Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application which claims priority from U.S. provisional application No. 61/940,080, filed Feb. 14, 2014, which is incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD/FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates in general to the distribution of liquids, and specifically to measurement of liquid dispensed from a container. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    In the oilfield industry, a variety of liquids may be utilized during many operations used in drilling, completing, and producing a well. For example, liquid used during hydraulic fracturing operations may include a variety of chemicals used to, for example, reduce friction, reduce surface effects, or otherwise affect the downhole formation during a fracturing process. Suppliers of these liquids may utilize Intermediate Bulk Containers to transport liquids to and between wellsites. Liquids are generally sold by volume used, and a given wellsite may only use a portion of the liquid supplied. Typically, volume used must be determined on site by direct measurement of fluid levels in the containers. 
       SUMMARY 
       [0004]    The present disclosure provides for a system for determining the amount of liquid dispensed from a fluid container. The system may include a fluid container, the fluid container at least partially filled with a liquid, the remainder of the interior of the fluid container filled with a gas. The fluid container may include at least one drain outlet positioned to allow the liquid to be dispensed from the fluid container. The fluid container may include a pressure transducer positioned to measure the differential pressure between the gas or the liquid and the surrounding environment. The system may include a control unit positioned to receive a differential pressure signal from the pressure transducer and positioned to calculate the volume of liquid dispensed. 
         [0005]    The present disclosure also provides for a method of measuring a volume of a liquid dispensed. The method may include filling, at least partially, a fluid container with a liquid, the remainder of the interior of the fluid container filled with a gas, the fluid container including at least one drain outlet positioned to allow the liquid to be dispensed from the fluid container, the fluid container including a pressure transducer positioned to measure the differential pressure between the gas or the liquid and the surrounding environment; reading the differential pressure from the pressure transducer to determine an initial pressure; dispensing at least a portion of the liquid from the fluid container; reading the differential pressure from the pressure transducer to determine a second pressure; calculating the volume of liquid dispensed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
           [0007]      FIG. 1  depicts a liquid delivery and accounting system consistent with embodiments of the present disclosure. 
           [0008]      FIGS. 2 ,  3  depict a cross section view of a fluid container consistent with embodiments of the present disclosure. 
           [0009]      FIG. 4  depicts a cross section view of a fluid container consistent with embodiments of the present disclosure. 
           [0010]      FIG. 5  depicts a cross section view of a fluid container consistent with embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
         [0012]      FIG. 1  depicts a liquid delivery system consistent with embodiments of the present disclosure.  FIG. 1  depicts fluid containers  101  positioned on flatbed  10  of truck  15 . Truck  15  may be used to, for example, deliver fluid containers  101  to a wellsite, return fluid containers  101  from the wellsite, or transfer fluid containers  101  between wellsites. Each of fluid containers  101  is at least partially filled with a liquid to be transferred. Fluid containers  101  include at least one drain  103  positioned to allow liquid to be drawn from the fluid container  101  to be used at the wellsite. In some embodiments, fluid containers  101  may be filled at a supply depot. At the supply depot, fluid containers  101  may be at least partially filled with the desired liquid. 
         [0013]    As depicted in  FIGS. 2 ,  3 , fluid container  101  may include differential pressure sensor  105  positioned to measure the differential pressure between the inside of fluid container  101  and the external environment. Differential pressure sensor  105  may be positioned in an existing aperture at the top of fluid container  101 , such as a bung hole. Differential pressure sensor  105  may output the differential pressure as an electrical signal via sensor wire  107 . As depicted in  FIG. 1 , sensor wire  107  may, when fluid container  101  is positioned on flatbed  10 , electrically connect to sensor bus  109 . Sensor bus  109  may serve to connect each fluid container  101  with control unit  111 . Sensor bus  109  may be positioned to run along the side of flatbed  10  to, for example, prevent a potential tripping hazard for one walking on flatbed  10 . 
         [0014]    Control unit  111  may be positioned to measure the differential pressure as output by each fluid container  101 , allowing control unit  111  to calculate the volume of liquid remaining in each fluid container  101 . In some embodiments, flatbed  10  may include a suspension system positioned to ensure any fluid containers  101  are level at the time of reading. In some embodiments, the suspension system may be an active suspension including, for example and without limitation, an air suspension system. 
         [0015]    In some embodiments, control unit  111  may include a display to display relevant data to a user including, for example and without limitation, starting liquid volume, current liquid volume, change in liquid volume, time of delivery, time of current and previous measurement, etc. In some embodiments, control unit  111  may include a printer to print, for example, a ticket, invoice, or receipt for the liquid used. In some embodiments, control unit  111  may output or print readings or measurements on demand and/or according to a schedule. In some embodiments, control unit  111  may include a data port capable of being connected to a wellsite network. In some embodiments, the data port may be, as understood in the art, an RS 232 compatible connection. 
         [0016]    In some embodiments, control unit  111  may be powered by a battery. In some embodiments, the battery may be recharged by a solar array. In some embodiments, the battery may be recharged by a wind turbine. In some embodiments, control unit  111  may also be capable of providing a closed pressure system. In some such embodiments, control unit  111  may be positioned to control a pump or to control a valve on a compressed gas container each positioned to provide pressurized gas to fluid container  101  to, for example, fill space in fluid container  101  left by dispensed fluid or to force fluid from fluid container  101 . 
         [0017]    In some embodiments, the combined gas law may be utilized to determine the amount of liquid that has been dispensed since the last time fluid container  101  was connected to control unit  111  by measuring, as depicted in  FIGS. 2 ,  3 , the change in pressure of gas  113  positioned within fluid container  101  as liquid  115  is dispensed. As understood in the art, the combined gas law may be approximated as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                     1 
                   
                   × 
                   
                     V 
                     1 
                   
                 
                 
                   T 
                   1 
                 
               
               = 
               k 
             
             , 
           
         
       
     
         [0000]    where P 1  is the pressure of gas  113 , V 1  is the volume of the gas, T 1  is the temperature of the gas, and k is a constant. The constant k remains the same value while conditions, such as pressure, volume, and temperature vary. Thus, extending the combined gas law to apply to a second set of parameters, the following equations may be derived: 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                     1 
                   
                   × 
                   
                     V 
                     1 
                   
                 
                 
                   T 
                   1 
                 
               
               = 
               
                 
                   
                     P 
                     2 
                   
                   × 
                   
                     V 
                     2 
                   
                 
                 
                   T 
                   
                     2 
                      
                     
                         
                     
                   
                 
               
             
             , 
             and 
           
         
       
       
         
           
             
               
                 V 
                 2 
               
               = 
               
                 
                   
                     P 
                     1 
                   
                   
                     P 
                     2 
                   
                 
                 · 
                 
                   
                     T 
                     2 
                   
                   
                     T 
                     1 
                   
                 
                 · 
                 
                   V 
                   1 
                 
               
             
             , 
           
         
       
     
         [0000]    where P 2 , V 2 , and T 2  are the pressure, volume, and temperature of gas  113  at the second point in time. 
         [0018]    Assuming that fluid container  101  is sealed at the time it is filled by the supply depot and no additional gas may enter thereinto, by measuring the change in pressure of gas  113  between the filled state and the at least partially emptied state (as well as the temperature change), the corresponding volume of liquid  115  dispensed may be calculated. The equation to do so may be derived as follows: 
         [0000]    
       
         
           
             
                 
             
              
             
               
                 V 
                 container 
               
               = 
               
                 
                   V 
                   gas 
                 
                 + 
                 
                   V 
                   fluid 
                 
               
             
           
         
       
       
         
           
             
                 
             
              
             
               
                 
                   Δ 
                    
                   
                       
                   
                    
                   
                     V 
                     gas 
                   
                 
                 + 
                 
                   Δ 
                    
                   
                       
                   
                    
                   
                     V 
                     fluid 
                   
                 
               
               = 
               0 
             
           
         
       
       
         
           
             
               Δ 
                
               
                   
               
                
               
                 V 
                 fluid 
               
             
             = 
             
               
                 
                   - 
                   Δ 
                 
                  
                 
                     
                 
                  
                 
                   V 
                   
                     gas 
                     . 
                   
                 
               
               = 
               
                 
                   ( 
                   
                     
                       V 
                       container 
                     
                     - 
                     
                       V 
                       
                         fluid 
                         . 
                         filled 
                       
                     
                   
                   ) 
                 
                  
                 
                   ( 
                   
                     
                       
                         
                           P 
                           filled 
                         
                         
                           P 
                           emptied 
                         
                       
                       · 
                       
                         
                           T 
                           emptied 
                         
                         
                           T 
                           filled 
                         
                       
                     
                     - 
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    where V container  is the volume of the container, ΔV gas  and ΔV fluid  are the change in volume of the gas and liquid respectively, V liquid,filled  is the volume of liquid in fluid container  101  when fluid container  101  is delivered to the wellsite, and P filled , T filled , P emptied , and V emptied  are the pressures and volumes of the gas when fluid container  101  is delivered (filled) and picked up (emptied). Thus, by measuring the change in pressure of gas  113  with a known volume of liquid  115  in a fluid container  101  of known volume, the amount of liquid  115  dispensed may be calculated. In some embodiments, the temperature term may be ignored, assuming that gas  113  is air, and the temperature of the gas is the same as the temperature of the surrounding environment both when fluid container  101  is filled and when the measurement is taken. 
         [0019]    In some embodiments, the hydrostatic pressure of liquid within the container may instead be utilized. As depicted in  FIG. 4 , fluid container  201  may include hydrostatic pressure sensor  205  which is submerged within liquid  215 . In some embodiments, hydrostatic pressure sensor  205  may be coupled to extension arm  217 , extending from the top of fluid container  201 . In some embodiments, extension arm  217  may be, for example, a wire or cable from which hydrostatic pressure sensor  205  is suspended. In some embodiments, hydrostatic pressure sensor  205  may include or be coupled to a weight to, for example, ensure hydrostatic pressure sensor  205  is able to sink to the bottom of any liquid  215  which may be in fluid container  201 . In some embodiments, the weight distribution of hydrostatic pressure sensor  205  may be such that hydrostatic pressure sensor  205  lays horizontally on the bottom of fluid container  201 . In other embodiments, as depicted in  FIG. 5 , fluid container  201  may include hydrostatic pressure sensor  205  which is mounted to the bottom of fluid container  201 . 
         [0020]    In embodiments measuring the hydrostatic pressure of liquid  215 , the height of the column of liquid  215  may be calculated from the differential pressure measured by hydrostatic pressure sensor  205 . Assuming that liquid  215  is incompressible, and thus the density of liquid  215  is constant, the height of liquid  215  above hydrostatic pressure sensor  205  may be calculated according to: 
         [0000]    
       
         
           
             
               h 
               = 
               
                 p 
                 
                   g 
                   · 
                   ρ 
                 
               
             
             , 
           
         
       
     
         [0000]    where h is the height of liquid  215  above hydrostatic pressure sensor  205 , p is the differential pressure measured by hydrostatic pressure sensor  205 , g is the gravitational acceleration, and ρ is the density of the fluid. One having ordinary skill in the art with the benefit of this disclosure will understand that the density of liquid  215  may be calculated from its specific gravity, and that the density of liquid  215  may vary based on, for example, the temperature of liquid  215 . By knowing the height of liquid  215  and the geometry of fluid container  201 , the volume of liquid  215  in fluid container  201  may be calculated according to: 
         [0000]        V=∫   0   h   A ( z ) dz,    
         [0000]    where V is the volume of liquid  215  above hydrostatic pressure sensor  205 , z is a distance in the direction of h (up) from hydrostatic pressure sensor  205 , and A(z) is the cross-sectional area of fluid container  201  at a distance z. By comparing the volume of liquid  215  measured at drop off and the volume of liquid  215  measured at pick-up, the volume of liquid  215  dispensed can be readily calculated. 
         [0021]    With regards to  FIG. 1 , in some embodiments, control unit  111  may include a computer or microcontroller to make the relevant previously described calculations. In some embodiments, control unit  111  may further include equipment for transmitting the calculated volume change to portal  117  as depicted in  FIG. 1 . In some embodiments, control unit  111  may communicate by wireless communication equipment  119  to wireless communication equipment  121  at portal  117 . In some embodiments, control unit  111  may communicate with portal  117  via satellite uplink  123  utilizing satellite  125 . In some embodiments, satellite uplink  123  may be one of Globalstar or Iridium LEO networks. In some embodiments, control unit  111  may connect to a land-based communications network, such as cellular, GSM, LTE, HSPA, CDMA, etc. to communicate with portal  117 . In some embodiments, control unit  111  may connect wirelessly to the internet to communicate its measurements to portal  117 . 
         [0022]    Once measurements are received at portal  117 , portal  117  may initiate a billing request from the client. In some embodiments, each fluid container  101  may be assigned a unique identifier such as a serial number to allow portal  117  to associate the fluid container  101  with a specific client, worksite, liquid type, distributor, etc. Portal  117  may, in some embodiments, aggregate this data to identify the client, worksite, container, liquid type, distributor, and automatically generate a bill for the client based on the amount of liquid dispensed as calculated by control unit  111 . In some embodiments, a user input on control unit  111  may cause control unit  111  to measure pressure differential and transmit the information to portal  117 . 
         [0023]    In other embodiments, rather than utilizing pressure sensor  105  to determine the amount of liquid dispensed from fluid container  101 , a load cell may be used to determine the weight of fluid container  101 , and thus derive the amount of liquid dispensed by comparing the weight of fluid container  101  at delivery and when picked up. Knowing the density or specific gravity of the liquid, the volume dispensed may be calculated. Such a load cell may be positioned on flatbed  10  or as a part of fluid container  101 . 
         [0024]    The foregoing outlines features of several embodiments so that a person of ordinary skill in the art may better understand the aspects of the present disclosure. Such features may be replaced by any one of numerous equivalent alternatives, only some of which are disclosed herein. One of ordinary skill in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. One of ordinary skill in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.

Technology Category: h