The present invention relates in general to an improved wellbore fracturing system, and in particular to an improved wellhead fracture isolation system.
One type of treatment for an oil or gas well is referred to as well fracturing or a well “frac.” Typically an operator connects an adapter to the upper end of a wellhead member such as a tubing head and pumps a liquid at a very high pressure down the well to create fractures in the earth formation. The operator will also then disburse beads or other proppant material in the fracturing fluid to enter the cracks to keep them open after the high pressure is removed. This type of operation is particularly useful for earth formations that have low permeability but adequate porosity and contain hydrocarbons, as the hydrocarbons can flow more easily through the fractures created in the earth formation.
The pressure employed during the frac operation may be many times the natural earth formation pressure that ordinarily would exist. For example, during a frac operation the operator might pump the fluid at a pressure of 8,000 to 9,000 psi, whereas the normal pressure in the wellhead might be only a few hundred to a few thousand psi. Because of this, the body of the wellhead and its associated valves typically may be rated to a pressure that is much lower than what is desired for frac operations. While this is sufficient to contain the normal well formation pressures, it is not enough for the fluid pressure used to fracture the earth formation. Thus, the wellhead and associated valves may be damaged during frac operations.
Moreover, because of the proppant material contained in the frac fluid, the frac fluid can be very abrasive and damaging to parts of the wellhead. To allow the operator to use a pressure greater than the rated capacity of the wellhead seals (including the various valves associated with the wellhead) and to protect against erosion resulting from the frac fluid being pumped at high pressure and volume into the well, the operator may employ an isolation sleeve to isolate these sensitive portions of the wellhead from the frac fluid. An isolation sleeve seals between an adapter above the wellhead and the casing or tubing extending into the well. The sleeve isolates the high pressure, abrasive fracturing fluid from those portions of the wellhead that are most susceptible to damage from the high pressures and abrasive fluids used in well fracturing operations. However, even with the use of an isolation sleeve, unacceptable levels of tensile stress may be induced in the hub section of the wellhead. It is desirable to reduce these tensile stresses in the wellhead.
An isolation sleeve is carried by a running tool or an adapter assembly for insertion into the bore of a wellhead or tubing head. The wellhead is the surface termination of a wellbore and typically includes a casing head for installing casing hangers during the well construction phase and (when the well will be produced through production tubing) a tubing head mounted atop the casing head for hanging the production tubing for the production phase of the well. The casing in a well is cemented in place in the hole that is drilled. The fluids from the well may be produced through the casing or through production tubing that runs inside the casing from the wellhead to the downhole formation from which the fluids are being produced.
The isolation sleeve may be configured to be installed and retrieved from the wellhead by a running/retrieval tool. The tool can be lowered through a double studded adapter connected to the tubing head and frac valve if installed. Lockdown screws may be used to maintain the isolation sleeve within the tubing head during fracturing operations.
A washer and split ring assembly is utilized at a hub or flange section at an upper portion of the tubing head. The washer is axially located between the flange and nuts threaded onto the studs or bolts of the adapter, which run through the flange. The ring is radially located between the washer and the tubing head body. The ring may have a tapered outer shoulder that contacts a corresponding shoulder on the washer such that when the nut is tightened, at least a portion of the tightening force is transmitted via the washer and ring to the flange of the tubing head. The force induces a compressive stress on the flange that advantageously counters the tensile stresses experienced by the flange section during fracing operations.
The interface between the adapter plate and the tubing head flange may also be modified to counter the tensile stresses experienced during fracing operations. An inner shoulder may be formed on a lower end of the adapter plate that protrudes further downward than an outer shoulder of the adapter plate. Both inner and outer shoulders contact the upper end of the flange of the tubing head when the adapter is fully made up with the flange. During tightening of the adapter bolts, the inner shoulder will first contact the upper end of the flange. Because the inner shoulder is radially disposed a distance “r” from the bolt axis, a moment is advantageously created that acts as a preload that must be overcome by the tensile stresses. At final bolt torque, the outer shoulder contacts the flange to serve as a stop and prevent further movement of the adapter.
These features advantageously counter the unacceptable tensile stresses induced on the flange of a tubing head during well fracturing operations.
An isolation sleeve 18 is shown installed within the bore 13 of the tubing head 10 to protect the tubing head 10 from the high pressure and abrasive fluids imposed during a well fracturing operation. The pressure during fracturing operations can be significantly higher than the rating of the wellhead 10 and associated components such as valves. Thus, isolation sleeve 18 and packoff bushing 14 are rated for pressures above 5000 psi normal working pressure. A lower end of isolation sleeve 18 may be inserted into an upper receptacle 30 on an upper end of the packoff bushing 14 having an upward facing shoulder 32. An anti-rotation key 34 located on the lower end of packoff bushing 14 that interferes with a slot 36 formed in tubing head 10 to prevent the packoff bushing 14 from rotating if the isolation sleeve 18 is installed within the packoff bushing 14 by threading or a Back Pressure Valve (BPV) (not shown) is made or removed from the packoff bushing 14. The bore of the packoff bushing 14 below the shoulder 32 may be prepared with a threaded profile to receive a BPV. Further, a downward facing shoulder 40 located in the recess of the wellhead member 10 interferes with an upward facing shoulder 42 located on the outer surface of the packoff bushing 14 to limit the upward movement of the packoff bushing 14 within the wellhead member 10. In this example, lockdown screws 44 engage a groove 46 formed on an exterior surface of the isolation sleeve 18 to maintain the isolation sleeve 18 in place during fracturing operations. The tapered shoulder 32 prevents the lower end of the isolation sleeve 18 from coming into contact with the top of the production casing 12 to thereby create a gap between the two well components.
Continuing to refer to
A gasket 52 provides a seal at the interface between a flange 66 of the tubing head 10 and an annular double-studded adapter (DSA) 60 having a bore diameter that can accommodate the outer diameter of the isolation sleeve 18. The DSA 60 comprises a plate 61 and may be provided with test ports (not shown) to allow detection of potential leaks. A set of threaded studs 62 each secure to threaded holes of the DSA 60, and protrude upward and downward from DSA 60. The studs 62 projecting downward may be of a different size than studs 62 projection upward. The lower ends of studs 62 extends through holes in an external flange 66 of tubing head 10 and secure DSA 60 to tubing head 10 with nuts 64. A washer and reinforcement ring assembly 70 may be located between the nut 64 and a lower surface 72 of the flange 66 to provide a compressive load that counters tensile stresses experienced at the flange 66 during fracing operations. The washer and ring assembly 70 will be discussed in more detail in a subsequent section. The upper studs or bolts 62 of the DSA 60 allow additional equipment, such as a frac valve 80, to be mounted to an upper portion of the DSA 60. An annular gasket 82 may be utilized at the interface between a flange of the frac valve 80 and the DSA 60.
Referring to
In general, during fracing operations, pressure from the high pressure fracturing pushes against frac valve 80 (
In another embodiment of the invention, illustrated in
While the invention has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.
Number | Name | Date | Kind |
---|---|---|---|
5341885 | Bridges | Aug 1994 | A |
5540282 | Dallas | Jul 1996 | A |
6179053 | Dallas | Jan 2001 | B1 |
6289993 | Dallas | Sep 2001 | B1 |
6364024 | Dallas | Apr 2002 | B1 |
6470965 | Winzer | Oct 2002 | B1 |
6516861 | Allen | Feb 2003 | B2 |
6666266 | Starr et al. | Dec 2003 | B2 |
6817423 | Dallas | Nov 2004 | B2 |
7055632 | Dallas | Jun 2006 | B2 |
7066269 | Dallas et al. | Jun 2006 | B2 |
7069987 | Kwasniewski et al. | Jul 2006 | B2 |
7308934 | Swagerty et al. | Dec 2007 | B2 |
7614448 | Swagerty et al. | Nov 2009 | B2 |
20030205385 | Duhn et al. | Nov 2003 | A1 |
20060017287 | Milberger | Jan 2006 | A1 |
20070102926 | Magnier et al. | May 2007 | A1 |
20090211749 | Nguyen et al. | Aug 2009 | A1 |
Number | Date | Country |
---|---|---|
2195118 | Jul 1998 | CA |
2276973 | Mar 2000 | CA |
0117417 | Sep 1984 | EP |
2009088674 | Jul 2009 | WO |
Entry |
---|
GB Search Report dated Mar. 29, 2012 from corresponding Application No. GB1202196.0. |
Number | Date | Country | |
---|---|---|---|
20120205111 A1 | Aug 2012 | US |