Abstract:
Downhole fracturing tools comprise upper and lower isolation devices and a housing disposed in between. The housing comprises a housing bore that is divided into two chambers isolated from each other within the housing bore. The upper bore is in fluid communication with a fluid injection line through which a fracturing fluid is pumped into the upper bore. The fracturing fluid flows down the upper bore, substantially parallel to a longitudinal length of the tool, and exits the tool through at least one port. The fracturing fluid then travels down the wellbore annulus. Returns from the fracturing fluid flow through a screen in the tool and up a return line that empties into the wellbore annulus above the upper isolation device.

Description:
BACKGROUND 
     1. Field of Invention 
     The invention is directed to fracturing tools for use in oil and gas wells, and in particular, to fracturing tools capable of directing fracturing fluid in a direction that is parallel to the casing before the fracturing fluid enters the perforations in the wellbore. 
     2. Description of Art 
     Fracturing or “frac” systems or tools are used in oil and gas wells for completing and increasing the production rate from the well. In deviated well bores, particularly those having longer lengths, fracturing fluids can be expected to be introduced into the linear, or horizontal, end portion of the well to frac the production zone to open up production fissures and pores therethrough. For example, hydraulic fracturing is a method of using pump rate and hydraulic pressure created by fracturing fluids to fracture or crack a subterranean formation. 
     In addition to cracking the formation, high permeability proppant, as compared to the permeability of the formation can be pumped into the fracture to prop open the cracks caused by a first hydraulic fracturing step. For purposes of this disclosure, the proppant is included in the definition of “fracturing fluids” and as part of well fracturing operations. When the applied pump rates and pressures are reduced or removed from the formation, the crack or fracture cannot close or heal completely because the high permeability proppant keeps the crack open. The propped crack or fracture provides a high permeability path connecting the producing wellbore to a larger formation area to enhance the production of hydrocarbons. 
     During fracturing operations, the fracturing fluid is directed from the fracturing tool at a high rate of flow and into a blast liner that redirects the fracturing fluid out of the fracturing tool and into the inner wall surface of the casing within in the well. The fracturing fluid then flows downward in the annulus of the well, i.e., between the outside of the fracturing tool or tool string to which the fracturing tool is connected and the inner wall surface of the wellbore or casing disposed in the wellbore, until it reaches the perforations in the wellbore that are to be packed with the fracturing fluid. As a result of the fracturing fluid flowing out of the fracturing tool and into the inner wall surface of the casing, the casing can be damaged, e.g., eroded by the fracturing fluid impacting the inner wall surface of the casing as soon as it leaves the fracturing tool. 
     SUMMARY OF INVENTION 
     Broadly, the fracturing tools disclosed herein comprise an upper isolation device, a lower isolation device, and a housing disposed between the upper and lower isolation devices. In one particular embodiment, the housing comprises a housing bore divided into an upper housing bore and lower housing bore in which the upper housing bore is isolated from the lower housing bore within the housing bore. In other words, fluid within the upper housing bore cannot flow directly into the lower housing bore within the housing bore itself. The upper housing bore comprises one or more ports, also referred to as frac slots, in an outer wall of the upper housing bore so that the upper housing bore is in fluid communication with a wellbore annulus, i.e., between the outer wall surface of the tool and the inner wall surface of the wellbore. 
     A fluid injection line is in fluid communication with the upper housing bore and releasably aligned or connected to a bore of a conduit string in which the tool is placed. The fluid injection line comprises a lowermost fluid injection line end that terminates within the upper housing bore above the port or ports. Thus, fracturing fluid pumped down the conduit string, through the fluid injection line, out of the lowermost end of the fluid injection line, into the upper housing bore, down the upper housing bore, in a direction that is substantially parallel to a longitudinal length of the tool, and out of the port into the wellbore annulus so fracturing operations can be performed. 
     Return fluid from the fracturing fluid flows into a screen disposed at a lowermost end of the housing above the lower isolation device. Thus, the screen is in fluid communication with the wellbore annulus. A fluid return line may be disposed within the housing bore which is in fluid communication with the screen. The fluid return line permits the return fluid to flow up through the tool and out of the tool into the wellbore annulus above the upper isolation device. In one particular embodiment, the fluid return line is not disposed within the housing bore, but instead is disposed outside the housing. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of one embodiment of the fracturing tool of the present invention. 
     
    
    
     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 
     Referring now to  FIG. 1 , in one specific embodiment, downhole tool  40  is shown disposed within casing  20  of a wellbore  22 . Casing  20  includes inner wall surface  24  and one or more perforations  26 . 
     In this embodiment, downhole tool  40  comprises upper isolation device  42  and lower isolation device  44 . Upper housing  46 , lower housing  48 , and screen  50  are disposed between upper isolation device  42  and lower isolation device  44 . 
     Screen  50  includes bore  52  and screen  50  can be releasably secured to lower isolation device  44  through any known device or method, for example, threads (not shown),or snap latch  54 . Lower isolation device  44  includes bore  56  that is in fluid communication through which lower portion  58  of screen  50  extends. As shown in  FIG. 1 , lower isolation device  44  contacts the inner wall surface  24  of casing  20  when lower isolation device  44  is placed in the set position. 
     In the set position, lower isolation device  44 , separates annulus  26  of wellbore  22  into two zones, middle zone  28  disposed above lower isolation device  44  and lower zone  29  disposed below lower isolation device  44 . Lower isolation device  44  is shown in the embodiment of  FIG. 1  as a sump packer, which is known in the art, however, lower isolation device  44  can be any other isolation device known in the art. 
     Similarly, in the set position, upper isolation device  42  separates annulus  26  of wellbore  22  into two zones, upper zone  30  disposed above upper isolation device  42  and middle zone  28  disposed below upper isolation device  42 . Lower isolation device  42  is shown in the embodiment of  FIG. 1  as a high pressure packer, which is known in the art, however, upper isolation device  42  can be any other isolation device known in the art. 
     Neither upper nor lower isolation devices  42 ,  44 , are required to form a leak-proof seals with the inner wall surface  21  of wellbore  20 . Fluid is permitted to flow between upper and lower isolation devices  42 ,  44  and the inner wall surface  24  of casing  20 , provided that the connections between upper and lower isolation devices  42 ,  44  and the inner wall surface  24  of casing  20  is sufficient to allow wellbore fluid to be transported from downhole tool  40 , into middle zone  28  and, subsequently, to upper zone  30  as discussed in greater detail below. 
     Upper isolation device  42  includes bore  43 . Upper housing  46  is disposed within bore  43 . Upper housing includes upper housing bore  60  and at least one frac slot  62 . Fracturing fluid injection line  63  is disposed within housing bore  60  and is in fluid communication with frac slot  62  such that fluid flows out of fluid injection line  63 , into housing bore  60 , and out of frac slot  62  in a vector that is parallel, or substantially parallel, to the longitudinal axis of downhole tool  40 . As used herein, “substantially parallel” means that the vector of the flow of fluid out of fluid injection line  63 , into housing bore  60 , and out of frac slot  62  is not changed by more than 45 degrees from the longitudinal axis of downhole tool  40  during transition from fluid injection line  63  into housing bore  60  or from housing bore  60  through frac slot  62 . In one specific embodiment, the flow of fluid out of fluid injection line  63 , into housing bore  60 , and out of frac slot  62  is not changed by more than 30 degrees from the longitudinal axis of downhole tool  40  during transition from fluid injection line  63  into housing bore  60  or from housing bore  60  through frac slot  62 . In another specific embodiment, the flow of fluid out of fluid injection line  63 , into housing bore  60 , and out of frac slot  62  is not changed by more than 15 degrees from the longitudinal axis of downhole tool  40  during transition from fluid injection line  63  into housing bore  60  or from housing bore  60  through frac slot  62 . Further, it is to be understood that the term “substantially parallel” also includes “parallel” in which the vector of the flow of fluid during transition from fluid injection line  63  into housing bore  60  or from housing bore  60  through frac slot  62 , is unchanged and, thus, parallel to the longitudinal axis of downhole tool  40 . 
     Also disposed within housing bore  60  is return line  64 . Return line  64  can include one-way check valve  66  to prevent backflow from occurring within return line  64 . In the embodiment shown in  FIG. 1 , return line  64  includes at least one concentric seal  68  to seal the outer wall surface of return line  64  with the inner wall surface of housing bore  60 . 
     Return line  64  is in fluid communication with wash pipe  70  that is disposed within lower housing bore  72 . Because concentric seals  68  isolate upper housing bore  60  from lower housing bore  72 , return fluids are forced to travel up the bore of wash pipe  70  and into return line  64 . 
     Return line  64  is also in fluid communication with upper zone  30  so that return fluid is transported into the wellbore above upper isolation device  42  where it can then travel to the surface of the well for recirculation as desired or needed for additional wellbore operations. 
     Lower housing  48  is secured to upper housing  46  through any method or device known to persons skilled in the art, such as through welding or threads (not shown). Lower housing  48  can also be secured to screen  50  through any method or device known to persons skilled in the art, such as through welding or threads (not shown). 
     In one particular operation of downhole tool  40 , a tubing string  90  is used to dispose downhole tool  40  into casing  20  of wellbore  22 . After disposition within casing  20 , upper and lower isolation devices  42 ,  44  are activated so that annulus  26  of wellbore  22  is divided into middle zone  28 , lower zone  29 , and upper zone  30 . Activation of upper and lower isolation devices  42 ,  44  can be accomplished using known methods. In one particular embodiment, upper isolation device  42  is set using setting tool  35 . 
     With particular reference to the arrows shown in  FIG. 1  that illustrate fluid flow through downhole tool  40 , after setting upper and lower isolation devices  42 ,  44  within casing  20 , fracturing fluid, such as proppant, is pumped work string  90  into and through fracturing fluid injection line  63  into housing bore  60  and out of frac slot  62 . The fracturing fluid then flows down annulus  26  within middle zone  28  until it reaches casing perforations  26 . The fracturing fluid then enters casing perforations  26  until fracturing operations are completed. 
     During operations, liquids such as water and, possibly gases, that are contained within the fracturing fluid are permitted to flow through screen  50 . The larger particulate matter within the fracturing fluid, such as gravel or sand, is not permitted to pass through screen  50 . This liquid or gas then mixes with other fluids contained within lower zone  29  of wellbore  22  and flows up wash pipe  70 , into return line  64 , through one-way check valve  66  and into upper zone  30  so that it can travel within wellbore  22  up toward the surface of wellbore  22 . After an amount of time as passed to fracture the wellbore as desired or necessary to stimulate hydrocarbon production from the well, fracturing fluid is no longer pumped downward through fracturing fluid injection line  63 . 
     As a result of the pathway of flow for the fracturing fluid through fracturing fluid injection line  63 , into housing bore  60 , and out of frac slot  62 , the fracturing fluid is ejected from downhole tool  40  into annulus  26  at a rate such that likelihood of erosion of casing  20  is lessened. This is because the flow of the fracturing fluid out of injection line  63  is substantially parallel to inner wall surface  24  of casing  20 . 
     In the embodiments discussed herein with respect  FIG. 1 , upward, toward the surface of wellbore  22 , is toward the top of  FIG. 1 , and downward or downhole (the direction going away from the surface of wellbore  22 ) is toward the bottom of  FIG. 1 . In other words, “upward” and “downward” are used with respect to  FIG. 1  as describing the vertical orientation illustrated in  FIG. 1 . However, it is to be understood that downhole tool  40  may be disposed within a horizontal or other deviated well so that “upward” and “downward” are not oriented vertically. 
     It is to be understood that the invention 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. For example, the upper and lower isolation devices can be any isolation device known in the art. Further, the inner wall surface of the wellbore may be disposed along an open-hole formation, along wellbore casing (as shown in  FIG. 1 ), or along a tubular member, including a packer or bridge plug, disposed within the wellbore casing or open hole formation. Moreover, the term “wellbore annulus” is to be understood to be the environment outside of the downhole fracturing tools, regardless of whether the downhole fracturing tool is actually disposed within a wellbore. Further, the wellbore may be cased or opened-hole. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.