Patent Application
20110198096
1. Field of the Invention
This invention pertains to a system for injecting treatment fluids into a selected isolated interval in an oil and gas well. More particularly, valves disposed along a tubular are opened sequentially by pumping balls of one size down the tubular, causing one valve to open and another valve mechanism to be moved into position to be opened by a following ball.
2. Description of Related Art
Treatment fluids, such as hydraulic fracturing or acidizing fluids, are often used to treat multiple zones or segments of the earth penetrated by a wellbore. It is usually preferable to treat each zone or segment individually and to divert the treating fluid to another zone or segment when a designed amount of treating fluid has been injected into a zone or segment. In vertical wells, different zones of a producing formation are normally treated individually. In the horizontal wellbore portion of “horizontal wells,” different segments of the horizontal wellbore are often treated individually. This treatment may be a hydraulic fracturing treatment. It is common to isolate segments of horizontal wellbores by packers, either on casing in open hole or on tubing in a cased and perforated well. Packers are provided to isolate the zone to be treated so that fluid under pressure will be directed outwardly of the well and confined within a given zone or segment. In a horizontal well in shale gas reservoirs, it has become common to isolate the horizontal wellbore into ten or more segments and fracture each segment independently. The goal is to create multiple hydraulic fractures transverse to the wellbore, which are critical to producing gas from the well at economic rates.
A common method for opening valves disposed along a casing or tubing in a well is the use of sliding sleeves, which may be opened by a tool run into the well. Another method is to place a ball in the injected fluid at a time when it will seat on a receiving apparatus connected to a sliding sleeve when it is desired to open the sliding sleeve. Fluid pressure behind the ball opens the sleeve or valve. To open a plurality of valves, it is necessary to use different size balls, starting with the smallest ball to seat on the lowest sleeve apparatus, which will pass through the larger seats. Balls of increasing size are injected to divert fluid to another zone or segment. The use of such apparatus and method is described in the article “Considered approach improves hydraulic fracturing in horizontal open holes,” E&P Magazine, Jul. 1, 2009. This article discusses some of the limitations of the present method. The use of sequentially smaller ball seats on sleeves within the well results in a limited number of unique seats for a given tubing size and in a limited number of unique zones for a fracture project. Drastically reduced internal seat diameters are required as the distance from the well head to the fracturing zone increases. This results in reduced production from the lower zones and frequently requires post-fracturing drilling operations to remove the seats.
This approach is also described in U.S. Pat. No. 7,387,165. This requires a complicated ball launching system for balls of varying diameter and opens up the possibility of mis-ordering the balls, which would then unintentionally block off a given zone.
What is needed is apparatus and method for diverting treating fluids in a wellbore that does not require balls of varying size, such that any selected number of zones or intervals in a well can be treated.
The invention as disclosed includes a well treating system that may include a lower initiation tool and a plurality of intermediate diverter valves that are positioned in zones or segments that are isolated by packers. Each diverter valve includes a sliding valve member that is axially moved as a result of a spherical ball being captured by a collet within the valve. All the balls are of the same diameter. Opening of the lowermost valve results in the next uphole valve being placed in a set position so that after the fracturing process is completed in the adjacent downhole fracturing zone, the valve is ready to be actuated by directing a subsequent ball down the well bore.
The invention overcomes many of the above noted deficiencies with the prior art. A single size ball is employed which allows for a larger diameter production tube to be employed. This increases production compared to the prior art which requires sequentially smaller diameter balls and tubing. Since all the balls are of the same size, the possibility of mis-ordering the balls is eliminated and consequently accidental isolation of fracturing zones is eliminated, as is the requirement for post-fracturing drilling operations to remove the ball seats. Also, since the balls are of a uniform size and there is no need to reduce the diameter of the ball seats, an unlimited number of fracturing zones or intervals can be isolated and treated for a given well.
The drawings provided herein are meant to illustrate the principles of the invention in general terms and are not intended to limit the invention to the specific details shown the drawings. Other shapes and sizes for the various structural members could be used without departing from the invention, which is set forth in the accompanying claims. Also the drawings are not necessarily drawn to scale. The drawings depict the invention in a vertical direction, but it should be understood that the apparatus can be used in vertical or horizontal wells or wells at any angle.
Referring to
To begin the fracturing process for the first fracturing zone a ball is initially placed or dropped down through tubing 2 and rests upon ball seat 10. The fracturing fluid under pressure will exert a downward force on the ball and cause valve sleeve 7 to move axially after shearing the pins 11. As shown in
Details of a diverter valve 35 will now be discussed with reference to
A collet 43 is located within the valve housing 40 and is axially movable within the housing. At its lower end the collet is provided with a plurality of collet fingers 44. A hydraulic logic piston 46 is attached to an intermediate portion of collet 43 by a plurality of shear pins 49. An annular chamber 45 is formed between the logic piston 46 and an interior wall portion of the valve housing 40. A passageway 92 communicates with jumper conduit 16 and chamber 45. The upper surface area 93 of hydraulic logic piston 46 is greater than that of its lower portion 94 so that fluid pressure within the diverter valve urges the logic piston 46 and consequently the collet in a downward direction as viewed in
The upper portion of a diverter valve 35 is shown in
As mentioned above, when the lower initiation tool is in the open position shown in
When the fracturing process is completed in the first fracturing zone, another ball 30 is introduced into the tubing. The ball is captured by the flexible fingers 44 of the collet which is in the set position as shown in
When the fracturing process is completed, flow of the fracturing fluid is stopped and the pressure acting on the balls is eliminated. At this point all of the balls can be flowed back out of the well. All of the collets are returned to their original position by springs 48 and full flow through the tubular can now occur. The diverter valves are now in the reset made as shown in
The operation of the fracturing system is as follows. The lower initiation tool and all of the diverter valves are positioned in the well in a closed mode. The first ball is dropped down to the lower initiation tool, and comes to rest on shoulder 10. At this point the pressure of the fracturing fluid will cause valve sleeve 7 to shift downwardly bringing valve sleeve ports 8 into alignment with outlets 9. Shear pins 11 are severed and snap ring 13 moves into snap ring groove 14. Packers 3 isolate the fracturing zone so that fracturing fluid is confined under pressure within the fracturing zone. Movement of the valve sleeve 7 also opens up vent port 81 which relieves pressure within chamber 45 in the adjacent diverter valve so that hydraulic logic piston 46 in the diverter valve can move under pressure to its lower position which in turn moves collet 43. Collet fingers 44 are thereby compressed inwardly by surface 91 to the set position shown in
When fracturing of the first zone is completed, the next ball is launched and is captured by the compressed collet fingers in the diverter valve above the first zone. The fracturing fluid pressure now causes collet 43 to move to the open position in
This process can be continued indefinitely with the same size balls. Once all fracturing operations are complete, all of the balls can be flowed back out of the well. When fracturing fluid flow and pressure are removed, the collets in all of the diverter valves are returned to their original position by springs 48. They are now reset as shown in
Various modifications may be made without departing from the invention as disclosed. For example, the lower initiation tool may be replaced by a diverter valve with the collet pinned in the set position. Other modifications will be apparent to those with ordinary skill in the art.
