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Wellhead Casing Seal Bore for Stage Wellhead Isolation Tool
This document describes a wellhead casing seal bore for a stage wellhead isolation tool installed above a well production casing at the surface and attached to the bottom of the wellhead. The device allows a stage wellhead isolation tool (stage WIT) seal mandrel to seal in the device to completely isolate and protect the wellhead surface equipment from stimulation treatment fluids and pressures. The device allows downhole tools to be conveyed through the ID of the Stage WIT seal mandrel while it is rigged up on a wellhead during multiple stage stimulation treatments that are known to the industry.
The device maintains the same practice of attaching the wellhead to the production casing as known to the industry. The device is connected to the top of the production casing at surface, hung off in the wellhead casing hanger, and the wellhead casing head installed on top of the device, see Figure 1. The device is installed at the time of well completion for the purpose of performing multiple stimulation treatments on the well.
Figure 2 shows the device. The wellhead casing seal bore for Stage WIT is an extension of the casing and must meet or exceed the casing pressure and tensile strength ratings. The device has an ID at the top end to accommodate the stage WIT seal mandrel OD. As an example, Figure 2 shows the device with 5-1/2 inch 17 lb/ft casing ID of 4.892 inches, the ID can accommodate the stage WIT seal mandrel OD. The device transitions down to an ID to match the production casing ID connected to the bottom of the device; for example 5-1/2 inch, 26 lb/ft casing, with 4.548 inch ID. The device connects to the production casing with a m...