A stuck 9?-in. 10,000 psi Inconel 925 back pressure valve (BPV) required a specialized testing apparatus to validate the mill design. The 18?-in. Unihead and compromised BPV mandated an ice plug freeze capable of withstanding a 10,000 psi test as a well control barrier on the high-pressure sour gas well. The development, testing process and field results to mill the BPV and apply the ice plug freeze will be presented. Mill machine lathe tests were conducted to achieve preliminary cutting structure and the mill profile. The test apparatus simulated milling an 8.635-in. Inconel 925 BPV stuck in a 9?-in. Inconel 725 tubing hanger. A test stand with 26-in. outside diameter (OD) casing and 9?-in. inner casing were constructed and double wrapped with 500 ft. of ?-in. helical coil to simulate the freezing of an 18?-in. Unihead, with 10,000 psi pressure integrity inside the 9?-in. tubing.
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