In summary, as at April 2009 when the H1 Well had been suspended and the West Atlas rig had departed from the Montara WHP to undertake other work, not one well control barrier in the H1 Well had been satisfactorily tested and verified, and one barrier that should have been installed was missing. In other words, the H1 Well was suspended without regard to PTTEPAA’s own Well Construction Standards or sensible oilfield practice.
When the West Atlas rig returned to the WHP in August 2009 it was discovered that the 13⅜ ” PCCC had never been installed. The absence of this PCCC had resulted in corrosion of the threads of the 13⅜” casing and this, in turn, led to the removal of the 9⅝” PCCC in order to clean the threads. This was viewed by PTTEPAA personnel as a mere change of sequence that simply involved bringing forward the time of the removal of the 9⅝” PCCC. PTTEPAA’s Well Construction Manager, Mr Duncan, took a positive decision not to reinstall the 9⅝” PCCC. This meant that, according to PTTEPAA’s operational forecast and drilling program, the H1 Well would have been exposed to the air without any secondary well control barrier in place for some 4 to 5 days, with sole reliance on an untested primary barrier (the cemented 9⅝” casing shoe) that had been the subject of significant problems during its installation.
After the 9⅝” PCCC had been removed, the H1 Well was left in an unprotected state (and relying on an untested primary barrier) while the rig proceeded to complete other planned activities as part of batch drilling operations at the Montara WHP. The Blowout in the H1 Well occurred 15 hours later.
In the petroleum industry, well integrity is ensured by always having built in redundancies (secondary barriers) to safeguard against a blowout. Unfortunately, in the H1 Well there were no tested and verified barriers in place