Abstract:
A hydraulic fracturing system includes an electrically powered pump that pressurizes fluid, which is piped into a wellbore to fracture a subterranean formation. System components include a fluid source, an additive source, a hydration unit, a blending unit, a proppant source, and a fracturing pump. The system includes heaters for warming hydraulic fluid and/or lube oil. The hydraulic fluid is used for operating devices on the blending and hydration units. The lube oil lubricates and cools various moving parts on the fracturing pump.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of, and claims priority to and the benefit of, co-pending U.S. Provisional Application Ser. No. 62/156,307, filed May 3, 2015 and is a continuation-in-part of, and claims priority to and the benefit of co-pending U.S. patent application Ser. No. 13/679,689, filed Nov. 16, 2012, the full disclosures of which are hereby incorporated by reference herein for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present disclosure relates to hydraulic fracturing of subterranean formations. In particular, the present disclosure relates to an electrical hydraulic fracturing system having heaters for heating hydraulic fluid. 
         [0004]    2. Description of Prior Art 
         [0005]    Hydraulic fracturing is a technique used to stimulate production from some hydrocarbon producing wells. The technique usually involves injecting fluid into a wellbore at a pressure sufficient to generate fissures in the formation surrounding the wellbore. Typically the pressurized fluid is injected into a portion of the wellbore that is pressure isolated from the remaining length of the wellbore so that fracturing is limited to a designated portion of the formation. The fracturing fluid slurry, whose primary component is usually water, includes proppant (such as sand or ceramic) that migrate into the fractures with the fracturing fluid slurry and remain to prop open the fractures after pressure is no longer applied to the wellbore. A primary fluid for the slurry other than water, such as nitrogen, carbon dioxide, foam, diesel, or other fluids is sometimes used as the primary component instead of water. Typically hydraulic fracturing fleets include a data van unit, blender unit, hydration unit, chemical additive unit, hydraulic fracturing pump unit, sand equipment, wireline, and other equipment. 
         [0006]    Traditionally, the fracturing fluid slurry has been pressurized on surface by high pressure pumps powered by diesel engines. To produce the pressures required for hydraulic fracturing, the pumps and associated engines have substantial volume and mass. Heavy duty trailers, skids, or trucks are required for transporting the large and heavy pumps and engines to sites where wellbores are being fractured. Each hydraulic fracturing pump is usually composed of a power end and a fluid end. The hydraulic fracturing pump also generally contains seats, valves, a spring, and keepers internally. These parts allow the hydraulic fracturing pump to draw in low pressure fluid slurry (approximately 100 psi) and discharge the same fluid slurry at high pressures (over 10,000 psi). Recently electrical motors controlled by variable frequency drives have been introduced to replace the diesel engines and transmission, which greatly reduces the noise, emissions, and vibrations generated by the equipment during operation, as well as its size footprint. 
         [0007]    On each separate unit, a closed circuit hydraulic fluid system is often used for operating auxiliary portions of each type of equipment. These auxiliary components may include dry or liquid chemical pumps, augers, cooling fans, fluid pumps, valves, actuators, greasers, mechanical lubrication, mechanical cooling, mixing paddles, landing gear, and other needed or desired components. This hydraulic fluid system is typically separate and independent of the main hydraulic fracturing fluid slurry that is being pumped into the wellbore. At times a separate heating system is deployed to heat the actual hydraulic fracturing fluid slurry that enters the wellbore. The hydraulic fluid system can thicken when ambient temperatures drop below the gelling temperature of the hydraulic fluid. Typically waste heat from diesel powered equipment is used for warming hydraulic fluid to above its gelling temperature. For diesel powered equipment, this typically allows the equipment to operate at temperatures down to −20° C. However, because electrically powered fracturing systems generate an insignificant amount of heat, hydraulic fluid in these systems is subject to gelling when exposed to low enough temperatures. These temperatures for an electric powered fracturing system typically begin to gel at much higher temperatures of approximate 5° C. 
       SUMMARY OF THE INVENTION 
       [0008]    Disclosed herein is an example of a hydraulic fracturing system for fracturing a subterranean formation, and which includes at least one hydraulic fracturing pump fluidly connected to the well and powered by at least one electric motor, and configured to pump fluid slurry into the wellbore at high pressure so that the fluid slurry passes from the wellbore into the formation, and fractures the formation. The system also includes a variable frequency drive connected to the electric motor to control the speed of the motor, wherein the variable frequency drive frequently performs electric motor diagnostics to prevent damage to the at least one electric motor, and a working fluid system having a working fluid, and a heater that is in thermal contact with the working fluid. Other electric motors on the equipment that do not require variable or adjustable speed (which generally operate in an on or off setting, or at a set speed), may be operated with the use of a soft starter. The working fluid can be lube oil, hydraulic fluid, or other fluid. In one embodiment, the heater includes a tank having working fluid and a heating element in the tank in thermal contact with the working fluid. The heating element can be an elongate heating element, or a heating coil, or a thermal blanket that could be wrapped around the working fluid tank. The system can further include a turbine generator, a transformer having a high voltage input in electrical communication with an electrical output of the turbine generator and a low voltage output, wherein the low voltage output is at an electrical potential that is less than that of the high voltage input, and a step down transformer having an input that is in electrical communication with the low voltage output of the transformer. The step down transformer can have an output that is in electrical communication with the heater. In an example, more than one transformer may be used to create multiple voltages needed for the system such as 13,800 V three phase, 600 V three phase, 600 V single phase, 240 V single phase, and others as required. In an example, the pumps are moveable to different locations on mobile platforms. 
         [0009]    Also described herein is another example of a hydraulic fracturing system for fracturing a subterranean formation and that includes a pump having a discharge in communication with a wellbore that intersects the formation, an electric motor coupled to and that drives the pump, a variable frequency drive connected to the electric motor that controls a speed of the motor and performs electric motor diagnostics, and a working fluid system made up of a piping circuit having working fluid, and a heater that is in thermal contact with the working fluid. The working fluid can be lube oil or hydraulic fluid, which is circulated using an electric lube pump through the hydraulic fluid closed circuit for each piece of equipment. In one embodiment, on each separate unit, a closed circuit hydraulic fluid system can be used for operating auxiliary portions of each type of equipment. These auxiliary components may include dry or liquid chemical pumps, augers, cooling fans, fluid pumps, valves, actuators, greasers, mechanical lubrication, mechanical cooling, mixing paddles, landing gear, conveyer belt, vacuum, and other needed or desired components. This hydraulic fluid system can be separate and independent of the main hydraulic fracturing fluid slurry that is being pumped into the wellbore. At times a separate heating system is deployed to heat the actual hydraulic fracturing fluid slurry that enters the wellbore. The hydraulic fracturing system can optionally include a turbine generator that generates electricity for use in energizing the motor. In an example, the pump is a first pump and the motor is a first motor, the system further including a trailer, a second pump, and a second motor coupled to the second pump and for driving the second pump, and wherein the first and second pumps and motors are mounted on the trailer. In another embodiment, a single motor with drive shafts on both sides may connect to the first and second pumps, wherein each pump could be uncoupled from the motor as required. The hydraulic fracturing system can further include a first transformer for stepping down a voltage of electricity from an electrical source to a voltage that is useable by the pump&#39;s electrical motor, and a second transformer that steps down a voltage of the electricity useable by the pump&#39;s electrical motor to a voltage that is usable by the heater. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0011]      FIG. 1  is a schematic of an example of a hydraulic fracturing system. 
           [0012]      FIGS. 2-4  are schematics of examples of step down transformers and hydraulic fluid heaters for use with the hydraulic fracturing system of  FIG. 1 . 
           [0013]      FIG. 5A  is a perspective view of an example of a tank with a heating element for warming hydraulic fluid for use with the hydraulic fracturing system of  FIG. 1 . 
           [0014]      FIG. 5B  is a side view of an alternate embodiment of a heating element for use with the tank of  FIG. 5A . 
       
    
    
       [0015]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0016]    The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude. 
         [0017]    It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
         [0018]      FIG. 1  is a schematic example of a hydraulic fracturing system  10  that is used for pressurizing a wellbore  12  to create fractures  14  in a subterranean formation  16  that surrounds the wellbore  12 . Included with the system  10  is a hydration unit  18  that receives fluid from a fluid source  20  via line  22 , and also selectively receives additives from an additive source  24  via line  26 . Additive source  24  can be separate from the hydration unit  18  as a stand-alone unit, or can be included as part of the same unit as the hydration unit  18 . The fluid, which in one example is water, is mixed inside of the hydration unit  18  with the additives. In an embodiment, the fluid and additives are mixed over a period of time to allow for uniform distribution of the additives within the fluid. In the example of  FIG. 1 , the fluid and additive mixture is transferred to a blender unit  28  via line  30 . A proppant source  32  contains proppant, which is delivered to the blender unit  28  as represented by line  34 , where line  34  can be a conveyer. Inside the blender unit  28 , the proppant and fluid/additive mixture are combined to form a fracturing slurry, which is then transferred to a fracturing pump system  36  via line  38 ; thus fluid in line  38  includes the discharge of blender unit  28 , which is the suction (or boost) for the fracturing pump system  36 . Blender unit  28  can have an onboard chemical additive system, such as with chemical pumps and augers. Optionally, additive source  24  can provide chemicals to blender unit  28 ; or a separate and standalone chemical additive system (not shown) can be provided for delivering chemicals to the blender unit  28 . In an example, the pressure of the slurry in line  38  ranges from around 80 psi to around 100 psi. The pressure of the slurry can be increased up to around 15,000 psi by pump system  36 . A motor  39 , which connects to pump system  36  via connection  40 , drives pump system  36  so that it can pressurize the slurry. After being discharged from pump system  36 , slurry is injected into a wellhead assembly  41 ; discharge piping  42  connects discharge of pump system  36  with wellhead assembly  41  and provides a conduit for the slurry between the pump system  36  and the wellhead assembly  41 . In an alternative, hoses or other connections can be used to provide a conduit for the slurry between the pump system  36  and the wellhead assembly  41 . Optionally, any type of fluid can be pressurized by the fracturing pump system  36  to form injection fracturing fluid that is then pumped into the wellbore  12  for fracturing the formation  14 , and is not limited to fluids having chemicals or proppant. Examples exist wherein the system  10  includes multiple pumps  36 , and multiple motors  39  for driving the multiple pumps  36 . Examples also exist wherein the system  10  includes the ability to pump down equipment, instrumentation, or other retrievable items through the slurry into the wellbore. 
         [0019]    An example of a turbine  44  is provided in the example of  FIG. 1  and which receives a combustible fuel from a fuel source  46  via a feed line  48 . In one example, the combustible fuel is natural gas, and the fuel source  46  can be a container of natural gas or a well (not shown) proximate the turbine  44 . Combustion of the fuel in the turbine  44  in turn powers a generator  50  that produces electricity. Shaft  52  connects generator  50  to turbine  44 . The combination of the turbine  44 , generator  50 , and shaft  52  define a turbine generator  53 . In another example, gearing can also be used to connect the turbine  44  and generator  50 . An example of a micro-grid  54  is further illustrated in  FIG. 1 , and which distributes electricity generated by the turbine generator  53 . Included with the micro-grid  54  is a transformer  56  for stepping down voltage of the electricity generated by the generator  50  to a voltage more compatible for use by electrical powered devices in the hydraulic fracturing system  10 . In another example, the power generated by the turbine generator and the power utilized by the electrical powered devices in the hydraulic fracturing system  10  are of the same voltage, such as 4160 V so that main power transformers are not needed. In one embodiment, multiple 3500 kVA dry cast coil transformers are utilized. Electricity generated in generator  50  is conveyed to transformer  56  via line  58 . In one example, transformer  56  steps the voltage down from 13.8 kV to around 600 V. Other stepped down voltages can include 4,160 V, 480 V, or other voltages. The output or low voltage side of the transformer  56  connects to a power bus  60 , lines  62 ,  64 ,  66 ,  68 ,  70 , and  72  connect to power bus  60  and deliver electricity to electrically powered end users in the system  10 . More specifically, line  62  connects fluid source  20  to bus  60 , line  64  connects additive source  24  to bus  60 , line  66  connects hydration unit  18  to bus  60 , line  68  connects proppant source  32  to bus  60 , line  70  connects blender unit  28  to bus  60 , and line  72  connects motor  39  to bus  60 . In an example, additive source  24  contains ten or more chemical pumps for supplementing the existing chemical pumps on the hydration unit  18  and blender unit  28 . Chemicals from the additive source  24  can be delivered via lines  26  to either the hydration unit  18  and/or the blender unit  28 . In one embodiment, the elements of the system  10  are mobile and can be readily transported to a wellsite adjacent the wellbore  12 , such as on trailers or other platforms equipped with wheels or tracks. 
         [0020]      FIG. 2  shows in a schematic form a portion of the system  10  of  FIG. 1  having the electric motor  39 . In one embodiment, this is for the hydraulic fracturing pump unit. Included with this example is a step down transformer  80  with a high voltage side HV in communication with line  72  via line  82 . Voltage is stepped down or reduced across transformer  80  to a low voltage side LV; which is shown in electrical communication with a load box  84  via line  86 . In one example, the high voltage side HV of transformer  80  is at around 600 V, and the stepped down (or low voltage side LV) is at around 240 V. Load box  84 , which operates similar to a breaker box, provides tie ins for devices that operate at the stepped down voltage. Line  88  provides communication between motor  39  and a heater system  90 , which is illustrated adjacent to motor  39  and is for heating lube oil that is used within pump  36  and other auxiliaries as needed (not shown). Heater system  90  includes a tank  91  in which oil can collect, and flow lines  92 ,  94  for directing lube oil between the tank  91  and a lube oil system  95  schematically shown with pump  36 . An example of a heating element  96  is shown disposed within tank  91  which receives current via line  88  from load box  84 . Electrical current flowing through the element  96  is converted into thermal energy, which is transferred to the lube oil and for heating the lube oil in the heater system  90 . The heater system  90  may be selectivity energized manually and/or include a thermal switch (not shown) to automatically turn the heating element  96  on and off at desired hydraulic fluid temperatures. Ground lines  100 ,  102 ,  106  provide connection between a ground side respectively of the heater system  96 , low voltage side of transformer  80 , pump  36 , and high voltage side of transformer  80  to ground G. Further illustrated in  FIG. 2  is an example of a variable frequency drive of (“VFD”)  107  and an A/C console (not shown), that control the speed of the electric motor  39 , and hence the speed of the pump  36 . 
         [0021]      FIG. 3  is a schematic example of a transformer  108  which steps down voltage of electricity within line  64  (which is on the low voltage or stepped down side of transformer  56  of  FIG. 1 ). Line  64  connects to transformer via line  110 . Line  112 , which connects to a low voltage side LV of transformer  108 , conducts electricity at the stepped down voltage to a load box  114 , which can provide a source point for use by components (not shown) in or associated with the hydration unit  18  that operate on electricity at the stepped down voltage. Branching from line  112  is line  116  which conducts electricity at the stepped down voltage to a load box  118 . Load box  118  defines an energy source point of energy for use by components (not shown) associated with the additive source  24  that operate on electricity at the stepped down voltage. In one example, load boxes  114  and  118  are replaced by a single load box. A hydraulic fluid heating system  122 , which is attached to the hydration unit  18 , and which includes a tank  123  in which hydraulic fluid used in operating components within hydration unit  18  is heated. An element  124  disposed within tank  123  operates similar to element  96  of  FIG. 2 . In another embodiment, element  124  is a heating blanket that wrapped around tank  123 . Hydraulic fluid is transmitted to and from tank  123  through flow lines  126 ,  128 , which connect to a hydraulically powered device  129  in hydration unit  18 . Hydraulically powered device  129  is a schematic representation of any equipment or devices in or associated with hydration unit  18  that are operated by hydraulic fluid. Thus hydraulic fluid heating system  122  warms hydraulic fluid used by hydraulically powered device  129  and prevents thickening of the hydraulic fluid. Line  120  provides electrical communication between element  124  so that it can be selectively energized to warm the hydraulic fluid. The selectivity can be manually operated and/or include a thermal switch to automatically turn the heating element  124  on and off at desired hydraulic fluid temperatures. In one embodiment, a secondary power source (not shown) such as an external generator, grid power, battery bank, or other power source at the same voltage as load box  84  can be connected directly into the as load box  84  to power the heating element without the entire microgrid being energized. This allows heating of the hydraulic fluid prior to starting the entire hydraulic fracturing fleet system. 
         [0022]    Electrical connection between load box  118  and additive source  24  is shown provided by line  132 . Also included with additive source  24  is a hydraulic fluid heating system  134  which includes a tank  135  for containing hydraulic fluid, and an element  136  within tank  135  for heating hydraulic fluid that is within tank  135 . Flow lines  138 ,  140  provide connectivity between tank  135  and a hydraulically powered device  141  shown disposed in or coupled with additive source  24 . Similar to hydraulically powered device  129 , hydraulically powered device  141  schematically represents hydraulically operated devices in or coupled with additive source  24 . Line  132  provides electrical communication to heating element  136  from load box  118 . Similar to hydraulic fluid heating system  122 , hydraulic fluid heating system  134  heats hydraulic fluid used by hydraulically powered device  141  so that the hydraulic fluid properties remain at designated operational values. As determined manually and/or include a thermal switch to automatically turn the heating element on and off at desired hydraulic fluid temperatures. Ground lines  143 ,  146 ,  148 ,  152  provide connection to ground G respectively from, hydraulic fluid heating system  34 , additive source  24 , low voltage side LV of transformer  108 , a hydraulic heating fluid system  122 , hydration unit  18 , and the high voltage HV side of transformer  108 . In one embodiment, a secondary power source (not shown) such as an external generator, grid power, battery bank, or other power source at substantially the same voltage as load box  118  and load box  114  can be connected directly into the as load box  118  and load box  114  to power the heating element without the entire microgrid being energized. This allows heating of the hydraulic fluid prior to starting the entire hydraulic fracturing fleet system. 
         [0023]      FIG. 4  illustrates a schematic example of a transformer  154  to provide electricity at a stepped down voltage to blender unit  28 . In one embodiment, transformer  154  and transformer  108  ( FIG. 3 ) are replaced by a single transformer. In this example, a high voltage side HV of transformer  154  connects to line  70  via line  156 . Voltage of electricity received by transformer  154  is stepped down and delivered to a low voltage side LV of transformer  154 . A load box  158  is in communication with the low voltage side LV of transformer  154  via line  160 . Electricity at load box  158  is communicated through line  162  to blender unit  28 . Line  162  selectively energizes an element  166  shown as part of hydraulic fluid heating system  168 . Selectivity energizing element  166  can be manually operated and/or include a thermal switch to automatically turn the heating element  166  on and off at desired hydraulic fluid temperatures. System  168  includes a tank  169  in which element  166  is disposed, and which receives hydraulic fluid from blender unit  28  via flow lines  170  and returns hydraulic fluid via flow line  172 . Flow lines  170 ,  172  connect to a hydraulically powered device  173  that is part of the hydration unit. Examples of hydraulically powered units that are powered by hydraulic fluid include chemical pumps, tub paddles (mixers), cooling fans, fluid pumps, valve actuators, and auger motors. Ground lines  174 ,  176 ,  180  provide connectivity through ground G from the heating system  168 , low voltage side LV of transformer  154 , and high voltage side HV of transformer  154 . In one embodiment, a secondary power source (not shown) such as an external generator, grid power, battery bank, or other power source at the same voltage as load box  158  can be connected directly into the load box  158  to power the heating element  166  without the entire microgrid being energized. This allows heating of the hydraulic fluid prior to starting the entire hydraulic fracturing fleet system. 
         [0024]      FIG. 5A  shows in perspective one example of a fluid heating system  181  and which includes a tank  182  having a housing  184  in which fluid F is contained. The fluid F can be hydraulic fluid or lube oil. The heating system  181  of  FIG. 5A  also includes an elongate heating element  186  shown projecting through a side wall of housing  184 . Heat element  186  is strategically disposed so that the portion projecting into tank  182  is submerged in fluid F. Line  188  provides electrical current to the element  186  and which may be from the stepped down voltage of one of the transformers  80  ( FIG. 2 ),  108  ( FIG. 3 ), or  154  ( FIG. 4 ). In this example, the housing  184  can be connected to ground G thereby eliminating the need for a ground line. Fluid heating system  181  of  FIG. 5A  provides an example embodiment to the heating systems of  FIGS. 2-4 .  FIG. 5B  illustrates an alternate example of the element  186 A and which is shown made up of a number of coils  190  that are generally coaxially arranged. Opposing ends of the coils  190  have contact leads  192 ,  194  attached for providing electrical connectivity through which an electrical circuit can be conducted and that in turn causes element  186 A to generate thermal energy that can be used in heating the hydraulic fluid or lube oil discussed above. 
         [0025]    The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, heating the fluids as described above can be accomplished by other means, such as heat exchangers that have fluids flowing through tubes. Moreover, electricity for energizing a heater can be from a source other than a turbine generator, but instead can be from a utility, solar, battery, to name but a few. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.