Wells – Processes – Assembling well part
Reexamination Certificate
1999-04-26
2001-06-19
Dang, Hoang (Department: 3672)
Wells
Processes
Assembling well part
C166S115000, C166S075110, C166S242600, C166S387000
Reexamination Certificate
active
06247537
ABSTRACT:
FIELD OF THE INVENTION
This application relates to seals for use in high pressure applications in corrosive environments such as well bores and, in particular, to a high pressure fluid seal for sealing against a bit guide in a well bore.
BACKGROUND OF THE INVENTION
The servicing of oil and gas wells to stimulate production requires the pumping of fluids under high pressure. It has now been demonstrated that it is advantageous to have full access, or substantially full access, to a well casing during a well stimulation treatment. Full access to the casing permits use of downhole tools which are often required, or at least very advantageously used, during a stimulation treatment. An apparatus for providing full access to the casing while permitting stimulation treatments at extreme pressures that approach a burst pressure rating of the casing is described in applicant's U.S. Pat. No. 5,819,851 which issued on Oct. 13, 1998 and is entitled BLOWOUT PREVENTER PROTECTOR FOR USE DURING HIGH PRESSURE OIL/GAS WELL STIMULATION. The patent describes an apparatus for protecting blowout preventers during well fracturing and/or stimulation treatments. The apparatus includes a hollow spool that has spaced-apart inner and outer sidewalls that define an annular cavity. The mandrel is forcibly reciprocatable in the cavity. The mandrel includes an annular seal at a bottom end for sealingly engaging a bit guide attached to the top end of the casing. The apparatus is mounted above a blowout preventer (BOP) attached to a casing spool of the well before well stimulation procedures are begun. The mandrel is stroke down through the BOP to protect it from exposure to fluid pressure as well as abrasive and/or corrosive well stimulation fluids, especially extreme pressures and abrasive proppants. The BOP protector provides a simple, easy to operate apparatus for protecting BOPs which provides full access to the well casing with well servicing tools to facilitate well stimulation at pressures approaching the burst pressure rating of the well casing.
The BOP protector has been readily accepted by the industry and has proven to be an effective tool which reduces the cost of well stimulation treatments while enabling an ultimate choice in treatment options. Field experience has shown that the bit guides of used wellheads tend to become deformed by small chips, dents or scratches after a period of running in and out with production tubing and/or downhole tools. Consequently, the annular seal described in U.S. Pat. No. 5,819,851 sometimes permits pressure leakage under high stimulation pressures.
There therefore exists a need for an improved seal structure for sealing against a bit guide in a well bore which ensures a leak-proof seal at elevated stimulation pressures.
It is therefore an object of the invention to provide an improved high pressure fluid seal for sealing against a bit guide in a wellhead.
It is a further object of the invention to provide a high pressure fluid seal for sealing against a bit guide in a wellhead which maintains an impervious seal when exposed to very high stimulation pressures.
SUMMARY OF THE INVENTION
The invention therefore provides a high pressure fluid seal for sealing against a bit guide in a wellhead, comprising in combination:
a mandrel adapted to be inserted into the wellhead, the mandrel having an inner wall defining a bore, an outer wall and an end for supporting an elastomeric seal, the end including an annular ridge which protrudes into the elastomeric seal to inhibit the seal from being extruded away from the bore when the elastomeric seal is seated against the bit guide and the bore is subjected to elevated fluid pressures.
In accordance with a further aspect of the invention, there is provided a method of performing a well stimulation process, comprising the steps of:
mounting a packoff assembly to an end of a mandrel used to isolate components of a wellhead mounted to the well from elevated fluid pressures used during the well stimulation process, the packoff assembly being adapted to be inserted into the wellhead with the mandrel, the packoff assembly having an inner wall defining a bore, an outer wall and an end for supporting an elastomeric seal, the end including an annular ridge which protrudes into the elastomeric seal to inhibit the seal from being extruded away from the bore when the elastomeric seal is seated against the bit guide and the bore is subjected to elevated fluid pressures;
inserting the mandrel into the wellhead and seating the elastomeric seal against the bit guide in order to isolate components of the wellhead form fluid pressures required for the well stimulation process; and
performing the well stimulation process.
The high pressure fluid seals for sealing against a bit guide in a wellhead in accordance with the invention are formed on a lower end of a mandrel which is inserted into a wellhead. The lower end of the mandrel includes at least one annular ridge that protrudes into the elastomeric seal to ensure that the elastomeric seal is not extruded away from the bore when the elastomeric seal is seated against the bit guide. The annular ridge provides an area of concentrated compressive force to compress the elastomeric seal against the bit guide so that an effective seal is achieved even when the bit guide is worn but still serviceable.
In accordance with a first preferred embodiment of the invention, the lower end of the mandrel is contoured to conform to the top surface of the bit guide and the annular ridge is positioned adjacent an outer wall of the mandrel end.
In accordance with a second preferred embodiment, an inner wall of a mandrel end extends downwardly past the bit guide to protect a top end of the casing from erosion by abrasives pumped into the well bore during a stimulation process.
REFERENCES:
patent: 1411486 (1922-04-01), Gallagher
patent: 1625378 (1927-04-01), Snodgrass
patent: 2187840 (1940-01-01), Penick
patent: 2867463 (1959-01-01), Snider
patent: 4602796 (1986-07-01), Setterberg
patent: 4907651 (1990-03-01), Bou-Mikael
patent: 5012865 (1991-05-01), McLeod
patent: 5819851 (1998-10-01), Dallas
Dang Hoang
Nelson Mullins Riley & Scarborough LLP
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