6   a  and  6   b . When it is desired to stop reverse flow, or power or communication is lost, solenoid  44  is activated, releasing hydraulic pressure in conduits  45 ,  45   a,  and  45   b,  allowing flappers  6   a  and  6   b  to close in safe position. 
         [0051]    Two other embodiments  603  and  703  that may utilize either a motor (embodiment  603 ) or a dual-solenoid (embodiment  703 ) actuation system are illustrated schematically in  FIGS. 13 and 14 . Both actuation systems utilize stored hydraulic pressure to shift a sleeve that overrides two flapper check valves (only one shown due to space constraints). For the motor assembly illustrated in  FIG. 13 , motor  62  may have a first motor position that closes hydraulic flapper valve  6  and charges hydraulic system  64  and  91 , moving a push sleeve  84  down against spring pressure by a push sleeve spring  88  against a flange  85  connected to sleeve  84 , until a locking pin  93  pops into place on push sleeve  84 . Push sleeve  84  may be guided by a bearing  86 , and a distal end  89  of push sleeve  84  pushes open flappers  6   a  and  6   b  (the latter not shown). Then, by pulling up with motor  62  to a second motor position, locking pin  93  releases, and push sleeve  84  returns to its starting position by action of push sleeve spring  88 , and flappers  6   a  and  6   b  close. The system in  FIG. 14  may use dual solenoids  72  and  44  to store and release hydraulic pressure in high pressure chamber  42  and conduit  45 . When charged, the hydraulic system holds push sleeve  84  and push sleeve flange  85  down, overriding push sleeve spring  88  and causing flapper check valves  6   a  and  6   b  (the latter not shown due to space limitations) down. When upper solenoid  44  releases the pressure, push sleeve  84  returns to its original position. In both embodiments  603  and  703 , a passageway  90  may be provided to equalize pressure and provide lubricant. 
         [0052]    An optional feature of apparatus of the invention is one or more sensors located at the tool to detect the presence of hydrocarbons (or other chemicals of interest) in the fluid traversing up CT main passage  2  during a reverse flow procedure. The chemical indicator may communicate its signal to the surface over a fiber optic line, wire line, wireless transmission, and the like. When a certain chemical is detected that would present a safety hazard if allowed to reach surface (such as oil or gas), the reversing system is returned to its safe position, long before the chemical creates a problem. 
         [0053]    An overall operating process logic diagram for using apparatus of the invention is illustrated in  FIG. 15 . This operational flow diagram may include chemical detection at the tool.  FIG. 15  illustrates not only how easy the system is to operate, but also how the two main safety risks, lost tool/surface communication and hydrocarbon (for example) entry into the tool, are mitigated. In the first box,  101 , a pump providing hydraulic pressure is set at minimum rate and recorded as QSET. A microprocessor, or the operator, asks if the valve is fully open, represented by question box  102 . If yes, a reverse circulate flow procedure is followed, as indicated at  103 . Continuing this line of logic, the method may ask, at  104 , if chemical is detected. If yes, a chemical handling procedure s followed, represented buy box  105 . If no chemical is detected, the method may ask if the signal is lost from the surface at  106 . If yes, for safe operation pressure is released at  108 , and if no, the process asks if reversing is completing ay  107 . If reversing is complete, pressure is released at  108  by firing a solenoid. If reversing is not complete, the process and apparatus continue to follow the reverse circulation procedure indicated at box  103 . After pressure is released when reversing is complete, the logic asks if the valve is fully closed. If not, the solenoid is fired again until reverse flow stops. The apparatus repeats the procedure, as indicated by box  110 . Returning to box  102 , if the valve is not fully opened using the QSET pump pressure, the pump rate is increased, as indicated at box  111 . The logic asks if the pump maximum flow rate, QMAX, has been reached, at  112 . If yes, the pump is stopped and the conclusion is reached that there must be a problem at the tool, indicated at box  113 . If QMAX has not been reached, the logic again asks if the valve is now fully open, as indicated at box  114 . If yes, the pump rate at which the valve is fully open is recorded as QSET at  115 , and the pump is stopped at  116 . Those of skill in the art will recognized many options, and possible and foreseeable variations in the logic, and these variations are considered within the scope of the invention. 
         [0054]    A typical use of this invention will be in situation when a normal clean out using coiled tubing is or will become more difficult as a well bore becomes too large in diameter, causing the annulus to be too wide. In these situations, forcing cleaning fluid down the CT will not normally produce high enough rate in the annulus to force the fluid and debris out of the well bore. Apparatus of the invention may then be employed to “reverse the flow”. Cleaning fluids are pumped down the annulus, and one of the apparatus and method embodiments of the invention employed to reverse flow upwards through the CT. 
         [0055]    Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, no clauses are intended to be in the means-plus-function format allowed by 35 U.S.C. §112, paragraph 6 unless “means for” is explicitly recited together with an associated function. “Means for” clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.

Summary:
Apparatus and methods for selectively and safely reversing flow in coiled tubing used for wellbore cleanouts are disclosed. One apparatus includes a section of coiled tubing having a main flow channel, at least two flow-preventing valves in the section of coiled tubing, each adapted to close the main flow channel upon attempted flow reversal; and at least one actuator adapted to deter closing of the flow-preventing valves. This abstract allows a searcher or other reader to quickly ascertain the subject matter of the disclosure. It will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).