Abstract:
A wellbore fluid recovery system and method is disclosed for recovering a column of wellbore fluid within a stand of pipe when breaking out joints of a wellbore tubular string. The system comprises a container that can be mounted to seal around the joint. The container is preferably connected through a first valve to a receiving tank to which a vacuum may be applied. A vacuum tank may preferably be provided to assist in producing the vacuum in the receiving tank and a second valve preferably connects between the receiving tank and the vacuum tank. A third valve may be provided for controlling flow from the receiving tank to a storage tank for wellbore fluid. Prior to breaking the joint, a vacuum is preferably applied to the receiving tank. The first valve may then be opened to remove the fluid from the joint that is captured by the container in response to the vacuum in the receiving tank. Subsequently, the third valve is opened to permit drainage between the receiving tank and the storage tank. The first and third valves may then be closed and the second valve may be opened for producing a vacuum in the receiving tank. A vacuum source may be used to increase the vacuum in the receiving tank further as necessary. The second valve may then be closed and the system is ready to operate as described above to receive fluid from the next joint.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to drilling and completion fluid recovery and, more specifically, to a system for preventing wellbore fluids from being spilled when the threaded connections between the joints of the wellbore tubulars are disconnected, while being tripped out of the wellbore.  
           [0003]    2. Description of the Background  
           [0004]    During what is sometimes called a “wet” trip, a release of drilling fluid may occur with each of a large number of drill pipe connections that are broken. As the drill pipe string is being removed from the well, for example to substitute a new drilling bit for a worn drilling bit, the drilling mud that may remain in the string can create considerable problems. Each stand of drill pipe may be approximately ninety feet long in accordance with the drilling rig size. Depending on well conditions, the pipe which is removed may therefore contain up to a ninety-foot column of drilling fluid therein. Although variable based on the size of the drill pipe, the volume of fluid in a ninety-foot column may be in the range of as much as one hundred fifty gallons. When a threaded joint between the stand of drill pipe and the drill string is disconnected, this column of mud is released to flow from the length of the drill pipe. This release of wellbore fluids may typically occur many times during a “wet” trip.  
           [0005]    Drilling and completion fluids which include fluids such as weighted mud, oil-based fluids, water-based muds and the like are often quite expensive and may frequently cost more than one million dollars per well. Loss of such fluids during the numerous pipe trips made per well can therefore be quite costly as the fluids will need to be replaced. Moreover, the loss of such fluids can also create pollution which is highly undesirable. As well, the fluids may create an unusually slippery rig floor and surroundings so as to cause safety problems by increasing the likelihood of accidents to operators working on the rig floor.  
           [0006]    The above problems are well known in the oil industry and therefore many efforts have been made in past years to limit spillage. One exemplary prior art system for a drilling mud container apparatus is disclosed in U.S. Pat. No. 5,295,536, issued Mar. 22, 1994, to Robert E. Bode, and is incorporated herein by reference. The drilling mud container apparatus provides a container for preventing spilling of drilling mud onto the rig floor to thereby save the mud for later reuse. The invention includes a diametrically split and hinged barrel having a fixed lower seal assembly and a movable upper seal assembly which engage the outer wall of the drill pipe respectively below and above a joint connection that is to be unthreaded. Upon disconnection of the joint and upward movement of the drill pipe, the upper seal moves upward with the pipe to eliminate wear which otherwise would result in seal and mud leakage. The container includes a large drain port and is adapted to be connected to a suitable hose which leads to a mud pit or tank.  
           [0007]    However, several significant problems still exist with prior art fluid recovery systems. One problem relates to the amount of time required for the recovery system to operate. Draining large amounts of fluid as each connection is broken considerably increases the overall effective time required to break each connection and therefore significantly increases the time required for tripping the drilling string out of the wellbore. Therefore, the associated time costs of wet trips may also significantly increase the cost of drilling the well. As another factor, unless considerable time is allowed for drainage and dripping, depending on the viscosities and flow rates of the fluid, size and length of pipes, drilling fluid losses may still occur that are greater than permissible under governmental regulations even though the losses are greatly reduced. Another problem is related to the size of the container that must be secured around the pipe joint. To avoid the need for numerous different size containers related to the expected volume of fluid and size of pipe, a single container size with removable seals designed for each pipe size is generally constructed to be large enough in volume to handle the largest flows anticipated. However, due to this large size, the container can be awkward to work with thereby resulting in more loss of time as well as the inconvenience and hazards of working with unwieldy and bulky equipment.  
           [0008]    Consequently, it would be desirable to further improve prior art drilling and completion fluid recovery prior art systems. It would be highly desirable to reduce loss of drilling fluid even more than has been possible in the past, and to do so in much less time. It would also be desirable to reduce the size of the container used in prior art systems while still retaining the ability to handle the maximum possible fluid flow as the pipe connection is broken. Thus, it would be desirable to save the considerable cost due to time loss while even further reducing any loss of expensive and possibly environmentally harmful drilling fluids. It is always desirable to further improve safety conditions. Those skilled in the art have therefore long sought and will greatly appreciate the present invention which addresses these and other problems.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention was designed to provide more efficient operation to thereby save time and reduce drilling costs, significantly improve speed of breaking pipe joints during a wet trip, permit increased automation to reduce required manpower, improve safety, and to reduce any possible well fluid loss into the environment.  
           [0010]    Therefore, it is an object of the present invention to provide an improved wellbore fluid recovery system.  
           [0011]    Another object of the present invention is to have the ability to reduce the time required for breaking joints during a wet trip.  
           [0012]    Yet another object of the present invention is to reduce the size of the container positioned around the pipe joint to catch fluid when the joint is broken.  
           [0013]    An advantage of the present invention is improved rig safety.  
           [0014]    Another advantage of the present invention is faster operation.  
           [0015]    Yet another advantage is lower costs.  
           [0016]    These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims.  
           [0017]    Therefore, the present invention provides for a wellbore fluid recovery system for recovering wellbore fluid when breaking one or more joints of wellbore tubulars comprising elements such as a container mountable around each of the one or more joints of the wellbore tubulars, a receiving tank, a first conduit between the container and the receiving tank, and a vacuum source operable for producing a vacuum within the receiving tank.  
           [0018]    A first valve may preferably be provided for controlling flow through the first conduit. A vacuum tank is included in a preferred embodiment of the invention and the vacuum source may be adapted for producing a vacuum in the vacuum tank. A second conduit between the vacuum tank and the receiving tank is preferably provided with a second valve for controlling flow through the second conduit. A wellbore fluid storage tank, such as a trip tank, is connected to the receiving tank by a third conduit. A third valve controls flow through the third conduit.  
           [0019]    In one preferred embodiment, the container for attachment around the pipe joint has a container volume less than a volume of the column of wellbore fluid to thereby provide a more compact container.  
           [0020]    The method of the invention may preferably comprise steps such as the steps of placing the container around the joint, unscrewing the joint, applying the vacuum to the container, and collecting the fluid in the receiving tank. The step of applying the vacuum may further comprise opening the first valve to permit fluid communication between the receiving tank and the container. Prior to opening the first valve, the vacuum is preferably produced in the receiving tank. In a preferred embodiment, the vacuum is first produced in the vacuum tank and then the second valve between the vacuum tank and the receiving tank is opened. Prior to operation, all three valves are closed. After fluid is collected in the receiving tank, the third valve is opened to drain the wellbore fluid into a storage tank.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a schematic view of a system in accord with an embodiment of the present invention prior to breaking of the wellbore tubular joint;  
         [0022]    [0022]FIG. 2 is a schematic view of the system of FIG. 1, when the wellbore tubular joint is broken and fluid is drawn by vacuum into a receiving tank in accord with an embodiment of the present invention;  
         [0023]    [0023]FIG. 3 is a schematic view of the system of FIG. 2, after fluid has been drawn into the receiving tank and flows therefrom by gravity into a rig site well fluid reservoir as the drill pipe is racked in the derrick; and  
         [0024]    [0024]FIG. 4 is a schematic view of the system of FIG. 3, after fluid has flowed out of the receiving tank and a vacuum is again produced in the receiving tank to place thereby the system in the status shown in FIG. 1. 
     
    
       [0025]    While the present invention will be described in connection with presently preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents included within the spirit of the invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Referring now to the drawings which show operation of fluid recovery system  10  in accord with the present invention, and more particularly to FIG. 1, there is shown drilling recovery system  10  prepared for receiving wellbore fluids such as drilling or completion fluids as wellbore tubular threaded connection  12  is broken apart in a manner known by those skilled in the art. Thus, wellbore pipe string  14 , such as a drill pipe string, completion string, production string, or other wellbore tubular string, is being pulled from the wellbore through rig floor  16 . Upper stand of pipe  16  may typically include about three drill pipes threadably connected together. Each drill pipe is typically about thirty feet long. The drilling rig height normally allows multiple pipes to be contained in each stand so that, for instance, only every third pipe connection needs to be disconnected. Each stand is lifted, set aside, and stacked upright on one side of the derrick until drill pipe string  14  is to be run back into the well. By working with stands of multiple pipes rather than individual pipes, a great deal of time is saved.  
         [0027]    Depending on the hydraulics of the wellbore, it may be that the annular pressure outside the drill string  14  is greater than the pressure within the drill string. This may occur, for instance, due to heavy cuttings in the wellbore fluid, U-tube effects, and the like. When pulling out the drill string with a bit having small or clogged jets, nozzles, or water ways, the mud may be trapped in the drill string or not have time to drain during the trip out of the hole. Thus, it is well known that when connection  12  is broken, approximately ninety feet of mud column inside drill stand  16  may be dumped out of the bottom end of stand  16 . Prior to breaking connection  12 , slips  19  engage drill string  14  to prevent drill string  14  from dropping into the wellbore when connection  12  is released. The connection may then be initially slightly rotated a few degrees by applying a high initial breaking torque with powered tongs of which there are many types. Prior to spinning stand  16  with respect to wellbore string  14  to thereby completely unscrew connection  12 , and perhaps prior to initial breaking of the connection with power tongs as discussed above, fluid recovery container  18  is preferably placed around connection  12  in a manner known to those of skill in the art. Fluid recovery container  18  will preferably include upper and lower seals such as upper seal  20  above joint  12  and lower seal  22  below joint  12 . The seals may be of various types such as sliding seals and the like as are known in the prior art.  
         [0028]    It will be understood that such terms as “up,” “down,” “vertical” and the like are made with reference to the drawings and/or the earth and that the devices may not be arranged in such positions at all times depending on variations in operation, transportation, and the like. As well, the drawings are intended to describe the concepts of the invention so that the presently preferred embodiments of the invention will be plainly disclosed to one of skill in the art but are not intended to be manufacturing level drawings or renditions of final products and may include simplified conceptual views as desired for easier and quicker understanding or explanation of the invention. As well, the relative size of the components may be greatly different from that shown, e.g., a wellbore fluid storage tank such as trip tank  36 , discussed below, may typically be much larger than receiving tank  30 .  
         [0029]    Outlet  24  is provided from container  18 , and is connected by hose or pipe  26 , through valve  28  to recovery tank  30 . Valve  28  may be of many types including but not limited to rotatable element valves such as ball valves, plug valves, butterfly valves, and the like, sliding element valves such as gate valves and the like, pivotal element valves such as flapper valves, plunger and seat valves, and any other suitable valves. Thus, valve  28  may be any type of valve so long as it is suitable to provide the function of the system as discussed hereinafter. Valve  28  may be manual or automatic, hydraulically operated, air operated, biased to one position as desired, or have other controls and the like. Again, any variety or combination of operating features may be used for controlling valve  28  so long as such operational features are suitable to provide the function of the system as discussed herein. As well, valve  28  may comprise more than one valve, more than one valve element, single or multiple valve controllers or actuators and the like, and/or more than one conduit such as conduit  26 .  
         [0030]    Recovery tank  30  has one or more outlets such as outlet  32  with one or more valves such as valve  34  that leads to rig reservoir tank  36  for storing wellbore fluids such as a trip tank, mud pit or tank, and/or other fluid tank in which it is desirable to store the recovered wellbore fluids. Outlet  32  may preferably be located on or near bottom section  38  of fluid recovery tank  30  so as to facilitate gravity feed or flow of fluid from recovery tank  30  to reservoir tank  36 . Valve  34  could also be of many types and could be operated by many methods and controls some but not all of which were mentioned above in connection with valve  28 . Valve  34  may or may not be the same type of valve or valves as valve  28 .  
         [0031]    Recovery tank  30  also connects to vacuum tank  40  through one or more outlets such as outlet  42  through which fluid flow is controlled by one or more valves such as valve  44 . Valve  44 , like valves  34  and  28  discussed above may be of many different types with many different types of controls. Vacuum tank  40  includes, in a presently preferred embodiment, one or more vacuum pumps such as vacuum pump  46  for producing a vacuum within vacuum tank  40 . Outlet  42  may preferably be located near an upper or top section  48  of reservoir tank  30  to reduce the likelihood of liquid flow therethrough.  
         [0032]    In the sequence of operation of a preferred embodiment of the invention as illustrated by FIG. 1, valves  28 ,  34 , and  44  are initially closed. A vacuum has been formed in receiving tank  30 , as will be discussed subsequently. Because all outlets  26 ,  32 , and  42  are closed by their respective valves  28 ,  34 , and  44 , the vacuum is maintained within receiving tank  30 . Receiving tank  30  is therefore sufficiently air tight for this purpose. Receiving tank  30  has sufficient volume to receive the entire column  50  of wellbore fluid in stand  16  and so may preferably be greater than one hundred fifty gallons or any suitable size for quick filling thereof.  
         [0033]    In FIG. 2, stand  16  has been rotated such as with a spinner, or other pipe rotating means which may be of many different types typically but perhaps not always in the counterclockwise direction indicated by arrow  52  to thereby unscrew joint  12  to break apart pin  54  from box member  56 . Therefore wellbore fluid in column  50  flows out into container  18  which, as stated above, is preferably sealed around pipe or stand  16  with seats such as seal  20  and  22 . Use of the present invention reduces the likelihood of leakage of seals  20  and  22  due to the vacuum applied to container  18  as discussed herein.  
         [0034]    During this time period, or shortly before or after the stand is spun to disconnect joint  12 , valve  28  is preferably opened. Valve  34  and preferably valve  44  may remain closed at this time as indicated in FIG. 2. The vacuum within receiving tank  30  creates a suction force on the wellbore fluid in stand  16  due to the differential pressure between the atmospheric pressure and vacuum inside receiving tank  30 . This suction force, in addition to the gravitational force, acts on the wellbore fluid in stand  16  to cause the wellbore fluid to flow more quickly into receiving tank  30  where the fluid is accumulated as indicated at  57 . The greater the vacuum, the faster fluid will flow. As well, increased hose size of conduit  26  or multiple hoses will enhance fluid flow. Due to the vacuum, the fluid flow will continue to flow from container  18  much faster than if left to flow purely by gravity. As well, less fluid will be left within container  18  and stand  16  in a shorter period of time. Thus, expensive rig time is saved as compared to the prior art. As well, because container  18  will be empty quickly due to opening of valve  28 , container  18  can be much smaller and more convenient to work with thereby again saving expensive rig time and also improving rig safety conditions. The smaller interior surface area of container  18  also reduces the amount of possible fluid loss and drainage time. Thus, all or practically all wellbore fluid is drawn by the vacuum in receiving tank  30  until the vacuum is exhausted and the pressure within receiving tank  30  preferably reaches atmospheric pressure.  
         [0035]    Receiving tank  30  is then drained as indicated in FIG. 3. During drainage of receiving tank  30  by opening of valve  34 , valve  44  to vacuum tank  40  preferably remains closed. Due to the present invention, container  18  may be more quickly removed from around pin  54  of stand  16  and box  56  of the remaining wellbore tubular string  16 . Thus as also indicated in FIG. 3, container  18  is removed to allow stacking of stand  16 . At this time, valve  34  is left open to allow fluid to drain by gravity into any desired tank  36  for the rig fluid system such as a trip tank. As the rig is busy stacking stand  16  and getting ready to pull another stand from wellbore tubular string  14 , there is time to permit gravity drainage of system  10  that does not interfere or slow down rig operation as occurs when gravity drainage is used to drain a typically larger container  18 . Valve  28  may also preferably be left open during this time to enhance drainage into tank  36  from receiving tank  30 .  
         [0036]    [0036]FIG. 4 shows a presently preferred embodiment of the next stage of operation of system  10 . Valves  28  and  34  are closed. Valve  44  is opened. Vacuum tank  40  preferably already has a vacuum therein. After review of the present specification, one of skill in the art will understand there are different possible methods of operation and system  10  features to produce the vacuum in receiving tank  30 . For instance, depending on the size of vacuum tank  40  as compared to the size of receiving tank  30 , and the degree of vacuum in vacuum tank  40 , as compared to the desired amount of vacuum in receiving tank  30 , system  10  may, if desired, be designed such that the opening of valve  44  almost instantaneously places receiving tank  30  at the desired vacuum. In one embodiment, vacuum pump  46  could even be a smaller less expensive vacuum pump that runs for a longer time such as during the operation shown in FIG. 1, FIG. 2, and FIG. 3, to place vacuum tank  40  at a desired vacuum level. Alternatively, the vacuum in tank  40  may partially evacuate receiving tank  30  with some additional vacuum assist required from vacuum pump  46  which will be sized to produce the desired vacuum in tank  30  within a short time period as will be available without slowing normal rig time operation as the next pipe joint is being positioned by the rig. Vacuum pump  46  may be activated manually or automatically, such as for instance by a switch responsive to a reduced level of vacuum. After activation, depending on the desired arrangement of system  10 , vacuum pump  46  may continue to operate until the desired amount of vacuum is produced within receiving tank  30  and/or vacuum tank  40 . In yet another embodiment, vacuum pump  46  could be directly connected to tank  30  assuming the action of vacuum pump  46  or multiple vacuum pumps is sufficient to produce the desired amount of vacuum in receiving tank  30  within the time allowed for stacking stand  16  and pulling up a new stand for removal from wellbore tubular string  16  which may typically be in the range of 15-60 seconds. At that time, valve  44  is closed again. Pump  46  may be turned off or, if desired, pump  46  may continue to reduce the pressure in vacuum tank  40  to a level less than that of receiving tank  30 . The sequence of replenishing the vacuum, e.g., reduced pressure with respect to atmospheric pressure, within receiving tank  30  may preferably take place as wellbore tubular string  14 , such as a drill string or production string or other tubular string, is being lifted by the rig blocks (not shown). When wellbore tubular string  14  is raised to the proper position, then slips  19  will be set, container  18  will be positioned around the next joint to be broken or which is already partially broken, and system  10  will again be in the situation as indicated in FIG. 1. Thus, FIGS.  1 - 4  illustrates a sequence that is repeated for each connection  12  that is broken.  
         [0037]    It will be understood from the discussion above that various changes and alternatives may be used that are within the spirit of the invention. For instance, system  10  of the present invention may be combined with automatic pipe breaking assemblies so as to be fully automated. System  10  may also be combined and/or operated in conjunction with other devices such as pipe handling or racking tools. A control system may be used to completely automate operation of valves  28 ,  34 , and  44 , vacuum pump  46 , container  18 , and the like. Alternatively, the system could be manually operated or some parts could be automatic and others manual. Various sensors such as fluid flow sensors, valve state sensors, fluid level indicators, pressure indicators, and the like could be used as part of a control system for fluid recovery system  10 . The supporting arm of container  18  could be attached to an automatic pipe breakout unit which unit may have two or more torque arms and/or power spinners. While a separate vacuum tank  40  is preferably used, vacuum pump  46  might also be attached directly to receiving tank  30  and/or other vacuum systems and arrangements may be made to apply a vacuum to container  18  and/or to produce and/or maintain a vacuum within receiving tank  30 . A two stage vacuum or multiple stage assist may be used whereby a second vacuum is applied to receiving tank  30  or container  18  either simultaneously or subsequent to that of system  10  as described hereinbefore.  
         [0038]    While system  10  is shown as being constructed with most elements located below rig floor  16  where tanks  30  and  40  are conveniently out of the way, fluid recovery system could also contain one or more tanks above the rig floor or positioned as is convenient for rig conditions.  
         [0039]    The foregoing disclosure and description of the invention is illustrative and explanatory thereof, and it will be appreciated by those skilled in the art, that various changes in the size, shape and materials, the use of mechanical equivalents, as well as in the details of the illustrated construction or combinations of features of the various elements may be made without departing from the spirit of the invention.