Abstract:
An array of plugging devices are pumped sequentially from the surface through a liner that typically becomes horizontal in nature, where each plugging device is anchorable at a specific position along the length of the line. Perforations are generated above the plugging device. The plugging device may be a cup plug and when pump pressure is applied to the cup the cup moves through the liner. When anchored, the cup directs frac fluids through the perforations to treat the well formation. The plug may be of the type where a full bore is maintained through the liner and allows the cup plug to travel back to the surface due to flow from the well thus eliminating any need for milling obstructions from the well bore. The use of multiple plugging devices allows multizone stage fracing.

Description:
This application claims priority to Provisional Application Serial No. 61/613,540 filed on Mar. 21, 2012. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to apparatus and methods for oil and gas wells to enhance the production of subterranean wells, either open hole, cased hole, or cemented in place and more particularly to improved multizone stimulation systems. 
     2. Description of Related Art 
     Wells are drilled to a depth in order to intersect a series of formations or zones in order to produce hydrocarbons from beneath the earth. Some wells are drilled horizontally through a formation and it is desired to section the wellbore in order to achieve a better stimulation along the length of the horizontal wellbore. The drilled wells are cased and cemented to a planned depth or a portion of the well is left open hole. 
     Producing formations intersect with the well bore in order to create a flow path to the surface. Stimulation processes, such as fracing or acidizing are used to increase the flow of hydrocarbons through the formations. The formations may have reduced permeability due to mud and drilling damage or other formation characteristics. In order to increase the flow of hydrocarbons through the formations, it is desirable to treat the formations to increase flow area and permeability. This is done most effectively by setting either open-hole packers or cased-hole packers at intervals along the length of the wellbore or cementing in the horizontal liner. When using packers the packers isolate sections of the formations so that each section can be better treated for productivity. Between the packers is a frac port and in some cases a sliding sleeve or a casing that communicates with the formation. In order to direct a treatment fluid through a frac port and into the formation, a seat or valve may be placed close to a sliding sleeve or below a frac port. A ball may be dropped to land on the seat in order to direct fluid through the frac port and into the formation. 
     One method, furnished by PackersPlus, places a series of ball seats below the frac ports covered by sliding sleeves with each seat size accepting a different ball size. Smaller diameter seats are at the bottom of the completion and the seat size increases for each zone as you go up the well. For each seat size there is a ball size so the smallest ball is dropped first to clear all the larger seats until it reaches the appropriate seat. In cases where many zones are being treated, maybe as many as 20 zones or more, the seat diameters have to be very close. The balls that are dropped have less surface area to land on as the number of zones increase. With less seat surface to land on, the amount of pressure you can put on the ball, especially at elevated temperature, becomes less and less. This means you can&#39;t get adequate pressure to frac the zone because the ball is so weak, so the ball blows through the seat. Furthermore, the small ball seats reduce the I.D. of the production flow path which creates other problems. The small I.D. prevents re-entry of other downhole devices, i.e., plugs, running and pulling tools, shifting tools for sliding sleeves, perforating gun size (smaller guns, less penetration), and of course production rates. In order to remove the seats, a milling run is needed to mill out all the seats and any balls that remain in the well. 
     The size of the ball seats and related balls limits the number of zones that can be treated in a single trip. 
     It would be advantageous to have a system that had no ball seats that restrict the I.D. of the tubing and to eliminate the need to spend the time and expense of milling out the ball seats, not to mention the debris created by the milling operation. Also, it would be advantages to eliminate the restricted flow paths due to the small I.D. of the ball seats that could potential restrict production. 
     Another method of completion is called “Plug and Perf”. In these completions the liner may be cemented in throughout the length of the horizontal section. Typically, composite plugs are run into the well on electric line and pumped out the horizontal section toward the toe until the composite plug is below the section of the zone to be fraced. Once at the desired location, a setting tool is actuated and the composite plug sets inside of the liner. Perforating guns are sometimes run in the same electric line trip where once the composite plug is set, the guns and setting tool release away from the composite plug and are moved up to a location where the liner is perforated with the guns. Once perforated, the spent perforating gun and setting tool are returned to the surface. Frac fluid is then pumped into the well in order to frac the zone. After treatment, the next composite plug with setting tool and perforating guns is run to the next upper zone section and the process described above is repeated and obviously this becomes very time consuming. This process can be repeated many times and in some cases up to 40 times. Once all zones have been fraced, a coiled tubing unit runs coiled tubing into the well with a motor and mill attached and all of the composite plugs are milled out. The composite plug mill debris is flowed back to the surface and the well is put on production. 
     It would be advantageous, and cost effective, to have a system and method where no wireline trucks were required to perform electric line runs to run and set composite plugs, perforate, and return tools to the surface. Furthermore, it would be advantageous and cost effective, to eliminate the need to call a coiled tubing unit to location to mill out the composite plugs. 
     The “Plug and Perf” method is sometimes desired over the sliding sleeve method because last minute changes can be made on zone spacing since the composite plugs can be set at any location along the length of the well. The present invention offers a solution to making position changes of the plug in the liner at the last minute by use of selective key profiles located at each liner coupling. Casing liner comes in length increments ranging from 30 to 40 feet and typical stage zone lengths vary maybe from 300 feet to 500 feet. So, for example, a 300 foot zone may have about 9 selective profiles to choose from when anchoring or positioning a cup plug. Therefore, a plug key profile can be selected at the surface to match a liner coupling profile where the plug is desired to land and anchor in place. The plug key profile can be designed to pass certain liner coupling profiles until the plug finds the correct profile. The plug key profile is also designed to easily disengage from the from the liner coupling profile so that flow from the well will return the plug back to the surface thus eliminating the need to mill out the plug. 
     The “Plug and Perf” method can also use a conventional wireline conveyed perforating gun attached to the top of the cup plug. In this case the cup plug serves a dual purpose, i.e., first, conveys the tools to a location, and second, provides a seal to frac against. It would be advantageous to use the cup plug as a power means to pump the perforating guns out the horizontal wellbore and land the cup plug in a profile to positively locate the guns along the horizontal section. The perforating guns could be detached from the cup plug by different means, i.e., apply pump pressure to the cup and jar up on the guns to release from the plug or incorporate an electrical triggered release device between the guns and the cup plug. Once the perforating gun is released from the cup plug, the gun is positioned at selected locations above the plug. A single shot gun can be used or a select fire can be used to generate a series of perforation clusters within a zone. 
     The invention is not to be limited to wireline, or electric line, conveyed guns attached to the cup plug since a pressure actuated type gun can be attached to the top of the cup plug providing safety issues can be resolved in cases where the guns do not fire and have to return to the surface for disarmament. This would be advantageous since a wireline trip would be eliminated. 
     SUMMARY OF THE INVENTION 
     This invention provides an improved completion system for wells where stage fracing is desired for horizontal wells. The invention includes advantages over current systems in order to reduce completion costs and increase production rates. A series of plugs are landed in various full bore profiles where specific profiles are located at pre-selected positions along the length of the horizontal wellbore. The use of a cup on the plug eliminates the need to run an electric line setting tool to set the plug, therefore, the plug can be pumped out a horizontal wellbore once a circulation path is created at the toe of the well. A similar cup plug is described in U.S. provisional patent application Ser. No. 12/925,141 but has been modified and its use expanded per the present invention. The plug does not have to be stroked to a set position, from a run-in position with a setting tool, since the cup on the plug forms a seal with the inside of the liner and directs frac fluid into the formation. A first plug is pumped to a position closest to the toe of the wellbore, the plug engages a profile in the inside diameter of the sleeve that does not let the plug pass. The sleeve then, with the plug located and sealing inside the sleeve, shifts to open a series of frac ports. The first zone is fraced thru the frac ports and then at the right time while pumping, a second plug is released from the surface and pumped out the horizontal section to land in a second pre-selected location in the wellbore. This process is repeated for all zones to be fraced. Once fracing is completed then production begins thereby flowing all the plugs back to surface for retrieval, thus eliminating the need to mill out the plugs. All the profiles used can be varied from zone to zone so that each plug only lands in a certain location. Selection of a plug profile at the surface, even though receiving profiles are already in the well, allows selective plug placement along the horizontal section. The profiles are designed to stop the plugs from going down but allow the plugs to go back up the well to the surface. The full bore profiles also eliminate ball seats that can limit production flow due to flow restrictions. The cup plugs can also be used to pump perforating guns along the wellbore and positively locate the guns before creating perforations in the liner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of the present invention where the cup plug has landed in a liner collar profile. This condition exists when it is desired to position a plug and then perforate above the plug. 
         FIG. 2  is a schematic of two different profiles, but only two of many possibilities, illustrating how the profiles can be selective. 
         FIG. 3  is a schematic of a wireline conveyed perforating gun attached to a cup plug where the cup plug is used to conveyed the assembly out the wellbore and latch into a profile to locate both the plug and the guns relative to the length of the horizontal section of the wellbore. 
         FIG. 4  is a schematic of the present invention where the cup plug has landed in a profile that is located in a sliding sleeve. This condition exists when it is not desired to perforate above the plug but instead break down the formation by applying frac pressure. 
         FIG. 5  is a schematic of the present invention where the cup plug has landed in a profile that is located in a sliding sleeve and applied pump pressure has acted on the cup to create a force to shift the sleeve down to uncover a series of frac ports. 
         FIG. 6  is a schematic of the present invention that shows two cup plugs, with wireline perforating guns attached, pumped into the horizontal section landed in collar profiles. 
         FIG. 7  is a schematic of the present invention that shows two cup plugs and sliding sleeves in a horizontal wellbore. Only two are shown but many can be used. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , the cup plug  36  is positioned inside of liner  1  which connects with liner collar  2  at thread  11 , and liner  3  connects to liner collar at thread  18 . Top sub  4  has standard wireline threaded connection  5  and fish neck  6 , that are optional, and finned centralizer  7 . Hollow pocket  72  communicates with holes  71  where holes exit under cup  9 . Top sub  4  threadably connects at thread  8  to mandrel  19 . Hole  68  connects to ball seat  69  where ball  70  is housed. Sealing cup  9  and thimble  10  slide over mandrel  19  over surface  13 . Seal  12  seals on surface  13  and cup surface  27  seals at liner surface  26 . Cup  9  prevents fluid  30  from traveling to location  34 . Thimble  10  has surface  28  that shoulders against mandrel surface  29 . A radial series of profile keys  15  are retained to mandrel  19  by retainer rings  14 . Key profile  21  expands and matches profile  20  that is located in liner coupling  2 . Springs  16  acts on surface  17  and against the inside surfaces of a series of keys  15  to bias the keys outward into profile  20 . Surfaces  26 ,  35 , and  26  are nearly the same as to maintain a full bore through the casing or liner. Key shoulders  24  engage against collar shoulder  25  to prevent cup plug  36  from moving downward. Key surfaces  23  is such that they slide on surface  22  of the collar to allow plug  36  to cam keys  15  inward to allow plug  36  to move upward toward the surface. Shoulder  32  of cup  9  engage shoulder  33  of top sub  4  so cup  9  is trapped between top sub  4  and mandrel  19 . In lieu of a cup shaped member for the seal, other types of seals such as a Labyrinth type seal could be used as a substitute for sealing cup  9 . 
     With reference to  FIG. 2 , liner coupling  2  has inner profile  20  and key  15  has outer profile  21 . Dimensions A 1  and A 2  represent lengths of a first set of keys  15  and coupling  2 . Dimension B 1  represent a second profile  21  for a liner coupling  2 . The “A 2 ” dimension of key  15  is longer than the “B 1 ” dimension for liner coupling  2  so the “A 2 ” profile will not engage in liner coupling profile “B 1 ” but will engage in coupling profile “A 1 ”. The longer liner coupling  2  dimension “A 1 ” is positioned in the horizontal liner below, or closer to the toe of the horizontal well, than the shorter liner coupling dimension “B 1 ” so the cup plug  36  will pass through liner collar “B 1 ” and stop in liner collar “A 1 ”. Profiles  20  and  21  are varied into many combinations in order to increase the number of profile combinations and to allow selective positioning of multiple cup plugs in multiple liner collars. 
       FIG. 3  shows a cross-sectional view of the cup plug  36  attached to a perforating gun  37  at thread  5  and shoulder  38 . The cup plug  36  has landed in collar  2  in profile  21  with selective key profile  20 . Cup  9  is sealing inside of liner  1 . Liner  1  has holes  40  generated from shaped charges  39  and jets  41  from perforating gun  37 . Electric line  67  is attached to perforating gun  37  to allow electrical detonation of the guns by the way of firing mechanism  42 . Firing mechanism  42  may be of the type use on conventional wireline perforating guns with safety features built in the prevent firing out-of-zone. Also, firing mechanism  42  can be of the pressure actuated type with or without wireline in the hole with the appropriate safety features present. A release mechanism can be added at location  38  in order to detach the perforating guns  37  from plug  36  before or after the guns are detonated. 
       FIG. 4  shows a cross-section of the cup plug  36  inside of liner  1 , which is connected to liner collar  44  with thread  43 , and sliding sleeve  52 . Key profile  21  is landed into sliding sleeve profile  20  so cup plug  36  engages and locks into sliding sleeve  52 . Cup  9  seals inside of sliding sleeve  52 . Seals  45  and  48  seal in bores  49  and prevent fluid form passing through ports  46 . Shear screws  47  secure sliding sleeve  52  to collar  44  by engaging shoulders  51 . Shoulder  50  is positioned at the top of collar  44 . 
       FIG. 5  shows the sleeve  52  shifted downward so that shoulder  53  contacts shoulder  54 . Frac ports  46  are exposed to fluid  30  so that fluid  30  can pass through ports  46 . 
       FIG. 6  shows well liners  1  and collars  2  in formation  63 . At the toe end of the well is circulation valve  57  that consists of differential piston  60 , seals  58  and  62  on the piston  60 , port  59 , and housing  61 . The cup pug  36  and perforating gun  37  are connected and are positioned at two separate zones in the well liner  1 . The perforating guns  37  are shown making perforations  41  to communicate with zones  63 . Wireline  67  is shown connected to perforating gun  37  and going to surface  64 . 
       FIG. 7  shows the cup plugs  36  positioned in two sliding sleeves  52  that are connected to liners  1 . Liners  1  and sliding sleeves  52  are cemented  56  into zone  63 . Fractures  65  are shown propagating from the sliding sleeve ports into formation  63 . Lubricator  66  is shown positioned at the surface  64  to catch the cup plugs when production begins. Circulation valve  57  is shown at the toe of the well. The circulation valve can be replaced with any device or method that allows circulation to the toe of the wellbore. 
     DESCRIPTION OF OPERATION 
     Referring to  FIG. 1 , cup plug  36  is pumped through the well liner  1  by applying fluid pressure  30  to cup  9 . The area created by cup surface  27  sealing on liner surface  26  times the applied pump pressure creates a force to move cup plug out the horizontal wellbore. Thimble  10  acts as a backup to cup  9  so the cup  9  can withstand high frac pressures applied during fracing. The o-ring  12  prevents fluid from passing under the cup  9 . Finned centralizer  7  keeps cup  9  centered in liner  1  for improved sealing. Keys  15  are expandable and retractable and are biased outward with spring force from spring  16 . When key profile  21  enters collar profile  20  the keys expand and snap into the profile and shoulders  24  and  25  engage so that the cup plug  36  cannot go down past the collar profile. The engagement between shoulders  24  and  25  is of sufficient strength as to prevent the cup plug  36  from moving down when frac pressure  30  is applied to the cup  9 . The top of the cup plug  36  has thread  5  to allow attachment of wireline tools and has a fish neck if retrieval operations are ever needed. After fracing the zones in the well the cup plug is flowed back to the surface by flow due to production. The keys  15  have gradual profiles  23  that contact gradual collar profiles  22  so that little force is needed to retract keys  15  so that the cup plug  36  can move upward. Hole  68 , pocket  72 , and holes  71  are present so that production fluids will clean any proppant settlement out from under cup  9  that might prevent the plug from moving upward. The flow area through hole  68  is small so that a differential will remain higher below the cup plug so that the plug will move upward. The ball  70  seals on seat  69  to prevent the passage of frac fluid or pumping fluid. The key profiles and collar profiles are placed throughout the length of the horizontal wellbore typically with longer profile near the toe of the well and shorter profile near the surface of the well. The longer profiles will pass the shorter profiles until the matching profile is reached by the cup plug and the cup plug will latch in and stop. 
     Referring to  FIG. 3 , the perforating gun  37  is attached to the cup plug  36  and a wireline is attached to the perforating gun, see  FIG. 6 . The cup plug  36  is pumped down to a liner collar that has a matching profile to the cup plug. The cup  9  seals inside of liner  1  to prevent frac fluids from passing the cup plug. Perforating gun  37  can be detached, if desired, and moved to a location where it is desired to perforate liner  1 . The perforating gun is removed from the well and the zone if fraced. This process is repeated for the planned number of zones to be fraced. After fracing the well production flows the cup plugs back to the surface which leaves a full bore through the liner and no need to mill out the plugs. 
     Referring to  FIGS. 4 and 5 , the cup plug  36  is used in this case when it is desired not to run perforating guns, but instead, open flow holes  46  to the formation by shifting a sliding sleeve  52 . Once the spring loaded key with profile  21  lands into sliding sleeve with profile  20 , and the cup plug locks into sliding sleeve  52 , pump pressure applied to cup  9  shifts the cup plug and sliding sleeve  52  downward, shearing shear screws  47  and allowing seal  45  to cross port  46  to allow fluid communication from inside the liner  1  to the outside of liner  1 . The cup  9  seals inside of the sliding sleeve so that frac fluid is directed into the well formation. As shown in  FIG. 7 , multiple cup plugs can be pumped into position, the zones fraced, and the plugs flow back to surface when production begins. In to above described operation, no wireline runs are required and no coiled tubing milling operations are needed. Also it is possible to omit the sealing cup so that the mandrel and the expanding keys are sufficient to divert fracturing fluid to a point above the plug into the formation. 
     Those familiar with the art of completing wells realize that other advantages might exist with the present invention, such as making the cup plug out of composite materials or adding a means to prevent the cup plug from rotating should the occasion arise where the cup plug would have to be milled out. Also, for example, the cup plug could be run with other types of completion systems as desired.