Patent Publication Number: US-9410414-B2

Title: Environmentally sealed system for fracturing subterranean formations

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to systems for fracturing subterranean formations, and more particularly, relating to environmentally sealed systems for fracturing subterranean formations. 
     BACKGROUND OF THE INVENTION 
     Hydraulic fracturing of subterranean formations, also called fracking, is well known. Hydraulic fracturing is a process that uses high pressure fracturing fluid that is pumped into a well to cause the rock formation of the well to separate apart, or fracture, creating pockets within the rock formation. Hydraulic fracturing allows production of oil and gas from areas where other well completion technologies are limited or not possible. 
     Generally a fracturing fluid is mixed with a proppant and then pumped into a well to create high pressures within the well. After the cracks develop in the rock formations due to the high pressure, the proppant flows into the crack and lodges in place. The proppant stops the crack from closing once the high pressure is released. 
     The fracturing fluids used in hydraulic fracturing represent varying levels of volatility. Volatility is classified by the vapor pressure and flash point of the fluid. Typically, fluids with a vapor pressure less than 2 pounds per square inch (“psi”) at 100° F. and a flash point greater than 10° F. above ambient temperatures are considered to be non-volatile. Non-volatile fracturing fluids may be open to the environment and therefore may be blended with proppant at a continuous rate through the use of open blenders. Examples of non-volatile fluids include water, low vapor pressure hydrocarbons, and methanol/water mixtures. Volatile fracturing fluids, however, must be processed in an environmentally sealed blender. Environmentally sealed, as used in this context, means that the processing equipment is sufficiently sealed to prevent leakage of gases and particulates from within the processing equipment under normal operating pressures of the equipment. 
     Until now the only environmentally sealed mixers available were enclosed mixers that only allow for batch processing of fracturing fluid and proppant rather than continuous processing of these materials. Examples of volatile fluids which must be processed in environmentally sealed equipment include liquid carbon dioxide and liquid petroleum gases such as propane or butane. 
     While non-volatile fracturing fluids are much easier to work with, due to the ability to continuously process the fracturing fluid and proppant in an open blender, a number of additional fluid characteristics must be taken into account which may make the use of volatile fluids more desirable. These characteristics include density, viscosity, vapor pressure, flash point, pH, surface tension, compatibility with formation, reservoir fluid, and cost.  FIG. 1  shows relative costs of several common fracturing fluids.  FIG. 2  shows relative safety risks of several common fracturing fluids. And  FIG. 3  shows relative environment impact risks of several common fracturing fluids. 
     While the devices heretofore fulfill their respective, particular objectives and requirements, they do not provide an environmentally sealed system for fracturing subterranean formations as such there exists and need for a system for fracturing subterranean formations, which substantially departs from the prior art, and in doing so provides an apparatus primarily developed for the purpose of fracturing subterranean formations in a manner that allows continuous blending and pumping of fracturing fluid and proppant in a manner that is sealed from the environment. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing disadvantages inherent in the known types of systems for fracturing subterranean formations including hydraulic fracturing systems now present in the prior art, the present invention provides a new environmentally sealed system for fracturing subterranean formations. 
     In general, in one aspect, an environmentally sealed apparatus for fracturing subterranean systems is provided. The apparatus for fracturing subterranean systems includes an environmentally sealed proppant hopper comprising a variable proppant regulator, an environmentally sealed blender comprising a blender inlet and a blender outlet, and a high pressure pump comprising a high pressure pump inlet and a high pressure pump outlet; wherein the blender inlet comprises a fracturing fluid inlet, a fracturing vapor outlet, a proppant inlet, and a proppant vapor outlet; the environmentally sealed proppant hopper is connected to the blender inlet through a proppant transfer connection; and the blender outlet is fluidically connected to the high pressure pump inlet. 
     In general, in another aspect, an environmentally sealed system for fracturing subterranean systems is provided. The system for fracturing subterranean systems includes an environmentally sealed fracturing fluid source, an environmentally sealed proppant source, an environmentally sealed proppant hopper comprising a variable proppant regulator, an environmentally sealed blender comprising a blender inlet and a blender outlet, a high pressure pump comprising a high pressure pump inlet and a high pressure pump outlet, and a well head; wherein the environmentally sealed fracturing fluid source is fluidically connected to the blender inlet through a fracturing fluid supply connection and a fracturing vapor recovery connection, the environmentally sealed proppant source is connected in a flow relationship with the environmentally sealed proppant hopper through a proppant supply connection and a proppant vapor recovery connection, the environmentally sealed proppant hopper is connected to the blender inlet through a proppant transfer connection, the blender outlet is fluidically connected to the high pressure pump inlet, and the high pressure pump is outlet fluidically connected to the well head. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated. 
     Numerous objects, features and advantages of the present invention will be readily apparent to those of ordinary skill in the art upon a reading of the following detailed description of presently preferred, but nonetheless illustrative, embodiments of the present invention when taken in conjunction with the accompanying drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of descriptions and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawings illustrate by way of example and are included to provide further understanding of the invention for the purpose of illustrative discussion of the embodiments of the invention. No attempt is made to show structural details of the embodiments in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. Identical reference numerals do not necessarily indicate an identical structure. Rather, the same reference numeral may be used to indicate a similar feature of a feature with similar functionality. In the drawings: 
         FIG. 1  is a table showing the relative fluid costs for different types of fracturing fluids; 
         FIG. 2  is a table showing the relative safety risk for different types of fracturing fluids; 
         FIG. 3  is a table showing the relative environmental impact for different types of fracturing fluids; 
         FIG. 4  is a schematic view of the environmentally sealed system for fracturing subterranean systems constructed in accordance with the principles of the present invention; 
         FIG. 5  is a schematic view of the environmentally sealed system for fracturing subterranean systems, showing or illustrating the combination with an additional system for fracturing subterranean systems; 
         FIG. 6  is an isometric view of a conventional vented storage tank; 
         FIG. 7  is a schematic view of an environmentally sealed storage tank; 
         FIG. 8  is a side view of the environmentally sealed system for fracturing subterranean systems, illustrating the proppant delivery system; 
         FIG. 9  is a cross-sectional view of the environmentally sealed proppant hopper, showing the variable proppant regulator; and 
         FIG. 10  is a schematic view of the system used for calculation of required proppant flow. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 4 through 9 , there is illustrated a new environmentally sealed apparatus and system for fracturing subterranean systems  10  in accordance with an embodiment of the present invention. The main components of the environmentally sealed apparatus  10  are a proppant hopper  12 , a blender  14 , and a high pressure pump  16 . The proppant hopper  12  and the blender  14  are environmentally sealed. The proppant hopper  12  is connected to the blender  14  through a proppant transfer connection  18 . The proppant transfer connection  18  is also environmentally sealed, and permits proppant to flow from the proppant hopper  12  to the blender  14 . 
     Proppant is to be understood as any solid particulate material that may be suspended in fluid. Proppant may be either natural or synthetic. Proppants may also be coated with a resin to modify one or more characteristics of the proppant. Commonly used proppants include sand, ceramics, bauxites, and other specialty compositions. 
     The blender mixes the proppant with a fracturing fluid that is supplied to the inlet of the blender through a fracturing fluid supply connection  20 . Typical fracturing fluids include water; hydrocarbon fluids, such as diesels, kerosenes, condensates, and mineral oils; liquefied gases, such as carbon dioxide; liquefied petroleum gases, such as propane and butane; and combinations thereof. The fracturing fluid may include additives such as viscosity modifiers, friction modifiers, antibacterialcides, emulsifiers, demulsifiers, breakers, or any other additive known in the art. 
     The fracturing fluid supply connection  20  connects the inlet  22  of the blender  14  to a fracturing fluid source  24  in a manner that permits the fracturing fluid to flow from the fracturing fluid source  24  to the inlet  22  of the blender  14 . The fracturing fluid source  24  will be chosen based on the type of fracturing fluid to be used. Fracturing fluid sources  24  may include one or more pressurized tanks, non-pressurized tanks, reservoirs, or any other fracturing fluid sources known in the art. Non-pressurized tanks may or may not be environmentally sealed. 
       FIG. 5  shows an exemplary non-pressurized tank  46  which is not environmentally sealed. The non-environmentally sealed tank  46  includes a vent tube  48  which allows excess gases and vapors to vent from the non-environmentally sealed tank  46 . The tank may have one or more tank inlet valves  50  and one or more tank outlet valves  52 . 
       FIG. 6  shows exemplary environmentally sealed tanks  54 . The environmentally sealed tanks  54  may be connected to one or more vent lines  56  that may be joined together thereby forming a vent manifold  58 . The vent manifold  58  may be connected, via a vapor control valve  60 , to a vapor return line  62 . The flow of fracturing fluid from the environmentally sealed tanks  54  creates a reduced pressure within the environmentally sealed tanks  54  that assists in evacuating excess gases and vapors from the blender  14  through the one or more vent lines  56 . The vapor control valve  60  may be a conventional valve or a one-way valve to prevent vapors from returning back through the vapor return line  62  and to the blender  14 . The vent manifold  58  may also be connected to a flare  64  to permit flaring of vapor within the vent manifold  58 . A purge valve  66  may be connected to control the flow of vapor from the vent manifold  58  to the flare  64 . 
     The environmentally sealed tanks  54  may also be connected to an inlet manifold  68 . The inlet manifold  68  may be connected to the environmentally sealed tanks  54  through inlet valves  70 . The inlet manifold  68  may also be connected to a main inlet valve  72  to control flow to the inlet manifold  68 . An external fracturing fluid source may be connected to the main inlet valve  72  for filling the environmentally sealed tanks  54 . During the filling of the environmentally sealed tanks  54  the external fracturing fluid source may be connected to the vent manifold  58  by a filling vent valve  69 . The filling vent valve  69  selectively permits or prevents flow of vapors from the vent manifold  58 . 
     The environmentally sealed tanks  54  may also be connected to an outlet manifold  74 . The outlet manifold  74  may be connected to the environmentally sealed tanks  54  through outlet valves  76 . The outlet manifold  74  may also be connected to a main outlet valve  78  to control flow from the outlet manifold  68  to the blender  14 . The outlet manifold  74  may further be connected to a secondary outlet valve  80  to control flow from the outlet manifold  74  during draining or transfer of the contents of the environmentally sealed tanks  54 . 
     Embodiments utilizing environmentally sealed tanks  54  for a fracturing fluid source  24  will preferably be connected to a fracturing vapor outlet  26  which connects the inlet  22  of the blender  14  to the fracturing fluid source  24 . The fracturing vapor outlet  26  allows any particles, vapors or gases within the blender  14  to be transferred to the fracturing fluid source  24 . Allowing the particles, vapors, or gases within the blender  14  to be transferred to the fracturing fluid source  24  reduces pressure buildup in the blender  14 . 
     In many instances it is beneficial to supply an additive to the fracturing fluid and proppant during the blending process. The additives may be viscosity modifiers, friction modifiers, antibacterialcides, emulsifiers, demulsifiers, breakers, or any other additive known in the art. In embodiments allowing for addition of additive to the fracturing fluid and proppant in the blender  14 , an additive source  28  is connected to an additive inlet  30  connected to the inlet  22  or the outlet  40  of the blender  14 . 
     The additive source  28  will be chosen based on the type of additive to be used. Additive sources  28  may include one or more pressurized tanks, non-pressurized tanks, reservoirs, or any other additive sources known in the art. Non-pressurized tanks may or may not be environmentally sealed. 
     In many embodiments the proppant hopper  12  is connected to a proppant source  34  through a proppant conveyance system  36  that is environmentally sealed. The proppant source  34  may be one or more unsealed containers, environmentally sealed containers, piles, pits, or any other proppant sources known in the art. Environmentally sealed containers may or may not be pressurized. The proppant source  34  will preferably be an environmentally sealed non-pressurized container. 
     Once the proppant, fracturing fluid and optional additives are mixed together in the blender  14 , the mixture is transferred through a blender outlet  40  to the high pressure pump  16 . From the high pressure pump  16 , the mixture is transferred through a high pressure pump outlet  42  to a well head  44 . In some embodiments it may be beneficial for the output streams of two or more systems for fracturing subterranean systems, or parts thereof, to join together at some point prior to entering the well head.  FIG. 7  schematically shows an embodiment of the present invention joined together with a conventional fracturing system between the high pressure pump  16  and the well head  44 . 
     Now with particular reference to  FIGS. 8 and 9 , the proppant deliver and mixing system  82  of the present invention will be described. The proppant is stored in the proppant source  34 . The proppant is delivered from the proppant source  34  to the proppant conveyance system  36  through a proppant source outlet  86 . The proppant may be carried by a proppant transfer  88  to an intermediate hopper  90 . The proppant transfer  88  may be open or may be environmentally sealed. It is preferred that the proppant transfer  88  be environmentally sealed to contain dust particles from the proppant. The sealed proppant transfer  88  will be connected to a transfer vapor return  92  to return particles, dust and gases from the proppant transfer to the proppant source  34 . The proppant hopper  12  may be connected to a hopper vapor return  38  to return particles, dust and gases from the proppant hopper  12  to the proppant source  34 . 
     Once the proppant is in the intermediate hopper  90 , an inert gas may be injected into the intermediate hopper  90  through the lower inert gas injection port  94 . The inert gas functions to purge the proppant of air. The inert gas may be carbon dioxide, nitrogen, or any other suitable inert gas known in the art. 
     The proppant is raised to a level above the proppant hopper  12  by a proppant lift  96 . The proppant lift  96  will preferably be an auger. At the upper section  98  of the proppant hopper  12 , an inert gas may be injected through the upper inert gas injection port  100 . The inert gas assists the proppant perform a sealing function for the proppant hopper  12 . The inert gas may be carbon dioxide, nitrogen, or any other suitable inert gas known in the art. 
     Between the upper section  98  of the proppant hopper  12  and the proppant transfer connection  18 , through which proppant enters the blender  14 , the proppant hopper  12  includes a variable proppant regulator  104  and a hopper seal  106 . The variable proppant regulator  104  is designed to allow adjustment to the amount of proppant flow. The variable proppant regulator will preferably be of a design which incorporates a regulating orifice  108  in the variable proppant regulator  104  which is movable relative to an exit orifice  110  of the hopper  12 . The regulating orifice  108  will allow a maximum proppant flow when the regulating orifice  108  and the exit orifice  110  are aligned. Movement of the variable proppant regulator  104  relative to the exit orifice  110  results in a reduced overlap of the regulating orifice  108  and the exit orifice  110  thereby reducing the amount of proppant flow. 
     The variable proppant regulator  104  will preferably be continuously or incrementally adjustable between a maximum overlap of the regulating orifice  108  and the exit orifice  110 , referred to as a fully open position, and no overlap of the regulating orifice  108  and the exit orifice  110 , referred to as a closed position. The regulating orifice  108  will preferably provide a static seal between the hopper  12  and the blender  14  when in the closed position. The static seal provided by the regulating orifice  108  in the closed position seals proppant from entering the proppant transfer connection  18  from the hopper  12 . The static seal provided by the regulating orifice  108  in the closed position also preferably seals particles, vapors, or gases from entering the proppant transfer connection  18  from the blender  14 . 
     The hopper seal  106  will preferably be a solid door type of seal. The hopper seal is movable relative to the hopper  12  so that when the hopper seal  106  is in an open position there is substantially no overlap between hopper seal  106  and the flow passage for the proppant through the hopper  12 . When the hopper seal  106  is in an closed position there is substantially full overlap between hopper seal  106  and the flow passage for the proppant through the hopper  12  thereby sealing particles, vapors, or gases from entering the upper section  98  of the proppant hopper  12 . The hopper seal  106  may also be an overlapping orifice type of seal similar to the variable proppant regulator  104 . 
     During operation of the blender  14 , the flow of proppant through the proppant hopper  12  provides a pressure seal for the blender  14 . The pressure seal is achieved by calculating the theoretical vapor flow through a proppant hopper  12  filled with proppant of the type being supplied to the blender  14  in a static condition and then ensuring that the velocity of the proppant through the proppant hopper  12  is greater than or equal to the calculated flow. Vapor flow through the proppant in a static condition can be calculated by the following formula: 
     
       
         
           
             q 
             = 
             
               
                 
                   - 
                   k 
                 
                 μ 
               
               ⁢ 
               
                 
                   ∇ 
                   P 
                 
                 . 
               
             
           
         
       
     
     Where q is the flux meaning the discharge per unit area with units of length per time, μ is viscosity, k is the permeability of the medium and ∇ is the pressure gradient vector. Providing a per unit area value, the above formula is a derivation of the well know formula for calculation of the flow of a fluid through a porous medium known as Darcy&#39;s law and shown below: 
     
       
         
           
             Q 
             = 
             
               
                 
                   - 
                   kA 
                 
                 μ 
               
               ⁢ 
               
                 
                   
                     ( 
                     
                       
                         P 
                         b 
                       
                       - 
                       
                         P 
                         a 
                       
                     
                     ) 
                   
                   L 
                 
                 . 
               
             
           
         
       
     
     Where Q is the rate of flow, μ is viscosity, k is the permeability of the medium, A is the cross-sectional area of the porous medium, L is the length of the porous medium, P a  is the Pressure at point a, and P b  is the pressure at point b. The system for application of Darcy&#39;s law is shown in  FIG. 10 . 
     The mass flow rate of the proppant, q m , through the hopper  12  may be calculated by the formula
 
 q   mr   =q   fs   ·C,  
 
where q fs  is the flow rate of the mixture through the outlet  40  of the blender  14  and C is the proppant flow rate into the inlet  22  of the blender  14 . The volumetric flow rate of the proppant, q vfr , through the hopper  12  may be calculated by the formula
 
                 q   vfr     =       q   mr     BD       ,         
where BD is the bulk density of the proppant. The minimum cross sectional area of the proppant flow to equalize vapor flow from the blender  14  to the proppant flow into the blender  14  may be calculated by the formula
 
     
       
         
           
             
               A 
               ⁢ 
               
                   
               
               ⁢ 
               
                 ∅ 
                 min 
               
             
             = 
             
               
                 
                   q 
                   vfr 
                 
                 q 
               
               . 
             
           
         
       
     
     The permeability is determined by the gas being examined and the proppant utilized. Proppant is graded by how it passes through a sieve. For example, a proppant labeled as 20/40 will pass through a sieve that has twenty openings per square inch would not pass through a sieve that has forty openings per square inch. The effective permeability can be changed by adding a fluid into the pores of the proppant. For this reason, the upper section  98  of the proppant hopper  12  may also include a permeability altering fluid addition port  102 . A permeability altering fluid may be injected into the proppant hopper  12  through the permeability altering fluid addition port  102  to further assist the proppant perform a sealing function for the proppant hopper  12 . The permeability altering fluid will preferably be a non-volatile fluid. The permeability altering fluid may include water, low vapor pressure hydrocarbons, and methanol/water mixtures. 
     The differential pressure across the hopper  12  will be the maximum vapor pressure of the fluid used at the highest potential ambient temperature. The ambient temperature will change from geographic location and time of year. The fracturing vapor outlet  26  functions to minimize the potential pressure drop across the proppant hopper  12  by reducing the pressure in the blender  14 . This allows the flow of proppant through the hopper  12  to seal the hopper  12  against leakage of gases in the proppant transfer connection  18  and blender  14 . 
     Inert gas may also be injected into the upper section  98  of the proppant hopper  12  through the upper inert gas injection port  100  to increase the pressure in the upper section  98  of the proppant hopper  12 . The increased pressure in the upper section  98  of the proppant hopper  12  reduces the pressure drop across the proppant hopper  12 . The reduced pressure drop across the proppant hopper  12  improves the efficiency of the seal created by the flow of proppant through the proppant hopper  12 . 
     Once the minimum cross sectional area of the proppant flow has been determined for a given desired output from the blender  14 , the variable proppant regulator  104  will preferably be adjusted to provide an orifice overlap between the regulating orifice  108  and the exit orifice  110  that provides an opening of the minimum cross sectional area. The use of the variable proppant regulator allows the proppant hopper  12  to be used with many various proppant flows. 
     The blender  14  may be a centrifugal type blender, a barrel type blender, or any other type of blender known in the art. Fracturing fluid enters the blender  14  through the fracturing fluid supply connection  20 . The optional additive enters the blender  14  through the additive inlet  30 . The fracturing vapor outlet  26  allows any particles, vapors or gases within the blender  14  to be transferred away from the blender  14 . Once the proppant, the fracturing fluid, and the optional additives are mixed in the blender  14  they are transmitted from the blender  14  through the outlet  40  of the blender  14   
     A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.