Decommissioning of Splitter Wellhead Wells

Abstract

Drilling keeper wells with an open-sea concept by suspending a 36″ conductor to a jackup drilling rig as a temporary structure induced several criticalities in plugging and abandoning the wells. The severity amplified with the two (2) wells are cemented inside the conductor and completed with a splitter wellhead. As per the Malaysia local regulatory, any abandoned wells are to be free from any structure protruding from seabed. This is paramount in confirming the drilled location is free from potential hazards. This splitter design confirmed that conventional cut-and-pull approach is not feasible and multistring cutter is the only solution available. This paper covers the approach and result in performing eccentric cut of fully cemented 2 × 9-5/8″, 2 × 13-3/8″ and a 1.0″ wall thickness 36″ conductor including decommission of a splitter wellhead. In achieving the objective to P&A the keeper wells, an Abrasive Water Jet Cutter (AWJC) is deployed to perform an internal eccentric cut that able to penetrate five (5) cemented casing simultaneously. The cutter is paired up with Drilling Wire Saw (DWS) and Dual Drilling Machine (DDM) as a surface cutter and a "hole-borer" in cutting the retrieved multistring into shorter sections that eliminated the needs to dismantle the splitter wellhead into individual component. Meanwhile, for surface lifting and suspending, an engineered pad eyes, H-beam and lifting frame with pins were required to guarantee a successful operation. AWJC is designed to penetrate structures with extreme pressure, coupled with optimized pre-planned nozzle rotation speed to establish a complete 360° clean cut downhole. The jetting mechanism using the right mixture of water and garnet is crucial in providing sufficient capability to penetrate the conductor size in an eccentric condition considering the worst-case position of the cutter downhole. The significant finding from this P&A operation is understanding the type of garnet and fluid less environment around nozzle cutter head as main contributors for an efficient cutting process. Actual pick-up weight to pull free the pipe was 37% higher than the calculated weight for a complete cut. Hence, the surface capability shall be designed with some marginal tolerance to provide additional lifting capability in case an unsmoothed cut is experienced. Overall, the operation managed to overcome the challenges and uncertainties experienced and mark as a great milestone for the first ever decommission splitter well design in Malaysia.