Abstract:
A process and an apparatus for use in fluid fracturing of a well and the like is provided, the apparatus being a pumpable seat assembly for temporarily sealing a well casing comprising a generally cylindrical tube having an outer diameter and an inner diameter; a upper slip assembly and a lower slip assembly mounted on such cylindrical tube and adapted to selectively engage the well casing to anchor the pumpable seat assembly; an elastomeric packing element mounted on said cylindrical tube between the upper slip assembly and the lower slip assembly; and a dissolvable member positioned within the generally cylindrical tube for temporarily restricting a flow of fluids to the portion of the wellbore located below the pumpable seat assembly.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the field of vertical and horizontal well completion, and, more particularly, to a process for fracturing, stimulating and producing a wellbore without having to mill out and remove fracturing/bridge plugs and to a pumpable seat assembly for use with said process. 
       BACKGROUND OF THE INVENTION 
       [0002]    Oil and gas well are drilled to a depth in order to intersect a series of formations or zones which produce hydrocarbons. Often the drilled wells are cased with steel casing pipe and cemented to secure the casing in place. Hence, it is necessary to create a flow path from these cased producing zones to the surface of the wellbore. This is generally accomplished by stimulation processes such as fracturing using water, various chemicals and/or proppants. However, the steel and cement barrier needs to be first perforated with shaped explosive charges prior to fracturing the surrounding oil or gas reservoir. 
         [0003]    Depending on the number of producing zones in a particular reservoir, usually several elevation levels and/or lateral intervals will need to be fractured. Thus, it is common in the industry to use a temporary well completion plug which is generally set in the bore of the steel well casing with a setting tool just below the level or interval where the perforation of the steel and cement barrier and fracturing occurs. It is understood that these bridge or “frac plugs” can also be pumped down the well on an electric wireline, either by itself or in combination with the perforating gun assemblies. When the barrier is perforated, “frac fluids” and/or sand are pumped down to the perforations and into the reservoir to stimulate movement of the oil or gas. Use of the temporary plug prevents contamination of the already fractured levels below. 
         [0004]    Interval isolation and fracturing or stimulation can be performed on both vertical and horizontal wells with multiple planned intervals, often with multiple intervals and sometimes greater than 25 intervals per well at varying depths including sometimes greater than 6000 Meters Below Kelly Bushing (MKB). Bridge/frac plug technology for interval isolation for frac stimulation purposes is proven, effective, predictable and repeatable. 
         [0005]    Unfortunately, once all of the zones have been stimulated, these temporary plugs may prevent the flow of oil or gas to the surface. Thus, traditionally, these plugs need to be milled or drilled out using a drill bit using jointed pipe or coiled tubing. However, there are operational risks associated with this process and, further, this is a time consuming and costly procedure. Furthermore, it has been found that frac plugs having even a minimal amount of steel are difficult to drill during removal and can damage the drill bit. 
         [0006]    Coil tubing or jointed pipe intervention to mill out and remove the plugs on extended reach wells, e.g. lateral length exceeding 2500 m, is extremely costly, unpredictable and sometimes impossible due to metal to metal friction encountered sliding in the casing, creating what is known as coil tubing lock-up. In some cases, frac plugs that are not reachable due to friction lock up issues are left in the well (i.e., not milled out) and intervals left behind these frac plugs are expected to flow through a ¾ inch hole in the center of the frac plugs. Flow can sometimes be restricted by the number of frac plugs which were not accessible for mill-out due to the friction lock encountered. In some cases operations are exposed to such risks as sticking the coil tubing or bottom-hole assembly (BHA) in the well, resulting in fishing operations for pipe recovery. Fishing operations can cost an operating company millions of dollars depending on difficulty and risk, in extreme cases wellbore have been lost due to fishing operations and associated costs. 
         [0007]    Accordingly, there is a need in the art for a well completion process and plug which will allow the plug to behave like a frac plug for a temporary period of time and then allow the flow of gas and or oil from the reservoir up to the well head without the need for drilling the plug out. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention relates generally to a process and apparatus for multiple interval isolation of a horizontal or vertical well, where intervention such as drilling out frac plugs is not necessary for well completions. Generally, pumpable seat assembly is provided, which is a seat and slip assembly that would be applicable to more than 80% of vertical and horizontal completions activity within the industry and that can be configured to fit all casing sizes and casing weights. In one embodiment, the pumpable seat assembly would be deployed or pumped on electric wireline down the well by itself or in combination with the perforating guns to a desired depth within the well. A standard setting tool would set the pumpable seat assembly in the casing and the wireline would then log on depth the guns and perforate the interval at desired depth and pull to surface. 
         [0009]    In one aspect, a dissolvable member is provided. In one embodiment, the dissolvable member is a dissolvable ball which would be dropped by the service provider into the well from surface and then pumped downhole until the dissolvable ball lands on the pumpable seat assembly and provides isolation from the previous interval for frac stimulation purposes. The process can then be repeated a multiple number of times in the same wellbore using additional pumpable seat assemblies and dissolvable balls. Once the frac or stimulation services are completed, the dissolvable ball will dissolve and the well can be flowed on production, or equipped with production tubing, all without any wellbore intervention. It is understood that the term “dissolvable ball” includes any degradable or biodegradable ball. 
         [0010]    In another embodiment, the dissolvable member is a dissolvable valve (e.g., dissolvable poppet valve or dissolvable flapper/check valve) or a solid dissolvable plug, which is installed in the pumpable seat assembly and therefore the dissolvable member would be would be deployed or pumped downhole together with the pumpable valve assembly. 
         [0011]    In another aspect, a pumpable seat assembly is provided having a non-dissolvable isolation device such as a non-dissolvable poppet valve or non-dissolvable flapper. 
         [0012]    In one aspect, the pumpable seat assembly has an inner diameter that is equal to or greater than about 1 inch. In one embodiment, the assembly has an inner diameter of about 2 inches or larger. In another embodiment, the pumpable seat assembly has an inner diameter that is between about 1 inch to about 2 inches in diameter. By having a larger inner diameter than conventional frac plugs, once the dissolvable member has dissolved, the flow would not be restricted. 
         [0013]    In one aspect, the invention comprises a process for fracturing, stimulating and producing a wellbore having a plurality of oil or gas producing zones, comprising: 
         [0014]    introducing into the well a pumpable seat assembly comprising a generally cylindrical tube having an outer diameter and an inner diameter with an upper end forming a ball seat; 
         [0015]    setting the pumpable seat assembly below an oil or gas producing zone to be produced; 
         [0016]    introducing a dissolvable ball into the well, said dissolvable ball having a sufficiently large enough outer circumference so that it can sit on the ball seat and temporarily restrict a flow of fluids to the portion of the wellbore located below the pumpable seat assembly; 
         [0017]    fracturing the oil and gas producing zone to stimulate oil or gas production; whereby the dissolvable ball is configured to dissolve within a predetermined period of time so that when it dissolves any oil or gas produced from zones below the pumpable seat assembly can flow through the cylindrical tube. 
         [0018]    In one embodiment, the inner diameter of the cylindrical tube is sufficient to allow relatively unrestricted flow of oil or gas there through. In one embodiment, the inner diameter is equal to or greater than about 1 inch. In one embodiment, the inner diameter is about 2 inches or larger. In another embodiment, the pumpable seat assembly has an inner diameter that is between about 1 inch to about 2 inches in diameter. 
         [0019]    In another aspect, the pumpable seat assembly is provided for temporarily sealing a well casing, the pumpable seat assembly comprising: 
         [0020]    a generally cylindrical tube having an outer diameter and an inner diameter with an upper end forming a ball seat; 
         [0021]    a upper slip assembly and a lower slip assembly mounted on such cylindrical tube and adapted to selectively engage the well casing to anchor the pumpable seat assembly; 
         [0022]    an elastomeric packing element mounted on said cylindrical tube between the upper slip assembly and the lower slip assembly; and 
         [0023]    a dissolvable ball having a sufficiently large enough outer circumference so that it can sit on the ball seat and temporarily restrict a flow of fluids to the portion of the wellbore located below the pumpable seat assembly. 
         [0024]    In one embodiment, the inner diameter of the cylindrical tube is equal to or greater than 1 inch. In another embodiment, the pumpable seat assembly has an inner diameter that is between about 1 inch to about 2 inches in diameter. In another embodiment, the pumpable seat assembly has an inner diameter that is about 2 inches in diameter or larger. In one embodiment, the cylindrical tube has at least one flow port located at a lower end of the cylindrical tube. 
         [0025]    In another aspect, the pumpable seat assembly is provided for temporarily sealing a well casing, the pumpable seat assembly comprising: 
         [0026]    a generally cylindrical tube having an outer diameter and an inner diameter; 
         [0027]    a upper slip assembly and a lower slip assembly mounted on such cylindrical tube and adapted to selectively engage the well casing to anchor the pumpable seat assembly; 
         [0028]    an elastomeric packing element mounted on said cylindrical tube between the upper slip assembly and the lower slip assembly; and 
         [0029]    a dissolvable member positioned within the generally cylindrical tube for temporarily restricting a flow of fluids to the portion of the wellbore located below the pumpable seat assembly. 
         [0030]    In one embodiment, the inner diameter of the cylindrical tube is equal to or greater than 1 inch. In one embodiment, the inner diameter is about 2 inches or larger. In another embodiment, the pumpable seat assembly has an inner diameter that is between about 1 inch to about 2 inches in diameter. In one embodiment, the cylindrical tube has at least one flow port located at a lower end of the cylindrical tube. In one embodiment, the dissolvable member is selected from the group consisting of a dissolvable poppet valve, a dissolvable flapper/check valve and a solid dissolvable plug. 
         [0031]    In one embodiment, the dissolvable member comprises a polymer that is dissolvable by water, pH, enzymes and the like. 
         [0032]    Additional aspects and advantages of the present invention will be apparent in view of the description, which follows. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings: 
           [0034]      FIG. 1  is a cross-sectional view of an exemplary embodiment of the pumpable seat assembly having a dissolvable ball. 
           [0035]      FIG. 2  is a partial cross-sectional perspective of a plurality of pumpable seat assemblies as shown in  FIG. 1  set within a length of well casings. 
           [0036]      FIG. 3  is a cross-sectional view of an exemplary embodiment of the pumpable seat assembly having a dissolvable plug or valve member. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0037]    The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practised without these specific details. 
         [0038]    The present invention relates generally to a process for fracturing, stimulating and producing a wellbore without having to mill out and remove fracturing/bridge plugs and to a pumpable seat assembly for use therein. 
         [0039]      FIG. 1  shows one embodiment of a pumpable seat assembly ( 10 ) useful in the present invention, which assembly ( 10 ) is shown being set within a wellbore casing ( 12 ). Pumpable seat assembly ( 10 ) comprises a generally cylindrical tube ( 14 ) having an upper end ( 15 ) and a lower end ( 17 ). Situated near the first end ( 15 ) of cylindrical tube ( 14 ) is an upper slip assembly ( 18 ) and situated near the lower end ( 17 ) of cylindrical tube ( 14 ) is a lower slip assembly ( 22 ). Both the upper and lower slip assemblies generally include a plurality of serrations ( 23 ) which engage the casing ( 12 ) and prevent longitudinal movement of the slips ( 18 ) and ( 22 ) once set. 
         [0040]    An elastomeric packer element ( 20 ) is mounted on the cylindrical tube ( 14 ) between the upper slip (( 18 ) and the lower slip ( 22 ). The packing element ( 20 ) is adapted to be deformed into sealing engagement with the casing ( 12 ) upon compression of setting components (not shown). Although the packing element ( 20 ) is shown and described as being one-piece it is to be understood that a packing element having multiple members is contemplated under the present invention. In either case, the packing element ( 20 ) is adapted to provide a fluid-tight seal between the cylindrical tube ( 14 ) and the casing ( 12 ). 
         [0041]    The lower end ( 17 ) of the cylindrical tube ( 14 ) can further comprise one or more flow ports ( 24 ). The flow ports ( 24 ) facilitate the flow of oil or gas from the region below the pumpable seat assembly ( 10 ) through the cylindrical tube ( 14 ) to the wellhead (not shown). The upper end ( 15 ) further comprises a time-dissolvable ball ( 28 ), which ball ( 28 ) is sized to generally sit into and cover the seat ( 16 ) formed in the upper portion ( 15 ) of the cylindrical tube ( 14 ) to prevent the flow of fluids such as those used for fracturing, stimulating and the like from flowing through the cylindrical tube ( 14 ) to the formation below the pumpable seat assembly ( 10 ). The ball ( 28 ), however, is dissolvable within a predetermined passage of time to then allow the flow of oil and gas from the formation below to the surface. Thus, the dissolvable ball ( 28 ) functions to temporarily restrict the flow through the cylindrical tube ( 14 ) until it is desirable to do so. The inner diameter (ID) of the cylindrical tube must be large enough so that unrestricted flow can occur therethrough. In one embodiment, the ID is about  2  inches or larger. This is due to the varying casing sizes that the tools are run in. 
         [0042]    An example of biodegradable balls that may be used in the present invention is BioBalls™, which are soluble ball sealers that are completely soluble in all aqueous fluids such as fresh water, brine and acid. The solubility rate is time and temperature dependent and works in static or agitation fluids. BioBalls™ are available from Santrol. It is understood that there are many service providers that can supply dissolvable products. Generally, dissolvable balls can include biodegradable balls that can degrade over a period of hours or days when exposed to a set of predetermined environmental conditions. For example, the environmental conditions can include normal wellbore operating conditions of temperature and pressure at a particular depth or elevation in the wellbore, as well as the normal chemistry for drilling mud or pumping/frac fluids used during completion operations. 
         [0043]      FIG. 2  shows an embodiment of a well completion process of the present invention using a plurality of pumpable seat assemblies ( 10 ) of the present invention. In FIG.  2 , a horizontal portion of a well is shown which has been cased in with casing ( 12 ), such as steel pipe casing. The casing ( 12 ) may be cemented in place in the well. The horizontal well portion in  FIG. 2  comprises five separate producing zones, zone A, zone B, zone C, zone D and zone E. The end of the casing ( 12 ) is shown as element ( 130 ). The first zone to be fractured/stimulated would be the zone closest to the casing end ( 130 ), namely, zone A. A perforating apparatus (not shown) can be used to form perforations  132  in the casing ( 12 ) and fracing/stimulating fluids can then be pumped down to complete the fracing/stimulating process. 
         [0044]    The next producing zone to be perforated/fractured/stimulated would now be zone B. However, it is desirable that any fracing/stimulating fluids that are used to stimulate zone B do not reach zone A to prevent re-stimulating or re-fracturing of an already stimulated/fractured zone/interval. Thus, pumpable seat assembly ( 10   a ) is pumped downhole and set just below zone B but above zone A. Dissolvable ball ( 28   a ) is then pumped down to cover the open seat of pumpable seat assembly ( 10   a ). This will then prevent any fracing/stimulating fluid from reaching zone A. After zone B is stimulated, the next zone to be perforated/fractured/stimulated is zone C, using a second pumpable seat assembly ( 10   b ) which is pumped down the wellbore casing ( 12 ) followed by a second dissolvable ball ( 28   b ). After zone C is stimulated, zone D is the next producing zone to be perforated/fractured/stimulated using pumpable seat assembly ( 10   c ) and dissolvable ball ( 10   c ). Finally, pumpable seat assembly ( 10   d ) and dissolvable ball ( 10   d ) is used when zone E is perforated/fractured/stimulated. 
         [0045]      FIG. 3  shows another embodiment of a pumpable seat assembly ( 310 ) useful in the present invention, which assembly ( 310 ) is shown being set within a wellbore casing ( 312 ). Pumpable seat assembly ( 310 ) comprises a generally cylindrical tube ( 314 ) having an upper end ( 315 ) and a lower end ( 317 ). Situated near the first end ( 315 ) of cylindrical tube ( 314 ) is an upper slip assembly ( 318 ) and situated near the lower end ( 317 ) of cylindrical tube ( 314 ) is a lower slip assembly ( 322 ). Both the upper and lower slip assemblies generally include a plurality of serrations ( 323 ) which engage the casing ( 312 ) and prevent longitudinal movement of the slips ( 318 ) and ( 322 ) once set. 
         [0046]    An elastomeric packer element ( 320 ) is mounted on the cylindrical tube ( 314 ) between the upper slip ( 318 ) and the lower slip ( 322 ). The packing element ( 320 ) is adapted to be deformed into sealing engagement with the casing ( 312 ) upon compression of setting components (not shown). Although the packing element ( 320 ) is shown and described as being one-piece it is to be understood that a packing element having multiple members is contemplated under the present invention. In either case, the packing element ( 320 ) is adapted to provide a fluid-tight seal between the cylindrical tube ( 314 ) and the casing ( 312 ). 
         [0047]    The lower end ( 317 ) of the cylindrical tube ( 314 ) can further comprise one or more flow ports ( 324 ). The flow ports ( 324 ) facilitate the flow of oil or gas from the region below the pumpable seat assembly ( 310 ) through the cylindrical tube ( 314 ) to the wellhead (not shown). The upper end ( 315 ) further comprises a dissolvable member ( 346 ), such as a dissolvable valve or plug, which prevents the flow of fluids such as those used for fracturing, stimulating and the like from flowing through the cylindrical tube ( 314 ) to the formation below the pumpable seat assembly ( 310 ). The dissolvable member ( 346 ), however, is dissolvable within a predetermined passage of time to then allow the flow of oil and gas from the formation below to the surface. Thus, the dissolvable member ( 346 ) functions to temporarily restrict the flow through the cylindrical tube ( 314 ) until it is desirable to do so. The inner diameter (ID) of the cylindrical tube must be large enough so that unrestricted flow can occur therethrough. In one embodiment, the ID is about 2 inches or larger, due to the varying casing sizes that the tools are run in. 
         [0048]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.