Patent Publication Number: US-2011048695-A1

Title: Manifold and system for servicing multiple wells

Description:
FIELD OF THE INVENTION 
     Embodiments of the invention relate to servicing multiple wells with a fluid and, more particularly, to manifolds and valving therein for selectively accessing the wells and further to minimize the erosive effects of stimulation fluids therein. 
     BACKGROUND OF THE INVENTION 
     There are an increasing number of subterranean hydrocarbon reservoirs which are accessed using multiple wells for optimizing production therefrom. The wells and wellheads connected thereto are often closely spaced, the wellbores being angled downwardly and radially outwardly to access as much as the reservoir as possible. 
     Many or all of multiple pay zones in such reservoirs may be characterized by low permeability or other characteristics which require stimulation of one or more of the wells for increasing production therefrom. During selective stimulation of the wells, which may include fracturing operations performed on one well, wireline operations may be also be performed on other wells, such as to shift wellbore access from one zone to another zone. To consolidate pumping equipment, such as pumpers and proppant supply for use in fracturing, a large common manifold has been employed to connect a fracturing fluid inlet selectively to one or more of the wellheads of the multiple wells. Thus, multiple wells can be stimulated simultaneously with multiple trains of pumpers and manifolds. 
     Prior art manifolds are characterized by a plurality of adjacent flow blocks forming a single main manifold having a large bore for connecting fluid delivery lines to each wellhead. Large, full bore gate valves are located inline with the manifold bore between each adjacent flow block for isolating the adjacent flow blocks from one another. For example, for a manifold having a 7 inch bore, 7 inch valves, typically gate valves, are spaced inline between each adjacent flow block, fit flange to flange with ring seals and bolted together. Thus, when a valve or a seal is leaking, it is challenging and cumbersome to manipulate the single large manifold sufficiently to arrange to lift the compromised valve clear of the manifold. Further, it is difficult to part the flanges and remove, service and replace the compromised valve and ring seals without causing damage to the seals. 
     The need to maintenance the manifold and valves is exacerbated by the erosive nature of stimulation fluids flowing therethrough during stimulation operations. The stimulation fluids typically have high fluid flow rates caused to flow at high velocity from the single large bore manifold through like-sized outlets. The high velocity flow results in significant wear to the manifold and manifold valves, as well as to downstream equipment. 
     The addition of proppant, such as sand, to fracturing fluids is known to cause severe erosion. Generally, the proppant is added to the fracturing fluid at the pumpers and thus upstream equipment, such as the fluid pumpers, are also vulnerable to the erosive effects of the proppant-laden fracturing fluids passing therethrough. 
     Currently, it is known and common to stockpile replacement manifold components, including new flow blocks and valves, onsite and ready for replacement as the job proceeds. It is also known to have replacement fluid pumpers on standby to assume stimulation fluid delivery while active pumpers are taken offline for refurbishing. On large jobs, it is not uncommon to have ten or more pumpers on site, the redundancy required to maintain simultaneous and continuous stimulation despite the increased costs. 
     The flexibility of selection of wells which can be serviced by the prior art manifold is compromised by the valves located inline in the bore of the manifold. Wells can only be serviced in series. Once a gate valve has been closed in the bore to isolate a well, all of the wells fluidly connected to the manifold downstream of the closed gate valve are also isolated. Therefore should one wish to service wells which are remotely fluidly connected from one another it may not be possible to do so without delivering fluids to the intervening wells. 
     There is clearly a need in the industry for more cost effective and robust apparatus and methods for the delivery of stimulation fluids selectively to multiple wells and to improve the flexibility with which wells may be selected. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to an apparatus, system and method of selectively servicing two or more wells concurrently. A fluid, such as a fracturing fluid is pumped from pumping units through a manifold that is fluidly connected to the two or more wells. The velocity of the fluid is reduced as the fluid travels from the pumping unit to the manifold and is further reduced as the fluid travels from the manifold to each of the two or more wells. The reduction of the velocity of the fluid reduces the erosive effects of the fluid on the manifold and other equipment, prolonging the operational life thereof. 
     In a broad aspect of the invention, a manifold for delivering a fluid for selectively servicing two or more wells has a manifold body having a live bore formed therethrough, the live bore having a live bore cross-sectional area. An inlet is fluidly connected to the live bore for receiving the fluid therein. Two or more distributors are also fluidly connected to the live bore for distributing the fluid to each of the two or more well. Each distributor has two or more outlets fluidly connected to one well of the two or more wells for delivery of fluids thereto, and each outlet has an outlet bore with an outlet cross-sectional area. Valves are positioned in each outlet bore of the two or more outlets for selectively isolating the fluid from one or more of the two or more wells. The total outlet cross-sectional area for each of the two or more distributors is greater than the live bore cross-sectional area for reducing the velocity of the fluid in the two or more outlets. 
     In another broad aspect of the invention, a system for servicing two or more wells accessing a formation, the wells having wellheads attached thereto, has a manifold, a source of a fluid, fluidly connected to the inlet; and fluid connections between the two or more outlets of each of the two or more distributions blocks and one wellhead of the two or more wells. The manifold can comprise a bore formed therethrough for receiving a fracturing fluid, an inlet fluidly connected to the bore for delivering the fracturing fluid to the bore, two or more outlets fluidly connected to the bore, at least one outlet fluidly connected to one of the two or more wells, and valves operatively connected between the manifold bore and each of the one or more wells for isolating the fracturing fluid from one or more of the two or more wells. 
     The system pumps the fluid from the fluid source to the manifold, the fluid flowing unimpeded through the main bore of the manifold block for delivery to the two or more outlets of each of the two or more distribution blocks. 
     When two or more valves of one or more of the two or more distribution blocks are actuated to an open position, the fluid flows through the main bore is delivered to the one or more wells fluidly connected thereto, and when the two or more valves of one or more of the two or more distribution blocks are actuated to a closed position, the one or more wells fluidly connected thereto are isolated from the fluid flowing through the main bore. 
     In another broad aspect of the invention, a method for replacing or repairing a valve in a manifold for selectively accessing two or more wells, the manifold having two or more distribution flow blocks, each distribution flow block fluidly connected to a main manifold bore and having two or more outlets fluidly connected to one well of the two or more wells for delivery of fluids thereto, each outlet having an outlet bore and a valve removeably secured thereto, involves discontinuing flow of fluid to the manifold bore, disconnecting the removeable connectors between the outlet and the valve, reconnecting a new or repaired valve to the outlet; and reestablishing the flow of fluid to the manifold bore. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  is a schematic representation of a prior art system including at least one pumper for delivering fluid to a prior art manifold fluidly connected to two or more wells; 
         FIG. 1B  is a schematic representation of a manifold according to an embodiment of the invention; 
         FIG. 2  is a more detailed longitudinal, partial sectional view of the manifold of  FIG. 1B , gate valves having been removed from facing outlets for clarity; 
         FIG. 3  is an exploded partial cross-sectional view according to  FIG. 2  illustrating a distribution flow blocks, a receiving flow block and flanged connectors for connecting therebetween; 
         FIG. 4  is a longitudinal partial cross-sectional view of the manifold of  FIG. 2 , illustrating a common contiguous live bore and outlets fluidly connected thereto for delivery fluid to multiple wellheads; 
         FIG. 5  is a cross-sectional view of the receiving flow block of  FIG. 3 , illustrating inlets for receiving from a fluid source; 
         FIG. 6  is a cross-sectional view of the distribution flow block of  FIG. 3 , illustrating outlets for fluidly connecting to a wellhead; 
         FIG. 7  is a cross-sectional view of the flanged connector of  FIG. 3 ; 
         FIG. 8  is a cross-sectional view of an end distribution flow block, illustrating three outlets and an inline flow connection for connection to a second manifold or for release of fluid from the live bore; 
         FIG. 9  is a schematic representation of a main manifold and two slave manifolds according to an embodiment of the invention; 
         FIG. 10  is a partial cross-sectional view of a slave manifold according to  FIG. 9 ; 
         FIG. 11  is a schematic site layout of the prior art system of  FIG. 1A  in use for a fracturing operation and having pumpers, a sandbox for providing proppant and blenders for adding and mixing the proppant to the fracturing fluid before delivery to the prior art manifold; 
         FIG. 12A  is a schematic site layout of an embodiment of a system having pumpers, proppant supply and blenders for a multi-well stimulation system, the erosive proppant being provided in a proppant supply system parallel to the high rate of fracturing fluids from the fluid system, the proppant supply and fluid systems combining at the wellhead; 
         FIG. 12B  is a schematic site layout of an embodiment of a system having pumpers, proppant supply and blenders for a multi-well stimulation system, the erosive proppant being provided in a first concentration to the fracturing fluid and being provided in a second concentration, different that the first concentration, in a parallel proppant only supply system, the first and second concentrations combining at the wellhead; 
         FIG. 13A  is a schematic site layout of an embodiment wherein a fracturing fluid pumping unit is fluidly connected to a main manifold and a slave manifold for delivering fracturing fluid using a first fluid path, and a slurry pumping unit fluidly connected directly to a wellhead for delivering a slurry of proppant and fluid using a second fluid flow path; 
         FIG. 13B  is a partial side cross-sectional view of the embodiment of  FIG. 11A , illustrating fracturing fluid entering the fracturing head in opposing arrangement while the proppant slurry is delivered inline with a radial axis of the fracturing head; and 
         FIG. 14  is a schematic site layout of an embodiment wherein the slurry pumping unit is capable of servicing two wellheads concurrently. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1A , in a prior art multi-well stimulation operation, a prior art manifold  10  is utilized for fluidly connecting one or more stimulation fluid sources  12 , typically pumpers, to a wellhead  14  of each of a plurality of wells  16  so as to permit selectively accessing two or more of the wells  16  concurrently. The prior art manifold  10  comprises a plurality of large, full-bore sized inline gate valves  18  therein for isolating selected wells  16 . The manifold  10  receives the stimulation fluid from the one or more pumpers  12  at high velocity for selective delivery through large outlets  20 , maintaining the high velocity of the fluid delivered therefrom, to the selected wells  16 . Applicant notes that when one or more of the gate valves  20  are closed for isolating any of the wells  16  from the manifold  10 , any wells  16  fluidly connected downstream from the closed gate valve  18  are isolated. Thus, selection of wells  16  to be serviced is not flexible. Further, it has been noted that erosion occurs in both the valves  18  and the manifold  10 , particularly as the high velocity, high flow rate fluid turns to exit at high velocity from large diameter outlets  20 . 
     In the prior art, to lessen the fluid velocity and rate of erosion, the combined pumping capacity, typically from the plurality of pumpers  12 , was routed through a plurality of parallel fluid supply lines  22  (four shown) to the manifold  10 . The gate valves  18  dividing the manifold bore were then closed or opened selectively for isolating some wellheads  14  and for directing fluids to others. To lessen the fluid velocity and rate of erosion associated therewith, a plurality of parallel fluid delivery lines  24  (four shown) were connected from the outlets  20  to the wellhead  14 . Applicant notes however that the parallel delivery lines  24  do not significantly reduce erosion that occurs at the connection of the large diameter outlets  20  to the large diameter manifold  10 . 
     As shown in  FIG. 1B , embodiments of the invention utilize a manifold  200  having a manifold body  201  which comprises an open, live bore  202  formed therethrough. Distributors  204  comprising two or more outlets  206  are fluidly connected to the live bore  202  for fluid connection to each wellhead  14 . As described in greater detail below, the two or more outlets  206  in each distributor  204  have a total outlet cross-sectional area which is greater than a cross sectional area of the live bore  202  for reducing the velocity of the fluid at the outlets  206 . Further, valves  208  for isolating the wells are positioned in each of the outlets  206 . The valves  208  in the outlets  206  are therefore not only subjected to lower velocity flows for reducing wear, but are also positioned outside the manifold&#39;s live bore  202  for easier access for maintenance, repair or replacement. This is particularly advantageous when the stimulation fluid is a fracturing fluid carrying a proppant, which is highly erosive at the high velocity. 
     An additional advantage of positioning the valves  208  in the outlets  206  is that there is greater flexibility in selecting wells  16  for servicing. As each well  16  is independently connected to the live bore  202  of the manifold  200 , one or more wells  16  can be isolated from the manifold bore  202  and the fluids therein without affecting the delivery of fluid to any of the other wells  16 . 
     Further, as each outlet  206  can have a cross-sectional area which is smaller than a cross-sectional area of the manifold bore  202 , the valves  208  therein can also be reduced in size. Smaller valves are easier to remove for repair or replacement. Typically, the valves  208  are connected to the outlets  206  through removable connectors such as flanged connections  207 . 
     When valves  208  require removal for replacement or repair, the flow of fluid to the live bore  202  is discontinued. The removable connections  207  between the outlet  208  and the valve  208  to be removed are disconnected and the valve  208  is removed. Thereafter, a new valve  208  or a repaired valve  208  is provided at the outlet  206  and the removable connectors  207  reconnected therebetween. Once the valve  208  has been replaced, the flow of fluids is reestablished through the live bore  202 . Typically, the manifold  200  is pressure tested following replacement of the valve  208  to ensure the manifold  200  is capable of withstanding stimulation pressures. 
     While embodiments of the invention are suitable for delivery of a variety of stimulating fluids, embodiments of the invention are generally described herein in the context of a fracturing operation. Particular advantages are obtained when using embodiments of the invention for delivering fracturing fluids which comprise a particulate proppant P therein. 
     In greater detail, as shown in  FIGS. 2-4 , a body  201  of the manifold  200  comprises a receiving flow block  210  having one or more inlets  212  for receiving a fracturing fluid F from the fluid source  12 , such as a pumping unit. The receiving flow block  210  has a bore  214  formed therethrough to which the one or more inlets  212  are fluidly connected. The manifold body  201  further comprises two or more distribution flow blocks  220 , each of the distribution flow blocks having a bore  222  formed therethrough and comprising one of the two or more distributors  204  having the two or more outlets  206  fluidly connected to the bore  222 . The bore  214  of the receiving flow block  210  and the bores  222  of the distribution flow blocks  220  are fluidly connected to one another for forming the live bore  202 . 
     In embodiments the flow blocks are connected using flanged connectors  230 , each of the flanged connectors  230  having a bore  232  formed therethrough for forming the live bore  202 . 
     Together, the receiving flow block  210 , the distribution flow blocks  220 , and the flanged connectors  230  structurally form the manifold body  201 . 
     With reference to  FIG. 5 , and in greater detail, in an embodiment the receiving flow block  210  comprises the receiving bore  214  extending longitudinally therethrough. The one or more inlets  212  which extend radially from the receiving bore  214  comprise four inlets  212  positioned in an opposing arrangement. That is, each inlet  212  is positioned directly opposite another inlet  212  so that fracturing fluid F incoming through the opposing inlets  212  will impinge for reducing the velocity of the fluid F. The reduction in velocity further aids in reducing the erosive effects of the fracturing fluid F within the manifold  200  and downstream equipment. 
     The receiving bore  214  has an internal diameter RB ID  defining a total cross-sectional area RB XA . Each of the one or more inlets  212  has an internal diameter I ID , defining an inlet cross-sectional area I XA . The total cross-sectional area of the longitudinal receiving bore RB XA  is greater than the total combined inlet cross-sectional areas I XA  for reducing the velocity of the fracturing fluid F entering the receiving bore  214 . 
     With reference to  FIG. 6 , each distribution flow block  220  has a corresponding longitudinal distribution bore  222  having an internal diameter of DB ID . The one or more outlets  206  extending radially outwardly from the distribution bore  222  comprise four outlets  206 . Each outlet  206  has an internal diameter O ID  defining an outlet cross-sectional area O XA . A total combined outlet cross-sectional area O XA  is greater than the live bore cross-sectional area LB XA . Accordingly, as the fracturing fluid F travels from the relatively smaller live bore cross-sectional area LB XA  into the relatively larger outlet cross-sectional area O XA , the velocity of the fracturing fluid F decreases. 
     With reference to  FIG. 7 , the longitudinal connector bore  232  of the connector  230  has an internal diameter CB ID . In an embodiment, the internal diameter CB ID  of the connector bore  232  is substantially the same as the internal diameter DB ID  of the distribution bore  222  and the internal diameter RB ID  of the receiving bore  214  to minimize areas where erosion may occur. 
     The connector bore  232 , the receiving bore  214  and the distribution bores  222 , form the common, contiguous live bore  202  having a cross-sectional area LB XA . 
     In an embodiment, as shown in  FIG. 8 , in distribution blocks  220   e  positioned at opposing ends of the manifold  200 , one of the outlets  206  comprises an inline flow connection  224  for discharging up to about 25% of the fracturing fluid within the live bore  202  for minimizing wear and erosion. 
     As one of skill in the art will appreciate, the velocity of the fracturing fluid F, as it travels at an initial pumping velocity from the pumpers  12  through the inlets  212  to the larger cross-sectional receiving flow bore  214 , is reduced. Thereafter as the fluid F travels from the distribution flow blocks  220  and to the total larger cross-sectional area of the outlets  206 , the velocity is reduced again. The cumulative reduction in velocity of the fracturing fluid F minimizes the erosive effects of the abrasive fracturing fluid F on the manifold  200  and on other downstream well equipment. 
     For example, a typical 7 inch fracturing flow system, uses 7 inch inlet flow lines  212  to the inlet receiving block  210  having a total inlet cross-sectional area I XA , of about 39 square inches. Four—4 1/16 inch outlet lines  206  from the distribution flow block  220  have an outlet cross-sectional area O XA  of about 13 square inches per outlet  2106 , or a total outlet cross-sectional area O XA  of about 52 square inches. 
     Applicant believes that the smaller valves  208 , such as 4 inch valves, fit within the smaller, individual outlets  206  are more reliable than the large prior art valves. Embodiments of the invention permit use of the smaller, more reliable valves  208 , yet permit a total outlet cross-sectional area O XA  greater than that of the common contiguous live bore  202  permitting velocity reduction. 
     Table 1 summarizes typical velocity reductions observed according to embodiments of the invention. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 FLUID VELOCITIES (FT/SEC) IN VARIOUS I.D.&#39;s 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 VALVE DIA. 
                 VEL. © 4 M 3 /MIN. 
                 VEL. © 5 M 3 /MIN. 
               
               
                   
                   
               
               
                   
                 7 1/16″ 
                 8.6 FPS 
                 10.8 FPS 
               
               
                   
                 4 1/16″ 
                  26 FPS 
                 32.5 FPS 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 VALVE DIA. 
                 VEL. © 3 M 3 /MIN. 
               
               
                   
                   
               
               
                   
                 3 1/16″ 
                 34.3 FPS 
               
               
                   
                   
               
               
                   
                 MANIFOLD I.D. 
                 VEL. © 16 M 3 /MIN. 
               
               
                   
                   
               
               
                   
                 7 1/16″ 
                 34.4 FPS 
               
               
                   
                   
               
               
                   
                 NOTES: 
               
               
                   
                 EACH WELL FED BY 4 LINES 
               
               
                   
                 EACH MANIFOLD FED BY 4 LINES 
               
               
                   
                 MANIFOLD IS 7 1/16″ DIA. 
               
               
                   
                 ALL VALVES ARE 4 1/16″ DIA 
               
               
                   
                 ALL LINES ARE 4 1/16″ DIA 
               
               
                   
                 PRESSURE RATING IS 10,000 PSI 
               
               
                   
                 QUICK CHANGE OF ALL PARTS 
               
            
           
         
       
     
     As shown, the velocity of a fracturing fluid F entering a 7 1/16″ diameter live bore  202  of the manifold  200 , through four 4 1/16″ inlet lines  212  at an initial pumping velocity of 16 cubic meters per minute (m3/min), is reduced from the initial pumping velocity to 34.4 feet per second (fps) in the live bore  202 . 
     In a manifold  200  having fracturing fluid F flowing through the live bore  202  therein at 3 m 3 /min and four outlets  206  at each distribution block  220 , each outlet  206  and valve  208  therein having a diameter of 3 1/16″, the velocity at each of the four outlets  206  is 34.4 fps. 
     In a manifold  200  having fracturing fluid F flowing through the live bore  202  therein at 4 m 3 /min and four outlets  206  at each distribution block  220 , each outlet  206  and valve  208  therein having a diameter of 4 1/16″, the velocity at each of the four outlets  206  is 26 fps. If the outlet  206 /valve  208  diameter is increased to 7 1/16″, the velocity is reduced to 8.6 fps. 
     In a manifold  200  having fracturing fluid F flowing through the live bore  202  therein at 5 m 3 /min and four outlets  206  at each distribution block  220 , each outlet  206  and valve  208  therein having a diameter of 4 1/16″, the velocity at each of the four outlets  206  is 32.5 fps. If the outlet  206 /valve  208  diameter is increased to 7 1/16″, the velocity is reduced to 10.8 fps. 
     Having reference to  FIGS. 9 and 10 , in an embodiment, the manifold  200  further comprises a main manifold  200   m , fluidly connected to one or more slave manifolds  200   s . The one or more slave manifolds  200   s  are substantially identical in structure to the main manifold  200   m , having a slave receiving block  210   s  fluidly connected to the main manifold  200   m  for receiving fracturing fluid F therefrom. Two or more slave distribution blocks  220   s , each comprising two or more slave distributors  204  having two or more slave outlets  206   s , deliver fracturing fluid F to two or more of the plurality of wells  16 . The slave manifold  200   s  has a live bore  202   s  formed therethrough as described for the main manifold  200   m . In an embodiment, the slave receiving block  210   s  is fluidly connected to and receives fracturing fluid F at slave inlets  212   s  from one or more of the outlets  206  of end distributions blocks  220   e  of the main manifold  200   m.    
     As shown in  FIG. 9 , as an example, the system is capable of being fluidly connecting to eight wellheads  14 , labeled A-H, for servicing using the main manifold  200   m  and two slave manifolds  200   s . The eight wells  16  can be stimulated simultaneously, depending on pumper capability or isolated independently for stimulation or for servicing as necessary, such as for replacing lines or changing a zone for the next fluid treatment. 
     In embodiments, each of the main and slave manifolds  200   m ,  200   s  can be shorter in length, the overall manifold system being capable of servicing the same number of wells  16  as would be serviced using a single, large manifold  200 . Advantageously, the shorter length manifolds  200   m ,  200   s  are particularly suited to sites where space constraints are an issue. 
     Having reference again to  FIGS. 8 ,  9  and  10 , the inline flow connection  224  from the end distribution blocks  220   e  positioned at opposing ends of the main manifold  200   m  and the slave manifolds  200   s , besides having the advantage of providing a discharge from the live bores  202   m ,  202   s  of the main and slave manifolds  200   m ,  200   s , also provide a convenient drain/bleed or methanol access point. 
     Fracturing Operations 
     Having reference to  FIG. 11 , a prior art system of delivering a fracturing fluid F to a plurality of wells  16  as shown in  FIG. 1A , incorporates a prior art manifold  100 . Proppant P, such as sand from a sandbox, is conveyed to one or more blenders  26  for mixing with fluid W, usually water from local sources at ambient conditions. The proppant-laden fluid F is delivered to the plurality of pumpers  12  for pressurizing to stimulation pressures. To lessen fluid velocity and the rate of erosion, the combined pumping capacity is routed through the parallel fluid supply lines  22  (four shown) to the prior art manifold  10 . From the manifold  10 , valves  18  dividing the manifold  10  are opened for directing fracturing fluids F and proppant P contained therein to the selected wellhead  14  or closed for isolating a wellhead  14  or wellhead  14  downstream therefrom from the fracturing fluid F. Again, for lessening fluid velocity and the rate of erosion, the fracturing fluid F is also routed through parallel fluid delivery lines  24  (four shown) to the wellhead  14 . 
     In embodiments of the invention, issues related to the erosive nature of the proppant P present in stimulation fluids, such as fracturing fluids F, are minimized using systems and methodology for delivery thereof. As one of skill in the art will appreciate, while embodiments of the invention are described herein using a manifold  200  according to an embodiment of the invention to achieve the combined benefits thereof, the systems and methods described can also be practiced using prior art manifolds  10 . 
     Utilizing systems and methods according to embodiments of the invention, proppant P can be delivered directly to the wellheads  14  for mixing with fluid F at the wellheads  14 , can be delivered to the pumpers  12  for forming the fracturing fluid F therein for delivery to a manifold  10 ,  200  for subsequent delivery to the wellheads  14  or can be delivered to both the manifold  200  and the wellheads  14  for mixing at the wellheads  14 . 
     In the case where proppant P is delivered to the pumpers  12  for delivery to the manifold  200 , the fracturing fluid F is delivered as described for the prior art as shown in  FIG. 1A . Use of the novel manifold  200  according to embodiments of the invention, results in decreases in velocity of the proppant-laden fluid F flowing therethrough and through downstream equipment for reducing erosion therein as previously described and discussed. 
     As shown in  FIG. 12 , in the case where proppant P is delivered directly to the wellheads  14  for mixing with the fluid F, the proppant P is blended with a fluid W, typically water for forming a proppant slurry PS. The proppant slurry PS is delivered to one or more proppant pumpers  12   p , designated for proppant use, for pressurizing to stimulation pressures. The proppant slurry PS is thereafter delivered through delivery lines  28  to the wellheads  14 . Simultaneously, fracture fluid F, absent proppant P, is pressurized in a plurality of pumpers  12  for delivery to the manifold  200  and to the wellheads  14  as previously described. 
     Embodiments which deliver proppant slurry PS directly to the wellheads  14  eliminate any erosion in pumpers  12 , in the manifold  200  and in the valves  108  in the manifold outlets  206 . The proppant pumpers  12  however are placed at higher risk for erosion of pumping equipment therein. 
     In an embodiment of the invention, proppant P is provided to both the fluid pumpers  12  and to the proppant pumpers  12   p . In this embodiment, proppant P is provided to the fluid pumpers  12  at a first concentration PS 1  and is provided to the proppant pumpers  12   p  at a second concentration PS 2  which is higher than the first concentration. The fracturing fluid F with proppant P and the proppant slurry PS are mixed at the wellheads  14  to a final concentration or design load of proppant P for delivery to the wells  16 . 
     In embodiments, the first proppant concentration PS 1  is lower than concentrations which result in significant erosion and thus, the fluid pumpers  12  can last much longer before servicing, unlike in the prior art where servicing is typically performed periodically during well stimulation. 
     Further, as the fracturing fluid F flowing through the manifold  200  and downstream components is less erosive, the rate of flow can be increased without increased erosion. With increased flow rates, the number of flow lines required to deliver the same volume of fracturing fluid F can be decreased. 
       FIGS. 13A and 14 , illustrate a reduced number of supply lines  22  from the pumping unit  12  to the main manifold  200   m  and from the main manifold  200   m  to a slave manifold  200   s . Further, the fluid delivery lines  24  from the main manifold  200   m  and the slave manifold  200   s  to the wellheads  14  can also be reduced. In an embodiment as shown, two supply lines  22  and two delivery lines  24  are used through which fluid flows at twice the volumetric throughput as the previously described embodiments. In the case shown in  FIG. 13A , proppant slurry PS is provided through a single supply line  28  directly to a single wellhead  14  and in the case of  FIG. 14 , proppant slurry PS is provided through two supply lines  28 , directly to two wellheads  14 . 
     Accordingly, embodiments which utilize only two fluid delivery lines  22  to the wellheads  14  utilize only two outlet ports  206  and two valves  208  in each distribution flow block  220 . The remaining outlets  206  remain unused and can be fit with valves  208  which are closed to isolate the outlets  206  or alternatively the outlets  206  can be plugged. Alternatively, the distributions blocks  220  can be manufactured having fewer outlets  206  for this purpose. The reduction of flow lines  22 , 24  required to conduct fracturing fluid from the pumping units  12  to the well  16  contribute to reducing capital expense, faster setup, faster pressure testing, due in part to fewer components and connections, and a reduction in equipment clutter onsite. 
     As shown in  FIG. 13B , at a selected wellhead  14 , fracturing fluid F, without proppant P or at the first proppant concentration PS 1 , is injected from the manifold  200  through delivery lines  24  into a fracturing head  30  in the wellhead  14  through inlets  32  on opposing sides of the fracturing head  30 . The opposing arrangement acts to cause the fluid streams to impinge and absorb energy before the fracturing fluid F is directed downhole by the fracturing head  30 . 
     Where the proppant slurry PS is provided to the wellhead  14  from the proppant pumpers  12   p  through delivery line  28 , either at the full design concentration or at the second concentration PS 2 , the proppant slurry PS from the proppant pumpers  12   p  is added to a port  34  of the fracturing head  30  to combine with the fracturing fluid F injected therein through the opposing inlets  32 . The net result is that the design load of proppant P is provided in the overall combined fluid flow downhole. 
     For example, two 4-inch fluid delivery lines  24  from the manifold  200  coupled to opposing inlets  32  at the fracturing head  30  can deliver the fracturing fluid F from the manifold  200  at a flow rate of about 7 m 3 /min. Proppant slurry PS, at concentrations of up to 800 kg/m 3 , pumped from the proppant pumpers  12   p  through a single 3-inch delivery line  28  connected to the port  34  of the fracturing head  30 , delivers the proppant slurry PS at a flow rate of about 3 m 3 /min, which is substantially less than the flow rate of the fracturing fluid F. In embodiments, the port  34 , is inline with a bore of the fracturing head  30  and thus minimizes even further any erosive effects at the fracturing head  30 . 
     Applicant is aware that the concentration of proppant PS 2  in the proppant slurry PS might be four times the concentration of proppant PS 1  in the fracturing fluid F and yet remain pumpable. Where the proppant pumpers  12   p  pump proppant slurry PS having a high concentration of proppant P, the velocity is reduced. Further, as the high concentration proppant slurry PS contains very low fluid levels, it is not responsible for providing operational levels of fracturing fluid F. Thus, it becomes feasible to expend energy to warm up the smaller amounts of ambient water used to prepare the proppant slurry PS to enhance chemical mixing during the preparation of the proppant slurry PS at the blender  26 .