This disclosure relates to downhole tools for use in oil and gas wellbores and to methods for treating wellbores. This disclosure particularly relates to downhole packers that are convertible from a bridge plug to a frac plug without removing the packer from the wellbore.
In the drilling or reworking of oil wells, numerous varieties of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in a well casing when it is desired to pump cement or other slurry down the tubing and force the slurry out into a formation. Thus, it becomes necessary to seal the tubing with respect to the well casing, and to prevent the fluid pressure of the slurry from lifting the tubing out of the well. Downhole tools, referred to as packers and bridge plugs, are designed to provide for the ability to seal tubing or other pipe in the well casing, and are well known in the art of producing oil and gas.
Packers and bridge plugs typically make use of metallic or non-metallic slip elements, or slips. The slips are initially retained in close proximity to the mandrel, but are subsequently forced outwardly away from the mandrel to engage a casing that was previously installed within the wellbore. Thus, when the tool is positioned at the desired depth, the slips are forced outward against the wellbore to secure the packer, or bridge plug, so the tool will not move relative to the casing during operations. Some non-limiting example operations include testing, stimulating production of the well, or plugging all or a portion of the well.
One problem encountered by well operators using packers and bridge plugs is that the packer and/or plug must be removed prior to the installation of other types of plugs. A frac plug is a good example. A frac plug is essentially a downhole packer with a ball seat for receiving a sealing ball. When the packer is set and the sealing ball engages the ball seat, the casing, or other pipe in which the frac plug is set, is sealed. Once the sealing ball is set, the operator is able to pump fluid into the well, and pumped fluid may be forced into a formation above the frac plug. Often, it is necessary to completely block flow from a lower zone to facilitate treatment of an upper zone, or conduct some other process in the upper zone. After the initial treatment or other process is complete, it may be desirable to allow flow from the lower zone, and to be able to restrict that flow. There is a need for tools that can be set in the well to act as a bridge plug, and can be converted to a frac plug while in the well.
One disclosed embodiment is a downhole tool for use in a well. The downhole tool comprises a mandrel defining a central flow passage therethrough and a ball seat thereon. A sealing element is disposed about the mandrel. The downhole tool is movable from an unset to a set position in the well in which the sealing element engages the well. A solid plug for blocking flow through the downhole tool is removably connected in the mandrel. A sealing ball is positioned in the well and is longitudinally spaced from the ball seat. The application of a predetermined pressure in the well will simultaneously remove the solid plug and move the sealing ball into engagement with the ball seat.
Another embodiment provides a downhole tool for use in a well. The downhole tool comprises a mandrel having an upper and a lower end. The mandrel defines a longitudinal central flow passage therethrough. The mandrel also defines a ball seat on the upper end thereof. A sealing element is disposed about the mandrel for sealingly engaging the well. A plug is detachably retained within the mandrel and a rod is disposed within the longitudinal central flow passage. The rod has a first end contacting the plug, and a second end contacting a sealing ball to space the sealing ball from the ball seat.
Another embodiment provides a method for converting a downhole tool positioned in a well from a bridge plug to a frac plug. The method comprises lowering the downhole tool into the well. The downhole tool defines a longitudinal central flow passage therethrough. The method further includes the step of setting the downhole tool in the well, where the downhole tool engages the well. Flow through the tool is blocked in both an upward and a downward direction through the longitudinal central flow passage with a solid plug detachably connected to the tool. A sealing ball is positioned in the well above the longitudinal central flow passage. Pressure is increased in the well, thereby causing the solid plug to detach from the downhole tool and move the sealing ball into engagement with a ball seat that is positioned on the downhole tool. When the sealing ball is in engagement with the ball seat, downward flow through the downhole tool is prevented but upward flow therethrough is permitted.
In the description that follows, similar parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawings are not necessarily to scale, and the proportions of certain parts have been exaggerated to better illustrate details and features of the invention. In the following description, the terms “upper,” “upward,” “lower,” “below,” “downhole” and the like as used herein shall mean in relation to the bottom or furthest extent of the surrounding wellbore. This applies even though the well or portions of it may be deviated or horizontal. The terms “inwardly” and “outwardly” are directions toward and away from, respectively, the geometric center of a referenced object. Where components of relatively well-known designs are employed, their structure and operation will not be described in detail.
Referring to the drawings, and in particular
Referring to
Packer 24 is designed to be set in well 14. Thus, mandrel 26 has sealing element 36 disposed thereabout. A spacer ring 38 is secured to mandrel 26 with pins 40. Spacer ring 38 provides an abutment which serves to axially retain slip segments 42, which are positioned circumferentially about mandrel 26. Slip segments 42 may utilize ceramic buttons 44 as described in detail in U.S. Pat. No. 5,984,007, which is incorporated by reference herein. Slip retaining bands 46 serve to radially retain slip segments 42 in an initial circumferential position about mandrel 26. Slip retaining bands 46 may be made of a steel wire, a plastic material, or a composite material having the requisite characteristics of sufficient strength to hold the slip segments 42 in place prior to setting downhole tool 10, and are drillable. Preferably, slip retaining bands 46 are inexpensive and easily installed about slip segments 42. Slip wedge 48 is initially positioned in a slidable relationship to, and partially underneath, slip segment 42. Slip wedge 48 is shown pinned into place by pins 50. Located below the upper slip wedge 48 is at least one sealing element 36. The embodiment of
Located below a lower slip wedge 48 are a plurality of slip segments 42. A mule shoe 58 is secured to mandrel 26 by radially oriented pins and/or epoxy glue 60. Mule shoe 58 extends below the lower end 30 of mandrel 26 and has a lower end 62, which comprises lower end 13 of downhole tool 10. The lowermost portion of downhole tool 10 need not be a mule shoe 58, but could be any type of section, which serves to terminate the structure of downhole tool 10, or serves as a connector for connecting downhole tool 10 with other tools, a valve, tubing or other downhole equipment.
Referring back to
A rod 84 having upper end 86 and lower end 88 is disposed in longitudinal central flow passage 32. Lower end 88 engages solid plug 74, and is received in receptacle 78, making contact therewith. Upper end 86 extends beyond lower end 33 of ball seat 34 to space ball seat 34 from sealing ball 35 and to prevent sealing ball 35 from prematurely seating in ball seat 34. In an alternative embodiment, receptacle 78 is not utilized, and rod 84 simply contacts upper end 80 of plug 74.
The operation of downhole tool 10 is as follows. Downhole tool 10 is lowered into wellbore 12 with setting tool 22, which is a setting tool of a type known in the art. As downhole tool 10 is lowered into wellbore 12, flow through longitudinal central flow passageway 32 will be prevented due to solid plug 74. Sealing ball 35 is positioned and spaced from ball seat 34 by rod 84. Once downhole tool 10 has been lowered to a desired position in well 14, setting tool 22 is utilized to move downhole tool 10 from its unset position to the set position, as depicted in
To convert downhole tool 10, plug 74 is removed from mandrel 26. Removing plug 74 requires the exertion of a predetermined pressure to create a sufficient force upon plug 74 to detach or remove plug 74. In one embodiment, plug 74 is retained with shear pin 76 and the predetermined pressure force will shear pin 76. The fluid pressure required to remove plug 74 will be less than the pressure used to fracture a zone thereabove, so that tool 10 automatically converts to a frac plug upon the fracturing of a zone thereabove. The shearing of shear pin 76 allows plug 74 and rod 84 to fall through well 14. Upon the detaching of plug 74, tool 10 performs as a standard frac plug where sealing ball 35 seats and unseats from ball seat 34 according to the pressure of communicated fluid from above. Removing solid plug 74 and contacting sealing ball 35 with ball seat 34 is simultaneous in the described embodiment.
Using
Thus, it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art, which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims.