Abstract:
The present invention relates to a gel hydration tank and method for hydrating gels for use in oil well treatment operations according to which a mixture of water and gel is introduced into the interior of the tank and flows through the tank before being discharged from the tank, whereby specific devices are used to deflect and/or re-direct fluid flow so as to increase the distance traveled for a given fluid volume element, which consequently increases the plug flow efficiency of the tank.

Description:
BACKGROUND 
     This invention relates to a gel hydration tank and method for hydrating gels for use in oil and gas well treatment operations. 
     Well treatment fluids are often used in oil or gas wells for well completion procedures, to acidify the well formation, and/or increase the recovery of hydrocarbons from the well by creating fractures in the formations, and the like. Many well treatment fluids of this type are composed of water and polymer gel agents and are usually formed by transporting an appropriate polymer gel agent to the well site and mixing it with excess water before the mixture is transferred to a hydration tank. The mixture is introduced into the hydration tank and the finished fluid is withdrawn from the tank on a continuum, yet the mixture must be maintained in the tank an optimum time to allow the polymer gel agent to become hydrated to form a high viscosity well treatment fluid. Thus, the design of the hydration tank is important to ensure the above and thus form an optimum well treatment fluid. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of a typical oil well treatment operation incorporating a hydration tank. 
     FIG. 2A is a top plan, broken-away, view of a hydration tank according to one embodiment of the present invention. 
     FIG. 2B is a side elevational view of the hydration tank of FIG.  2 A. 
     FIGS. 3 and 4 are cross-sectional views taken along the lines  3 — 3  and  4 — 4 , respectively, of FIG.  2 B. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a typical well treatment operation  10 , where a high viscosity well treatment fluid is processed for introduction into subterranean well formations. In the well treatment operation  10 , an appropriate polymer gel agent is transported to the well site, and placed in a mixing container  12 . The polymer gel agent can include dry polymer additives, stabilized polymer slurries, aqueous liquid gel concentrates, and hydrocarbon-based liquid gel concentrates. 
     In the mixing container  12 , the polymer gel agent is mixed with excess water and then transferred to a hydration tank  14  to allow time for the polymer gel agent to become hydrated to form a high viscosity well treatment fluid. Although the transformation from a polymer gel agent and water mixture to the resulting hydrated well treatment fluid is on a continuum, for the sake of simplicity the specification will refer to a fluid when it is not necessary to distinguish between the initial polymer gel agent and water mixture and the resulting hydrated well treatment fluid. 
     A pump  15  is used to transfer the hydrated fluid from the hydration tank  14  to a blending system  16 , whereby sand or another proppant and other liquid additives are accurately metered and mixed with the hydrated gel. Then, another pump  17  transfers the mixture to high pressure pumps  18  that pressurize and transfer the final mixture to the well bore  19 . In one embodiment, the well treatment operation  10  produces well treatment fluid substantially continuously. Thus, the hydration tank  14  must permit the flow of the well treatment fluid from the mixing container  12  to the pump  15  at a desired, substantially consistent, flow rate while allowing the fluid to remain in the hydration tank  14  for at least the hydrating period to ensure optimum viscosity for the resulting well treatment fluid. Thus, to establish an acceptable flow rate and residence time, the fluid should not “finger” ahead and enter the pump  15  before remaining in the hydration tank  14  for the hydration period. 
     As shown in FIGS. 2A and 2B, the hydration tank  14  according to one embodiment of the present invention includes a set of walls  22 ,  24 ,  26 , and  28  (wall  28  is removed for clarity in FIG.  2 B), extending perpendicular to a floor  30  and attached to the floor  30  in any conventional manner to define a fluid-tight interior portion  32 . A top  34  (partially shown in FIG. 2A) may be placed on top of the hydration tank  14  via structural members  36 , 38  to cover the interior portion  32 . 
     An inlet pipe  40  extends through the wall  26  and adjacent to the wall  28  for receiving the polymer gel agent and water from the mixing container  12  (FIG. 1 ) and introducing the fluid into the interior portion  32 . Fluid entry is controlled by mixing container  12 . An inlet valve  42  is provided for isolating the hydration tank  14  from the mixing container  12 . An outlet pipe  46  extends from the interior portion  32  and adjacent to the wall  24  to the exterior of the hydration tank  14  for allowing the discharge of the hydrated well treatment fluid from the hydration tank  14 . Fluid exit is controlled by the pump  15 . An exit valve  47  is provided for isolating the hydration tank  14  from the blending system  16 . Thus, there is a general fluid flow through the interior portion  32  from the inlet pipe  40  to the outlet pipe  46 . 
     The hydration tank  14  is mobile and includes a base  50  with an attached connector  52  at one end for coupling to a conventional motive source, such as a truck (not depicted). A wheel assembly  54  is attached to the other end of the base  50 . 
     A plurality of weirs  60 - 69  are disposed in the interior portion  32  of the hydration tank  14  in a spaced, parallel relation to establish a flow path of the fluid from the inlet pipe  40  to the outlet pipe  46 . As shown in FIG. 3, the weir  60  is a flat, plate-like structure having a top  70 , a flat side  72 , a bottom  74 , and a slanted side  76 . The top  70  is attached to the structural member  36 , which spans between wall  24  and wall  28  and is positioned adjacent to the top  34  of the hydration tank  14 . The flat side  72  is attached to the wall  28 , and the bottom  74  is attached to the floor  30 . The slanted side  76  is spaced from the wall  24  and creates a specific directional path for fluid to flow. 
     The weir  61  is shown in FIG.  4  and is also a flat, plate-like structure having a top  80 , a flat side  82 , a bottom  84 , and a slanted side  86 . The top  80  is attached to the structural member  38 , which spans between wall  24  and wall  28  and is positioned adjacent to the top  34  of the hydration tank  14 . The flat side  82  is attached to the wall  24 , and the bottom  84  is attached to the floor  30 . The slanted side  86  is spaced away from the wall  28 , and creates a specific directional path for fluid to flow. Thus, the weir  61  is substantially similar to the weir  60 , but is installed on the laterally opposing wall and is in an inverted orientation relative to the weir  60 . 
     The weirs  62 ,  64 ,  66 , and  68  are also connected to the wall  28  and are substantially identical to the weir  60 ; and the weirs  63 ,  65 ,  67 , and  69  are also connected to the wall  24  and are substantially identical to the weir  61 . Therefore, the weirs  62 ,  63 ,  64 ,  65 ,  66 ,  67 ,  68 , and  69  will not be described in detail. 
     In operation, the fluid flows from the mixing container  12  (FIG. 1) and into the hydration tank  14  through the inlet pipe  40  (FIGS.  2 A and  2 B), before passing into and through the interior portion  32  of the hydration tank  14  and discharging from the outlet pipe  46 . During this flow through the interior portion  32 , the fluid is deflected by the weirs  60 - 69  in a manner to be described, and passes around the weirs  60 - 69 , with each of the weirs  60 - 69  establishing its own fluid volume movement. 
     The general vector for the fluid volume movement for each of the weirs  60 - 69  is dependent on the above-described spaces between the slanted sides of the weirs and the relevant opposing wall. More particularly, the fluid entering the interior portion  32  of the hydration tank  14  from the inlet pipe  40  initially encounters the weir  60 . The fluid volume movement around the weir  60  is shown in FIG. 3 by the reference arrow B 1 . The fluid is blocked from passing between the weir  60  and each of the wall  28 , the floor  30  and the top  34 . Thus, the fluid must flow to the space between the wall  24  and the slanted side  76 , generally to the right in FIG.  3 . Also, since more fluid volume will pass through the relatively larger space between the wall  24  and portions of the slanted side  76  closer to the bottom  74 , the flow is generally downwardly, as also shown by B 1 . 
     The fluid next encounters the weir  61  described with reference to FIG.  4 . The fluid is blocked from passing between the weir  61  and each of the wall  24 , the floor  30  and the top  34 . Thus, fluid must flow to the space between the wall  28  and the slanted side  86 , generally to the left in FIG. 4 as shown by B 2 . Also, since more fluid volume will pass through the relatively larger space between the wall  28  and portions of the slanted side  86  closer to the top  80 , the flow is generally upwardly, as also shown by B 2 . 
     It can be readily appreciated that each weir  60 - 69  establishes its own fluid volume movement, the even-reference numbered weirs  60 ,  62 ,  64 ,  66 , and  68  producing fluid volume movements substantially similar to B 1 , and the odd-reference numbered weirs  61 ,  63 ,  65 ,  67 , and  69  producing fluid volume movements substantially similar to B 2 . 
     Thus, the fluid flows in a direction in a horizontal plane of the hydration tank  14  as depicted in FIG.  2 A and denoted by the reference arrow H 1 ; whereas the fluid then flows in another direction in a horizontal plane of the hydration tank  14  as denoted by the reference arrow H 2 . The alternate juxtaposition of odd-reference numbered weirs  61 ,  63 ,  65 ,  67 , and  69  and even-reference numbered weirs  60 ,  62 ,  64 ,  66 , and  68 , along the walls  24  and  28 , respectively, and the staggered spaced openings, create an alternating pattern of flows H 1  and H 2 . 
     Also, the fluid flows in a direction in a vertical plane of the hydration tank  14  as depicted in FIG.  2 B and denoted by the reference arrow V 1 ; and in another direction in a vertical plane of the hydration tank  14  as denoted by the reference arrow V 2 . As noted above, the alternate juxtaposition of the slanted sides of the odd-reference numbered weirs  61 ,  63 ,  65 ,  67 , and  69  and even-reference numbered weirs  60 ,  62 ,  64 ,  66 , and  68 , create an alternating pattern of flows V 1 , and V 2 . Thus, the movement of fluid (H 1  and H 2 , V 1  and V 2 ) through the hydration tank  14  in the above manner lengthens the distance traveled by the fluid, thus increasing the residence time to ensure hydration of the fluid in the hydration tank  14 , and allows the use of faster flow rates. 
     Variations and Equivalents 
     It is understood that the number of weirs disposed in the hydration tank  14  is disclosed only for illustrative purposes and that the invention contemplates the use of any number of weirs to create a desired flow rate, the number and size of the weirs being readily calculable based on the hydration tank  14  dimensions and hydrating period. Furthermore, the plug flow efficiency will increase with additional number of weirs, up to a limit. 
     Furthermore, it is understood that while the weirs show a slanted side for deflecting the fluid, an embodiment is also contemplated wherein the weirs have straight sides and the walls of the hydration tank  14  are slanted to deflect the fluid. Moreover, although a mobile embodiment of the hydration tank  14  is depicted in the drawings, it is understood that the hydration tank  14  may have various immobile embodiments. 
     It is also understood that all spatial references, such as “top”, “bottom”, “left”, “right”, “front”, “back”, “downwardly”, “upwardly”, “horizontal”, and “vertical” are for illustrative purposes only and can be varied within the scope of the invention. 
     Furthermore, it is understood that the essential flow patterns shown in the figures and described herein are for example only and the flow patterns may have directions other than horizontal and vertical. 
     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 other 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. For example, small holes may be cut in the bottom of each weir (at the intersection of floor  30  and bottom  74  in FIG.  3  and floor  30  and bottom  84  in FIG. 4) to facilitate complete drainage during cleanup.