Abstract:
A portable fluid storage tank has through pipes with opposed ends that extend through the tank at two separate places so that the opposed ends are exposed on an exterior of the portable fluid storage tank and the each through pipe provides a separate fluid path through the portable fluid storage tank without fluid communication between the through pipes or an interior of the portable fluid storage tank. Several rows of the portable fluid storage tanks can be connected to a single frac manifold to reduce well site space usage.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to portable fluid storage tanks and, in particular, to a large capacity portable fluid storage tank used to store well fracturing fluids. 
       BACKGROUND OF THE INVENTION 
       [0002]    Portable fluid storage tanks used to store well fracturing fluids are well known in the art. Such tanks are available in two general types: trailer tanks and skidded tanks. Trailer tanks are horizontal tanks shaped much like a semi-truck trailer and have at least one rear axle with wheels. Trailer tanks generally have a capacity of about 350-500 barrels. They are towed by a trailer tractor to a well site and parked in side-by-side and back-to-back double rows. A frac manifold must be installed between each pair of double rows to pump fluid from the tanks. Skidded tanks are cylindrical tanks with skids welded to a side surface. The skidded tanks generally have a capacity of about 200-500 barrels. The skidded tanks are transported to a well site on specially designed trucks or trailers, where they are offloaded and normally tipped to an upright position using cables or chains pulled by winches or a suitable vehicle. 
         [0003]    Each type of tank has its advantages and disadvantages. Trailer tanks have a low profile but occupy a large area per barrel of fluid capacity. Skidded tanks, once tipped upright, occupy less area per barrel of fluid capacity, but they require much more handling, space for the tipping operation, and they cannot be as closely packed because of the tipping operation. 
         [0004]    Fracturing a gas well in a shale formation, for example, often requires a very large volume of fracturing fluid. Since it is only economical to fracture the well in a single uninterrupted procedure due to equipment rental and labor costs, all of the required fracturing fluid must be stored at the well site before the fracturing operation begins. If a large frac is to be performed, an appropriately sized area around the well must be prepared for the frac tanks and other equipment required to perform the fracturing operation. The required area must be acquired or leased, graded and, if necessary, covered with an appropriate surface aggregate. All of this is time-consuming, expensive and environmentally undesirable. It is therefore desirable to keep the well site as small as possible. In order to facilitate this, space-efficient fluid storage is advantageous. 
         [0005]    There therefore exists a need for a portable fluid storage tank that provides space-efficient fluid storage. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of the invention to provide a portable fluid storage tank that has a small footprint to provide space-efficient fluid storage. 
         [0007]    The invention therefore provides a portable fluid storage tank, comprising: a base that supports the portable fluid storage tank in an upright position; a bottom wall connected to the base; at least one sidewall connected to the bottom wall; a top wall connected to the at least one sidewall; at least one through pipe having opposed ends, the at least one through pipe extending through the at least one sidewall at two separate places so that the respective opposed ends of the at least one through pipe are exposed on an exterior of the portable fluid storage tank and the at least one through pipe provides a fluid path through the portable fluid storage tank without fluid communication between the at least one through pipe and an interior of the portable fluid storage tank; and, at least one drain valve through which fluid may be removed from the portable fluid storage tank. 
         [0008]    The invention further provides a portable fluid storage tank, comprising: a base that supports the portable fluid storage tank in an upright position; a bottom wall connected to the base; four sidewalls connected to the bottom wall; a top wall connected to the four sidewalls; a plurality of through pipes respectively having opposed ends, the plurality of through pipes respectively extending through two opposed ones of the four sidewalls, so that the respective opposed ends of the respective plurality of through pipes are exposed on an exterior of the portable fluid storage tank and the plurality of through pipes respectively provide a fluid path through the portable fluid storage tank without fluid communication between any one of the plurality of through pipes and an interior of the portable fluid storage tank; and, at least one drain valve through which fluid may be removed from the portable fluid storage tank. 
         [0009]    The invention yet further provides a method of storing fracturing fluid at a well site, comprising: arranging at the well site a plurality of portable fluid storage tanks in rows and columns, the portable fluid storage tanks respectively comprising a plurality of through pipes that provide a fluid path through the respective portable fluid storage tanks without fluid communication between any one of the through pipes and an interior of the respective portable fluid storage tanks and at least one drain valve through which fluid may be removed from the portable fluid storage tank, the rows and columns being arranged so that a first row faces a frac manifold, and the number of rows in each column does not exceed the number of through pipes in each of the plurality of portable fluid storage tanks, plus one; connecting the drain valves of the portable fluid storage tanks in the first row directly to the frac manifold; and interconnecting the drain valves of the respective portable fluid storage tanks in the remaining rows to a through pipe in a next row closer to the frac manifold to commence a segregated fluid path to the frac manifold, daisy chaining each through pipe in a segregated fluid path to a through pipe in the first row, and connecting to the frac manifold each through pipe in the first row that forms part of one of the segregated fluid paths to create a complete segregated fluid path from each drain valve to the frac manifold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, in which: 
           [0011]      FIG. 1  is a schematic side elevational view of an embodiment of a portable fluid storage tank in accordance with the invention, showing a truck with a tilting bed used to transport the portable fluid storage tank to a well site; 
           [0012]      FIG. 2  is a schematic bottom plan view of the portable fluid storage tank shown in  FIG. 1 ; 
           [0013]      FIG. 3  is a schematic top plan view of the portable fluid storage tank shown in  FIG. 1 ; 
           [0014]      FIG. 4  is a schematic cross-sectional view of a top end of the portable fluid storage tank shown in  FIG. 1 , taken along lines  4 - 4  of  FIG. 3 ; 
           [0015]      FIG. 5  is a partial cross-sectional view of a handrail shown in  FIG. 4 ; 
           [0016]      FIG. 6  is a schematic cross-sectional view of a bottom end of the portable fluid storage tank shown in  FIG. 1 , taken along lines  6 - 6  of  FIG. 3 ; 
           [0017]      FIG. 7  is a schematic side elevational view of the top end of the portable fluid storage tank shown in  FIG. 1 , illustrating latch windows engaged by hydraulic latches of the tilting truck bed shown in  FIG. 1  to secure the portable fluid storage tank to the tilting truck bed; 
           [0018]      FIG. 8  is a schematic diagram of a portion of a cradle of the tilting truck bed used to transport the portable fluid storage tank shown in  FIG. 1 ; 
           [0019]      FIG. 9  is a schematic front elevational view of a hydraulic latch of the tilting truck bed shown in  FIG. 1 ; 
           [0020]      FIG. 10  is a schematic side elevational view of the hydraulic latch shown in  FIG. 9 ; 
           [0021]      FIG. 11  is a schematic side elevational view of one column of four portable fluid storage tanks in accordance with the invention connected to a frac fluid manifold at a well site and; 
           [0022]      FIG. 12  is a rear elevational view of a row of four columns of the portable fluid storage tanks shown in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    The invention provides a portable fluid storage tank especially adapted to store fracturing fluid used for well stimulation procedures. The portable fluid storage tank has a small footprint, a large fluid capacity, and through pipes that permit efficient use of well site space by enabling the connection of a plurality of rows of portable fluid storage tanks to a single frac manifold. Thus well site space and frac manifold rental expenses are reduced. The portable fluid storage tank also has a top end walkway with handrails to permit well site personnel to walk more safely across a top of rows of the portable fluid storage tanks, when required. 
         [0024]      FIG. 1  is a schematic side elevational view of one embodiment of a portable fluid storage tank  20  in accordance with the invention. In this embodiment, the portable fluid storage tank  20  is substantially square with rounded corners  22 . In one embodiment, the portable fluid storage tank  20  is about 11′×11′ (3.35×3.35 m) and the rounded corners  22  each have a radius of about 2′ (0.61 m). A tank of this dimension with a height of about 30′ (9.15 m) has a capacity of about 750 barrels (119,242 L). In one embodiment the portable fluid storage tank  20  is constructed of ¼″ (6.3 mm) mild steel and has a weight of about 15,000 lb (6,818 kg). For corrosive fluid applications, the portable fluid storage tank  20  may be constructed of galvanized or stainless steel. 
         [0025]    The portable fluid storage tank  20  is supported on a cross-shaped base  24  constructed from a plurality of 6′×6′ (15×15 cm) square steel tubes  26  welded to a bottom wall  21  of the portable fluid storage tank  20 , as will be explained below in more detail with reference to  FIG. 2 . The square steel tubes  27  have a wall thickness of about ⅜″ (9.53 mm). A top wall  23  of the portable fluid storage tank  20  is constructed with a covered manhole  28 . A collapsible handrail  30  and a walkway  32  (see  FIG. 3 ) are also connected to the top wall  23 , as will be explained in more detail below with reference to  FIG. 3 . 
         [0026]    In this embodiment, the portable fluid storage tank  20  includes at least two drain valves  34 , typically butterfly valves located adjacent a bottom wall  21  of the portable fluid storage tank  20 . The drain valves have an internal diameter of about 4″ (10 cm). The portable fluid storage tank also includes a plurality of through pipes  36 , which respectively extend completely through and are welded to opposite sidewalls of the portable fluid storage tank  20 . The through pipes  36  provide fluid passages through the portable fluid storage tank  20  to permit fluid to be pumped from other portable fluid storage tanks  20 , as will be explained below in more detail with reference to  FIGS. 6 and 11 . Each of the through pipes  36  also has a diameter of about 4″ (10 cm). 
         [0027]    The portable fluid storage tank  20  is transported by truck  40  having a tilting bed  42 . The tilting bed  42  is raised and lowered by a scissor frame  44  similar to one described, for example, in U.S. Pat. No. 4,148,528, which issued on Apr. 10, 1979 to Channell, the specification of which is incorporated herein by reference. The tilting bed  42  pivots around pivot pins  44  journaled through bearings installed in a rear end of the truck frame  46 . A tank cradle having tank cradle arms  48  supports the portable fluid storage tank  20  on the tilting bed  42 . The tank cradle arms  48  are curved to match the rounded corners of the portable fluid storage tank  20  as will be described below in more detail with reference to  FIG. 8 . Hydraulic latches  50 , described below in more detail with reference to  FIGS. 9 and 10 , in cooperation with a tilting bed end plate  52  secure the portable fluid storage tank  20  to the tilting bed  42 . As will be explained below in more detail with reference to  FIG. 7 , the hydraulic latches  50  engage latch windows in a sidewall  60  of the portable fluid storage tank  20  and lift the portable fluid storage tank  20  upwardly until the top end wall  23  of the portable fluid storage tank  20  abuts the tilting bed end plate  52  to lock the portable fluid storage tank  20  to the tilting bed  42 . 
         [0028]      FIG. 2  is a schematic bottom plan view of the portable fluid storage tank  20  shown in  FIG. 1 . As explained above, the portable fluid storage tank  20  is supported on a base  24  constructed from a plurality of 6′×6′ (15.24×15.24 cm) square steel tube side members  26   a - 26   d  having a wall thickness of about ⅜″ (9.5 mm). The steel tube side member  26   a  is welded to the bottom wall  21  of the portable fluid storage tank  20  along a bottom edge of the front wall  54 . The steel tube side member  26   b  is welded to the bottom wall  21  of the portable fluid storage tank  20  along a bottom edge of a left sidewall  56 . The steel tube side member  26   c  is welded to the bottom wall  21  along a bottom edge of a rear sidewall  58 , and the steel tube side member  26   d  is welded to the bottom wall  21  along a bottom edge of a right sidewall  60 . A steel tube cross-member  25   a  of the same dimension is welded between the steel tube side members  26   b  and  26   d.  A steel tube cross-member  25   b  is welded between the cross-member  25   a  and the steel tube side member  26   a,  and a steel tube cross-member  25   c  is welded between the cross-member  25   a  and the steel tube side member  26   c.  The steel tube base  24  not only securely supports the portable fluid storage tank  20 , but also provides open channels into which steam, or the like, can be directed to release the portable fluid storage tank  20  if it freezes to the ground, which can occur under certain winter conditions. 
         [0029]    As also explained above, two drain valves  34   a,    34   b  are secured to a bottom of the front wall  54 . Fluid is pumped from the portable fluid storage tank  20  through one or both of the drain valves  34   a,    34   b.  In this embodiment, four through pipes  36   a - 36   d  are provided. Each through pipe  36   a - 36   d  extends completely through the portable fluid storage tank  20  and is welded to the respective front wall  54  and a rear wall  58 . As will be explained below in more detail with reference to  FIG. 6 , the through pipes  36   a - 36   d  provide a fluid flow path through the portable fluid storage tank  20 , but there is no fluid communication between the through pipes  36   a - 36   d  and the inside of the portable fluid storage tank  20 . 
         [0030]      FIG. 3  is a schematic top plan view of the portable fluid storage tank  20  shown in  FIG. 1 . As explained above, the top of the portable fluid storage tank  20  is provided with handrails  30   a,    30   b.  The handrails  30   a,    30   b  flank opposite sides of a walkway  32  which extends between the sidewalls  56 ,  60 . The handrails  30   a,    30   b  are supported by posts  68  that slide inside tubes welded inside a top of the portable fluid storage tank  20 , as will be explained below in more detail with reference to  FIG. 4 . The walkway  32  is preferably constructed of steel plate with a textured surface, or some other non-slip surface treatment. In this embodiment, the manhole  28  is about 2′ (61 cm) in diameter and includes a manhole cover  62  that is hinged to the top wall  23  of the portable fluid storage tank  20  by a hinge  66  to permit the manhole cover  62  to be easily displaced so that fluid levels can be checked, etc. In this embodiment, the manhole  28  is round and the cover  62  is secured by a locking mechanism (not shown) operated by a hand wheel  64 , well known in the art. It should be understood that any shape of manhole and any type of manhole cover can be used, as can any type of locking mechanism for the cover. 
         [0031]      FIG. 4  is a schematic cross-sectional view of a top end of the portable fluid storage tank  20  shown in  FIG. 1 , taken along lines  4 - 4  of  FIG. 3 . As explained above, the handrails  30   a  and  30   b  are supported by posts  68 , which are tubular or solid members that are received in hollow tubes  70 . The posts  68  and the tubes  70  may have any cross-sectional shape that permits the handrails  30   a  and  30   b  to be easily raised from a lowered position for transport to a raised position for field use, and vice versa. The tubes  70  extend through holes in the top wall  23  and are welded to the top wall  23 . Transverse bores near a top end of the tubes  70  and complementary bores through a bottom of the posts  68  receive pins  72  to lock the posts  68  in the raised position. A stabilizer  78 , which may be of plate or tubular stock, extends between the sidewalls  56  and  60  and is welded or otherwise secured to the respective sidewalls. The stabilizer  78  is welded to a bottom of each tube  70  to stabilize the respective tubes  70  and prevent fluid from migrating from the portable fluid tank into the bottom end of the tubes  70 . A rectangular beam  80  is welded to the sidewall  60  and to a bottom of the stabilizers  78 . The rectangular beam  80  reinforces the sidewall  60  at the latch windows, as will be explained below with reference to  FIG. 7 . 
         [0032]      FIG. 5  is a partial cross-sectional view of the handrail  30   b  shown in  FIG. 4 . As explained above, the posts  68  are supported in the raised position by pins  72  that are locked in place by lock pins  74 , which may be self-locking pins well known in the art, or any other suitable type of fastener. A transverse bore  76  through a top of the posts  68  near the handrail  30   b  is used to lock the handrails in the lowered, transport position shown in  FIG. 1 . The pins  72  and the lock pins  74  are used to lock the posts  68  in the lowered position. 
         [0033]      FIG. 6  is a schematic cross-sectional view of a bottom end of the portable fluid storage tank  20  shown in  FIG. 1 , taken along lines  6 - 6  of  FIG. 3 . In this cross-section, only the through pipe  36   a  can be seen. Each of the through pipes  36   a - 36   d  extends completely through the portable fluid storage tank  20 , and opposed ends of each through pipe  36   a - 36   d  extend about 6″ (15 cm) beyond the respective front sidewall  54  and the rear sidewall  58 . As can be seen, there is no fluid communication between the through pipes  36   a - 36   d  and the inside of the portable fluid storage tank  20 . The through pipes  36   a - 36   d  in this embodiment are conveniently located at about 3′6″ (1.09 m) above a top of the base  24 . However, the through pipes  36   a - 36   d  may be located any convenient distance above the base  24 . The through pipes  36   a - 36   d  are inserted through holes cut in the front sidewall  54  and the rear sidewall  58 . A circumferential weld  82  secures the through pipe  36   a  to the rear sidewall  58  of the portable fluid storage tank  20 . A circumferential weld  84  secures of the through pipe  36   a  to the front sidewall  54 . The other through pipes  36   b - 36   d  are welded to the front sidewall  54  and a rear sidewall  58  in the same way. 
         [0034]    As can be seen, the drain valves  34   a,    34   b  are located as close to the bottom wall  21  as practical. A gusset  86  may be welded, on one or both sides of the valve opening (not shown), to the bottom wall  21  and the bottom of the front sidewall  54  to reinforce the front sidewall  54  against strain induced by the connection of the hoses, etc. to the drain valves  34   a,    34   b.    
         [0035]      FIG. 7  is a schematic side elevational view of a top end of the portable fluid storage tank  20  shown in  FIG. 1 , illustrating latch windows  88   a,    88   b  that are engaged by the hydraulic latches  50  of the tilting truck bed  42  ( FIG. 1 ) to secure the portable fluid storage tank  40  to the tilting truck bed  42 . In this embodiment, a 6″×8″ rectangular tubular beam  80  having a wall thickness of about ⅜″ (9.5 mm). The tubular beam  80  has opposite ends  87   a,    87   b  that are respectively contoured to closely mate with the rounded corners  22  of the sidewall  60 . The top, bottom and end edges of the tubular beam are welded to the sidewall  60  and the rounded corners  22  so that there is no fluid communication between the inside of the portable fluid storage tank  20  and the tubular beam  80 , and so that the tubular beam  80  is securely bonded to the sidewall  60  and the rounded corners  22 . The latch windows  88   a,    88   b  are cut through the sidewall  60  and the front side of the tubular beam  80 . Angle iron or channel iron (not shown) may be welded around the perimeter of each of the windows  88   a,    88   b  to further reinforce them. In this embodiment, the latch windows  88   a,    88   b  are respectively about 12 inches (30 cm) long and 6 inches (15 cm) high. 
         [0036]      FIG. 8  is a schematic diagram of one cradle arm  48  of the tilting truck bed  42  used to transport the portable fluid storage tank shown in  FIG. 1 . In order to facilitate pickup or drop-off of the portable fluid storage tank  20  from/to a surface that may not be perfectly level, the cradle arms  48  on at least one side of the tilting truck bed  42  are preferably movable from a retracted transport position to an extended pickup and drop-off position. The cradle arm  48  shown in  FIG. 8  is in the extended pickup/drop-off position. The cradle arm  48  reciprocates through a housing  92 , which may be constructed of tubular material. The housing  92  is welded or otherwise secured to a frame member  90  of the tilting truck bed  42  by gussets  94 , or any other suitable fastener. At least the inner end of the cradle arm  48  is hollow and slides over bar stock  96  secured to a cradle bed  98  also supported (not shown) by the tilting truck bed  42 . A hydraulic cylinder  100  is used to reciprocate the cradle arm  48  from the retracted transport position to the extended pickup position. A piston rod  102  of the hydraulic cylinder  100  is connected by a fastener  104  and a bushing  106  to the cradle arm  48 . The other cradle arms  48  on the same side of the tilting truck bed  42  are constructed in the same way. Alternatively, all of the cradle arms on the same side of the tilting truck bed  42  may be connected to a single hydraulic cylinder through a linkage (not shown) to move them from the travel position to the pickup/drop-off position. 
         [0037]      FIG. 9  is a schematic front elevational view of one of two hydraulic latches  50  of the tilting truck bed  42  shown in  FIG. 1 . Each of the hydraulic latches  50  has an outwardly extending tongue  120 , in this embodiment about 6 inches (15 cm) long and about 6 inches (15 cm) wide that is welded to a tubular or bar stock  122  having a free top end  124  and a journaled bottom end  126 . The free top end  124  is received in a tubular guide member  128  and reciprocates therein. The journaled bottom end  126  is secured by a fastener  130  to a ram  132  of a hydraulic cylinder  134 . The hydraulic cylinder  134  and the tubular guide member  128  are respectively secured to the tilting truck bed  42 . 
         [0038]      FIG. 10  is a schematic side elevational view of the hydraulic latch  50  shown in  FIG. 9 . The tilting truck bed  42  is not shown in this figure. As shown in  FIG. 1 , the two hydraulic latches are positioned on the tilting truck bed  42  so that the outwardly extending tongues  120  enter the respective latch windows  88   a  and  88   b  when the truck is backed up in proper alignment against the portable fluid storage tank  20 . When the rams  132  of the hydraulic cylinders  134  are extended, the downward and inward curvatures  138  of the outwardly extending tongues  120  of the hydraulic latches  50  urge the portable fluid storage tank  20  against the tilting truck bed  42 . A cradle arm control is then operated to move the cradle arms to the travel position, as discussed above with reference to  FIG. 8 . Further extension of the rams  132  raises the portable fluid storage tank  20  until the top end abuts the tilting truck bed end plate  52  ( FIG. 1 ), which locks the portable fluid storage tank  20  to the tilting truck bed  42 . After the portable fluid storage tank  20  is locked to the tilting truck bed  42 , the tilting truck bed  42  can be lowered into the transport position and the portable fluid storage tank  20  hauled to another location without additional strapping. To offload the portable fluid storage tank  20 , the loading operation is reversed, which permits the truck driver to offload the tank without assistance or auxiliary equipment and without any requirement to handle the tank or other equipment. 
         [0039]      FIG. 11  is a schematic side elevational view of one column of four portable fluid storage tanks  20   a - 20   d  connected to a frac fluid manifold  176  at a well site. The embodiment of the portable fluid storage tank  20  shown in  FIGS. 1-8  permits up to 5 rows of frac tanks  20  to be connected to a single frac manifold  176 . The number of columns of tanks connected to the frac manifold is limited only by the length of the frac manifold  176  and/or the size of the well site. It should also be understood that the number of rows of portable fluid storage tanks  20  in a column is limited only by the number of through pipes  36  with which each portable fluid storage tank  20  is provisioned. Four through pipes  36  is exemplary only and any number of through pipes  36  may be provided in the portable fluid storage tank  20  in accordance with the invention. 
         [0040]    In the example shown in  FIG. 11 , the drain valve  34   a  of the portable fluid storage tank  20   a  is connected by a flexible hose  150  and a suitable connector  152  to the through pipe  36   a  of the portable storage tank  20   b.  The drain valve  34   a  of the portable fluid storage tank  20   b  is connected via hose  154  and connector  156  to the through pipe  36   a  of the portable fluid storage tank  20   c.  The through pipe  36   a  of the portable fluid storage tank  20   b  is connected to the through pipe  36   b  (not visible) of the portable fluid storage tank  20   c  by the connector  158  and the flexible hose  160 . The drain valve  34   a  of the portable fluid storage tank  20   c  is connected via hose  162  and connector  164  to the through pipe  34   a  of the portable fluid storage tank  20   d.  The through pipe  36   a  of the portable fluid storage tank  20   c  is connected via hose connector  166  and hose  168  to the through pipe  36   b  (not visible) of portable fluid storage tank  20   d.  The through pipe  36   c  (not visible) of the portable fluid storage tank  20   c  is connected via connectors (not visible) and hose  170  to the through pipe  36   c  (not visible) of the portable fluid storage tank  20   d.    
         [0041]    The drain valve  34   a  of the portable fluid storage tank  20   d  is connected via hose  172  and connector  174  to the frac manifold  176 , which is supported by frac manifold base  178 . The through pipe  36   a  of the portable fluid storage tank  20   d  is connected via connectors  180  and  184  and hose  182  to the frac manifold  176 . The through pipe  36   b  (not visible) is connected to the frac manifold  176  by hose  186  and appropriate connectors (not visible), and the through pipe  36   c  (not visible) of the portable fluid storage tank  20   d  is connected to the frac manifold  176  by hose  188  and appropriate connectors (not visible). 
         [0042]    Thus, each of the portable fluid storage tanks  20   a - 20   d  is connected by a segregated fluid path to the frac manifold  176 . Fluid flow from any one of the portable fluid storage tanks  20   a - 20   d  can be controlled using the respective drain valves and/or by frac manifold control functions available through a frac manifold control panel (not shown). Hose use and hose clutter is kept to a minimum and storage tank clustering density is substantially increased, so the well site space required for fracturing fluid storage is significantly reduced. It should be noted that the hose connections shown in  FIG. 11  may be rigid pipe connections, the fluid paths between the respective portable fluid storage tanks  20   a - 20   d  can be daisy-chained to the through pipes  36  in any order without affecting the integrity of the segregated fluid path, and the distance between the rows of portable fluid storage tanks can be reduced to any comfortable working space, i.e. as little as 2′-3′ (0.6-1 m). 
         [0043]      FIG. 12  is a rear elevational view of a row of four adjacent columns of the portable fluid storage tanks  20  shown in  FIG. 11 . Because of space constraints, only the row farthest from the frac manifold  176 , and only four columns of that row are shown. The portable fluid storage tanks  20   a  (see  FIG. 11 ),  20   d,    20   e  and  20   f  are positioned as closely together as is practical. Site conditions will have an effect, but 2″-10″ (15-37.5 cm) between the portable fluid storage tanks  20  in adjacent columns is normally achievable. After all of the portable fluid storage tanks  20  for a given row have been delivered and positioned, a portable stairway  200 , or the like, is set up on one end of the row. The portable stairway  200  is available in many different styles, and well known in the art. It has wheels  202  that permit it to be towed to a well site using a tow bar (not shown). A height adjustment mechanism schematically shown at  204  is used to adjust the stairway to the required height (30′). The stairs  206  and the handrails  208  are self-leveling. 
         [0044]    The portable stairway  200  provides access to a top of the row of portable fluid storage tanks  20 . Once access is gained, the handrails  30  are raised and locked in place, as explained above with reference to  FIGS. 4 and 5 . The handrails  30   a,    30   b  help ensure that a row of the portable fluid storage tanks  20  can be more safely traversed by the frac crew, if required. 
         [0045]    The portable fluid storage tanks  20  described above are square with rounded corners. However, it should be understood that they may be rectangular or cylindrical without departing from the spirit or scope of the invention. Furthermore, although the portable fluid storage tanks  20  described above are constructed from steel plate, fiberglass or plastic could be used for the same purpose. 
         [0046]    The embodiments of the invention described above are therefore intended to be exemplary only. The scope of the invention is intended to be limited solely by the scope of the appended claims.