Wellhead bowl protector

The invention relates to apparatus for protecting wellhead bores during drilling operations, and more particularly to bowl protectors for preventing damage to wellhead bore seal surfaces as drilling equipment passes through the wellhead. The invention includes a bowl protector and a seperable false bowl for accepting a casing hanger, the bowl protector and false bowl being releasably connected together by shear pins.

BACKGROUND OF THE INVENTION 
This invention relates to apparatus for protecting wellhead bores during 
drilling operations, and more particularly to bowl protectors for 
preventing damage to wellhead bore seal surfaces as drilling equipment 
passes through the wellhead. 
A bowl protector comprises a generally elongated sleeve-like element that 
is traditionally installed temporarily in a wellhead bore to protect the 
bore sealing surfaces during a drilling operation. The bowl protector had 
to be removed, however, prior to running casing or tubing into the well to 
allow installation of the casing or tubing hangers in the wellhead. 
Removal of the bowl protector leaves the bore seal surfaces unprotected 
and thus highly vulnerable to damage by centralizers, casing collars and 
other equipment that must pass through the wellhead. This problem can 
become magnified in circumstances where the drilling rig is not perfectly 
centered over the well, a situation that occurs from time to time. 
SUMMARY OF THE INVENTION 
The present invention overcomes the foregoing problem by providing an 
assembly of a bowl protector and separable false bowl for accepting a 
casing hanger, the bowl protector and the false bowl being releasably 
connected together by shear pins. This assembly is run through the blowout 
prevent (BOP) and landed in the wellhead bore prior to running the casing, 
and an annular shoulder on the inner surface of the false bowl provides a 
seat for the casing hanger. The casing with its hanger is then run, the 
hanger landed on the seat in the false bowl, the hanger running tool 
retrieved, and a retrieving tool run and connected to the bowl protector. 
Upward pull applied to the bowl protector through the retrieving tool 
shears the pins and disconnects the bowl protector from the false bowl, 
facilitating retrieval of the bowl protector and continuance of drilling 
operations. If desired, the hanger running too can be provided with a 
latch mechanism to engage the bowl protector as the hanger is landed, 
whereby when the running tool is disconnected from the hanger the bowl 
protector can be separated from the false bowl and retrieved with the 
running tool by imposition of an upward pull on the running string, 
thereby avoiding a special trip to the wellhead to retrieve the bowl 
protector. 
Another advantage to the present invention is that it eliminates ned for 
reciprocation of the casing. Previous methods to retrieve the conventional 
bowl protector involved incorporating a tool in the casing string that 
latches in the protector as the string is lowered. The string then had to 
be pulled back to the rig floor to remove the protector and tool, thus 
requiring reciprocation of the casing downhold and thereby increasing the 
possibility of a stuck casing. 
The present invention results in the bowl protector having a dual function, 
namely to protect the bore in the wellhead and to serve as a running tool 
for the false bowl. Since the false bowl provides a smaller diameter seat 
for the casing hanger than the corresponding seat in he wellhead upon 
which the false bowl is supported, the outer diameter of the casing hanger 
can be reduced so that it drifts the inside diameter of the bowl 
protector. Another novel feature of the present invention is the provision 
of a system with a variable through bore, the larger bore incorporated in 
the wellhead design to allow passage of the drill bit and the smaller bore 
through the false bowl that allows passage of the casing string yet 
provides a seat or load shoulder for the casing hanger. 
Further advantages of the present invention will become apparent from the 
following description of the preferred embodiment, taken in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As seen best in FIG. 1, a bowl protector/false bowl assembly 10 according 
to the present invention comprises an elongated sleeve-like bowl protector 
12, an annular false bowl 14 of lesser axial dimension than the bowl 
protector 12, and a plurality of circumferentially spaced shear pins 16 
extending through the telescoped wall portions 18, 20 of the bowl 
protector and false bowl, respectively. 
The bowl protector 12 has an upper end portion 22 (FIGS. 2 and 3) of 
increased well thickness, and in this portion 22 are an outer annular 
groove 24 for receiving a plurality of circumferentially spaced lockdown 
screws 26 (only one shown), and an inner annular groove 28 for connecting 
the bowl protector to a retrieving tool (not shown). The lower end portion 
18 of the bowl protector has a reduced outside diameter 30 which fits 
inside the upper end portion 32 of the false bowl when these elements are 
assembled (FIGS. 1 and 2). 
The false bowl 14 has an outer annular shoulder 34 that lands on an inner 
annular seat 36 in the wellhead 38 (FIGS 2-4), the seat 36 thereby 
supporting the false bowl/bowl protector assembly 10 in the wellhead. The 
inner surface 40 of the false bowl includes an annular shoulder 42 that 
functions as a seat for a casing hanger 44 (FIGS. 3 and 4), the hanger 
having an outer annular shoulder 46 that lands on the false bowl shoulder 
42. The outer surface of the false bowl has a reduced diameter portion 48 
to minimize the relatively tight contact between the false bowl and the 
wellhead in that area yet leaving sufficient contact surface to assure 
proper centralization of the false bowl in the wellhead. 
INSTALLATION PROCEDURE 
The bowl protector/false bowl assembly 10 is installed by connecting it to 
a pipe string (not shown) and running it into the wellhead 38 until the 
shoulder 34 on the false bowl lands on the seat 36 in the wellhead. The 
lockdown screws 26 are then threaded inwardly into the bowl protector 
groove 24, thereby securing the assembly in functional position in the 
wellhead. The casing hanger 44 and attached casing string 50 are then run 
into the wellhead and the hanger shoulder 46 landed on the false bowl 
shoulder 42. Backing out the lockdown screws 26 from the bowl protector 
groove 24 frees the protector for retrieval that is accomplished by 
connecting onto the protector with a retrieval tool (not shown) and 
pulling up on the running string. This shears the shear pins 16, whereby 
the false bowl 14 remains in place in the wellhead (FIG. 4) and the bowl 
protector is retrieved to the drilling rig. 
Although the best mode contemplated for carrying out the present invention 
has been herein shown and described, it will be apparent that modification 
and variation may be made without departing from what is regarded to be 
the subject matter of the invention.