Safeguarding Pressure Integrity of Surface Well Control Equipment: A Review of Fastlock Drilling Adapter and Blow Out Preventer Connection Failure in High Pressure Well

摘要

Well control is primarily achieved using mud hydrostatic column to overbalance reservoir pressures. The overbalance from mud can be lost in a well due to following reasons; encountering unexpected higher pore pressure, reduction in mud column due to down hole losses, reduction in mud weight due to dilution and loss of hydrostatic head due to poor drilling practices. Emergency situation is created when escalation of any of the scenarios results to the loss of primary well control. In such instance, the secondary well control equipment such as blow out preventers and wellheads are activated to enable restoration of overbalance and return of drilling operation to normalcy. As part of emergency preparedness, it is important to regularly confirm the pressure integrity of the secondary well control equipment in order to guarantee their availability whenever required. As part of the pressure integrity assurance process in Shell operations, pressure test of the critical equipment is mandatorily carried out every 21days whenever the wellbore is exposed to hydrocarbon bearing reservoir. Drilling operation has been successfully carried on GXH-1 HPHT well across the hydrocarbon bearing hydrostatic interval. Pressure test that was carried out on the well control equipment after installing the 9 7/8" production casing and prior to drilling into the high pressure interval of the well revealed loss of pressure integrity at the flange connection between the 15,000psi rated BOP and fastlock drilling adapter on the 15,000psi rated wellhead. Upon observation, the loss of pressure integrity was discovered to be due to washout on the flanges of the BOPs and the wellhead as well as the ring gasket. The well was suspended with plug to allow safe repairs of the damaged flanges. The damages on the flanges were successfully repaired and pressure tested to full rated working pressure before recommencement of drilling operation. This paper reviews the relevant drilling operations that preceded the loss of pressure integrity of the secondary well control equipment and the root cause analysis carried out on the failure. It also enumerates recommendations from lessons learnt from the incident that will ensure prevention of future re-occurrence of the type of failure.