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BACKGROUND 
       [0001]    In many well applications, various well cementing operations are performed. To improve the integrity of the cement material, fiber products acting as fluid-loss reduction additives can be added to the cement slurry that is pumped downhole. The fiber products typically are added by hand or with toothed drums. However, such techniques can lead to uneven metering of the fiber products into the cement mix. Additionally, toothed drums and other field-improvised equipment can be inadequate due to insufficient delivery rate, lack of reliability, and lack of accuracy. 
         [0002]    Additionally, any equipment used to deliver fiber material into the cement mixing tank can present a problem with respect to height of the equipment. When equipment is mounted on top of a portable well servicing unit, for example, the equipment is susceptible to extending beyond the legal height requirements that must be met when transporting equipment over a highway system. 
       SUMMARY 
       [0003]    In general, a system and methodology is provided that facilitate well servicing operations, such as cementing operations. A hopper system is designed to introduce an additive into a cement mixing tank. The hopper system comprises a feeder and a hopper that delivers the additive into the feeder. The feeder, in turn, enables introduction of the additive into the cement mixing tank in a controlled manner. When the hopper system is used on a transportable cementing unit, the hopper system may be mounted on a cement mixing tank. In this type of application, the hopper also may be expandable to accommodate a greater amount of additive and contractible to facilitate transport. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
           [0005]      FIG. 1  is a schematic illustration of an embodiment of a transportable cementing unit; 
           [0006]      FIG. 2  is a schematic illustration similar to that of  FIG. 1  but showing the transportable cementing unit in an expanded configuration; 
           [0007]      FIG. 3  is an orthogonal view of one embodiment of a hopper in a contracted position; 
           [0008]      FIG. 4  is an orthogonal view of one embodiment of a hopper in an expanded position; 
           [0009]      FIG. 5  is an illustration of one example of a hopper system; 
           [0010]      FIG. 6  is another illustration of the hopper system illustrated in  FIG. 5 ; and 
           [0011]      FIG. 7  is an illustration of one example of a feeder that can be used in the hopper system illustrated in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill 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. 
         [0013]    The present disclosure relates to a system and methodology to facilitate well cementing operations. The system and methodology employ a hopper system that comprises a unique feeder to meter additives, e.g. dry additives, into a cement mixing tank. The additives are mixed into a cement slurry which can then be pumped downhole to perform a variety of well related cementing operations. The hopper system works well with additives having fibers, and other fibrous fluid-loss reduction agents. According to one embodiment, the feeder has a screw-type design of appropriate geometry and material selection to enable a precisely controlled metering rate and to improve reliability and accuracy with respect to the metering of fibrous fluid-loss reduction additives for well cementing work. 
         [0014]    Additionally, the hopper system may be designed to facilitate ease of operation at a well site while allowing transport of the hopper system when mounted to a transportable cementing unit. For example, the hopper system may be part of a well servicing system having a transportable cementing unit mounted on a truck or trailer for transport over public highway systems. In some embodiments, the hopper system is mounted on top of a cement mixing tank which forms part of the transportable cementing unit. In this embodiment, the hopper system comprises a hopper positioned above the feeder, and the hopper can be selectively expanded in capacity to, for example, hold one sack of additive, e.g. fiber additive, or another desired quantity of additive. The hopper also can be selectively contracted to reduce the height of the overall transportable cementing unit to ensure the overall transportable unit meets legal road height limits. The hopper may be extended during a well cementing operation and retracted after the operation for transport. 
         [0015]    Referring generally to  FIG. 1 , an embodiment of a transportable well servicing unit  20 , such as a transportable cementing unit, is illustrated. In this embodiment, the transportable cementing unit  20  may be part of a truck or trailer that enables transport along a public highway system. It should be noted that the transportable unit may comprise a variety of other components, systems and features to facilitate well cementing operations and other well servicing operations. However, relevant portions of transportable cementing unit  20  have been illustrated in  FIG. 1  to facilitate explanation of the present system and its operation in conducting well cementing operations. 
         [0016]    In the embodiment illustrated, transportable cementing unit  20  comprises a platform  22  that may be a trailer or truck bed designed to transport the cementing unit  20  over public highways and other types of roads. The transportable cementing unit  20  further comprises a cement mixing tank  24  and a hopper system  26  mounted on the cement mixing tank  24 . The cement mixing tank  24  is designed to mix a desired cement slurry that may be pumped downhole into a wellbore via a pumping system mounted on platform  22  or on a separate transportable platform. The cement slurry is pumped into the wellbore and delivered to specific regions of the wellbore to accomplish the planned cementing operation. 
         [0017]    The hopper system  26  may be used to deliver additives into cement mixing tank  24 . For example, dry additives may be added to the cement slurry to provide the cement slurry with characteristics that improve the quality of the cementing job. In a variety of applications, the additive comprises a fibrous fluid-loss reduction additive that substantially improves the functionality of the cement downhole. 
         [0018]    In the embodiment illustrated, hopper system  26  comprises a feeder  28  mounted, for example, directly above the cement mixing tank  24  to precisely meter additive into cement mixing tank  24 . The illustrated hopper system  26  also comprises a hopper  30  mounted on feeder  28 . For example, the hopper  30  may be mounted directly over feeder  28  to guide additive into an upper opening of the feeder  28 . The additive, e.g. a fibrous fluid-loss reduction additive, can be poured into an upper hopper opening  32 , and hopper  30  is designed to guide the additive to feeder  28 . 
         [0019]    Hopper  30  may be designed as an adjustable hopper that can be actuated between a contracted configuration, as illustrated in  FIG. 1 , and an expanded configuration, as illustrated in  FIG. 2 . Expansion of the hopper  30  increases the capacity of the hopper and enables loading of the hopper with a predetermined amount of additive material. For example, hopper  30  may be designed so that in its expanded configuration a standard bag of fiber based additive can be poured in its entirety into the hopper  30 . Additionally, the ability to contract hopper  30  decreases the height of the overall transportable cementing unit  20 , at least in the embodiments in which hopper system  26  is mounted on top of cement mixing tank  24 . The contracting or lowering of hopper  30  facilitates meeting the legal height requirements imposed on vehicles traveling on a variety of public highway systems. 
         [0020]    The expansion and contraction, e.g. raising and lowering, of hopper  30  can be accomplished automatically with an actuation system  34 . By way of example, actuation system  34  comprises a pressure system  36  that directs fluid under pressure to cylinders  38  which are mounted between a movable portion  40  of hopper  30  and a stationary portion  42 . Fluid is delivered from pressure system  36  to cylinders  38  and returned from cylinders  38  via pressure lines  44 . Additionally, a valve or valves  46  can be used to control the flow of pressure fluid and thus the actuation of cylinders  38 . In the illustrated example, cylinders  38  are dual acting cylinders to enable both the controlled expansion and contraction of hopper  30 . In a variety of specific applications, pressure system  36  comprises a pneumatic pressure system using air or other appropriate fluid to actuate pneumatic cylinders  38 . However, pressure system  36  also may be formed as a hydraulic pressure system. 
         [0021]    Transportable cementing unit  20  also may comprise a canopy system  48  to provide a covering during operation of hopper system  26  and cement mixing tank  24 . By way of example, canopy system  48  comprises a movable canopy  50  that can be raised to a working configuration, as illustrated in  FIG. 2 , or lowered to a transport configuration, as illustrated in  FIG. 1 . In the embodiment illustrated, canopy  50  is raised and lowered via cylinders  52  mounted between, for example, canopy  50  and cement mixing tank  24  or other suitable structure. Cylinders  52  may be powered by pressure system  36  and may comprise, for example, hydraulic or pneumatic cylinders. 
         [0022]    In an embodiment, pressure system  36  is a pneumatic pressure system coupled to hopper  30  via pressure lines  44  and to cylinders  52  of canopy system  48  via pressure lines  54 . The pressure lines  44  and  54  can be connected to a common valve  46  that enables actuation of both canopy system  48  and hopper system  26  by adjusting a single valve. For example, when the transportable cementing unit  20  is deployed at a well site and set up for a cementing operation, valve  46  can be opened to both raise canopy  50  and expand hopper  30 . Upon completion of the cementing operation, valve  46  can be reversed to move hopper  30  into the contracted configuration and canopy  50  into the lowered position for transport. The actuation may be timed so that the canopy rises before the hopper and lowers after the hopper is moved to its contracted configuration. 
         [0023]    Referring generally to  FIG. 3 , one embodiment of hopper  30  is illustrated. In this embodiment, hopper  30  is a pneumatically actuated hopper that may be actuated from the contracted configuration of  FIG. 3  to the expanded configuration of  FIG. 4  by two dual acting pneumatic cylinders  38 . The expansion and contraction are accomplished by forming the hopper as a telescopic hopper in which movable portion  40  is telescopically received in stationary portion  42 . The cylinders  38  extend between a flared portion  56  of the movable portion  40  and a base portion  58  of the stationary portion  42 . The dual acting cylinders  38  enable the controlled expansion and contraction of hopper  30  as portion  40  is moved telescopically outward and inward, respectively, with respect to stationary portion  42 . 
         [0024]    In the embodiment illustrated and in other embodiments of hopper  30 , a variety of alternate or additional components can be incorporated into the design. For example, one or more pressure gauges  60  may be deployed along the lines  44  to monitor pressure applied to cylinders  38 . Additionally, the hopper opening  32  may incorporate a grate  62  or other structure to break up the additive material as it is poured into hopper  30  through opening  32 . Additionally, hopper  30  may be formed from a variety of materials that provide suitable longevity and consistent actuation when used with the desired additive in a variety of well site environments. In an embodiment, movable portion  40  and stationary portion  42  are formed from stainless steel, however other materials and combinations of materials may be employed. 
         [0025]    As further illustrated in  FIG. 5 , the hopper  30  may be mounted directly over feeder  28  to create hopper system  26 . In this embodiment, feeder  28  comprises an inlet  64  which may be in the form of an upper opening positioned beneath hopper  30  to receive the additive directed through hopper  30 . The feeder  28  is designed to accurately meter the desired amount of additive at the desired rate into cement mixing tank  24 . 
         [0026]    In the embodiment illustrated, feeder  28  comprises a feeder body  66  containing at least one screw  68  for moving additive along feeder body  26  before discharging it into cement mixing tank  24 , as further illustrated in  FIGS. 6 and 7 . The at least one screw  68  may comprise a constant pitch screw in the form of an auger rotated within feeder body  66 . In the embodiment illustrated, dual screws  68  are utilized, and both of the screws may be constant pitch augers. The screws  68  may be formed of stainless steel or other suitable materials. As further illustrated, each screw  68  comprises a central shaft  70  that extends through opposite end plates  72  of feeder body  66  for receipt in corresponding bearings  74 . 
         [0027]    The screws  68  are rotated by a gearbox  76  which may be mounted adjacent one of the end plates  72  and coupled with shafts  70 . The gearbox  76  may be powered by a suitable motor  78 , such as a hydraulic motor or an electric motor. In one example, gearbox  76  has a high gearbox drive ratio, and motor  78  comprises a small volumetric displacement hydraulic motor that provides great control at low speeds. 
         [0028]    Each of the feeder components is designed to function well with the desired additive. For example, the dual screws  68  and open inlet  64  may be arranged in a compact, low-profile design and used in cooperation with hopper  30  to provide a functionally effective construction for use with fiber products, such as fibrous fluid-loss reduction additives, such as those recited in U.S. Pat. Nos. 7,267,173 and 7,331,391, the entire disclosures of each of which are incorporated by reference in their entirety. Component materials also can be selected to facilitate the controlled and consistent movement of additive through both hopper  30  and feeder  28 . In various applications, feeder body  66  may be formed from stainless steel, for example, to reduce friction and to discharge any build up of static electricity. Additionally, gearbox  76 , motor  78 , hopper  30 , screws  68 , and feeder body  66  (including end plates  72 ) can be constructed as modular components held together by a variety of fasteners  80 . This high degree of modularity provides ease of assembly and disassembly when desired for initial construction, cleaning, repair, or other related operations. 
         [0029]    Referring to  FIG. 6 , a feeder outlet  82  is illustrated as positioned to allow the additive to move through feeder  28  and into cement mixing tank  24 . In the specific embodiment illustrated, the bottom side of screws  68  is shrouded by a shell  84  that may be a modular shell formed of a suitable material, such as stainless steel. The shell  84  wraps around the lower side of screws  68  to guide the additive material driven by screws  68  to an additive discharge opening  86 . Rotation of the screws  68  drives the additive material along the interior of shell  84  and discharges it through discharge opening  86  so the material can fall through feeder outlet  82  into cement mixing tank  24 . 
         [0030]    The feeder  28  may be constructed in a variety of sizes and configurations with various components to facilitate metering of additive material. For example, one or more flow control inserts  88  can be mounted in feeder body  66  to facilitate flow from hopper  30  into screws  68 , as illustrated in  FIG. 7 . In the specific example illustrated, flow control inserts  88  are removably mounted in feeder body  66  and may be formed of variable geometry to regulate movement of fiber additive or other types of additives. Depending on the additive material and the environment in which feeder  28  is used, flow control inserts  88  may be made from a variety of suitable materials, including stainless steel. 
         [0031]    Motor  78  and gearbox  76  also may have a variety of forms and configurations. In the embodiment illustrated in  FIG. 7 , for example, gearbox  76  is a right angle gearbox having internal gearing  90  arranged to rotate dual screws  68  in opposite directions. The internal gearing  90  can be changed to adjust the speed of rotation and to accommodate different numbers of screws  68  in other embodiments of feeder  28 . 
         [0032]    The system  20  is useful in a variety of cementing operations including, but not limited to, foamed cementing operations and a variety of well environments. The system  20  may be utilized for providing an additive to a variety of well servicing fluid including, but not limited to, drilling mud or drilling fluid, a foamed cement mixture, an acidizing mixture, a proppant additive, such as a coating additive, or other well servicing fluids for delivery into a wellbore, as will be appreciated by those skilled in the art. In one example of a methodology for using transportable cementing unit  20  and hopper system  26 , the transportable cementing unit  20  is driven to a well site for performance of a servicing operation. Once properly located at the well site, the hopper  30  is actuated to its expanded position to accommodate a desired amount of fibrous fluid-loss reduction additive. The additive is placed into hopper  30 , and feeder  28  is operated to meter a controlled amount of the fibrous fluid-loss reduction additive into cement mixing tank  24  of the transportable cementing unit  20 . The cement mixing tank is operated to mix in the additive and to form a desired cement slurry for a well cementing operation. Subsequently, the cement slurry is delivered downhole to a desired region of the wellbore to complete performance of the cementing operation. Once the cementing operation is completed, hopper system  26  can be converted to its contracted configuration and, if applicable, canopy  50  can be lowered to facilitate transport of the transportable cementing unit. 
         [0033]    The actual configuration of hopper system  26  and the overall transportable cementing unit  28  may vary depending on the additive or additives involved, the goals of the servicing operation, and the environment in which the operation is conducted. For example, the size and type of components used to construct hopper system  26  may vary depending on the specific application. Additionally, the materials used to form the various components may be different from one application to another, depending on the environment, the additive, and other factors affecting the cementing operation. The methodology of operating the hopper system and the cementing unit, as well as the methodology for mixing materials to form the cement slurry, can be adjusted and varied for different applications. 
         [0034]    Accordingly, although only a few embodiments have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.

Summary:
A technique facilitates well servicing operations by utilizing a hopper system to introduce a dry additive into a mixing tank. The hopper system comprises a feeder and a hopper that delivers the dry additive into the feeder. The feeder, in turn, enables introduction of the dry additive into the cement mixing tank in a controlled manner. When the hopper system is used on a transportable cementing unit, the hopper system may be mounted on a cement mixing tank and also may incorporate a hopper that is both expandable to accommodate a greater amount of dry additive and contractible to facilitate transport.