Extended Reach: New-Generation Frontier Drilling Rigs

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 19067, "Extended Reach: New-Generation Frontier Drilling Rigs," by F.J. Husband, SPE, George Bitar, SPE, and Mark Quinlan, SPE, Parker Drilling Company, prepared for the 2007 Offshore Technology Conference, Houston, 30 April-3 May. Common features of frontier development are fragile environment and high operating costs, which require unique operating methods. Planned well trajectories have departures and complexity such that feasibility risk is a critical part of the evaluation before investing in these projects. Primarily, this risk is determined on the basis of rig design and capacity to drill these extreme-reach well designs. Aspects of land-rig design, procedures, and operations that enable continued drilling of more-complex well trajectories with longer departures are discussed. Early Experience The original Prudhoe Bay multiwell development-drilling programs from small pad-based surface locations required directionally drilled well trajectories to reach the bottomhole targets. Bottomhole-assembly (BHA) technology and rig-hydraulic capacities enabled extended-reach drilling (ERD) with horizontal displacement at least twice that of vertical depth. The technique increased well productivity, limited environmental effects, and helped to avoid surface obstacles. Improved directional-drilling technology and departure limits enabled progressively smaller pad sizes. New rig designs were required to fit the rig on the site while allowing transportation access and simultaneous drilling and production activities. Elimination of pits and new cantilever designs were implemented to fit the rig between more-tightly spaced wellheads. Approximately 10 years ago in China, reserves from the Xijiang 24-3 offshore field in the South China Sea were upgraded after a revised seismic interpretation provided several new locations. However, the bottomhole locations required departures beyond technical limits at the time. By 2006, 13 ERD multilateral wells were drilled from Platform 24-3. One-of-a-Kind Projects The designing, fabricating, and operating of special-purpose drilling rigs for remote environments is unique, but all such projects have common features.Challenging well designExtreme environmentDifficult delivery conditionsConstrained exit conditions Sunkar Rig 257. This purpose-built rig was constructed on a unique shallow-draft arctic hull designed for drilling in extreme ice and wave conditions of the north Caspian Sea. It required year-round self-sufficient operations while drilling subsalt high-pressure/high-temperature sour-gas fractured formations by use of closed-circulation drilling techniques. Because of logistics, drilling environment, and operating regulations, these wells are among the most expensive in the industry, including deepwater wells. The unique design delivered significant benefits in executing the planned scope of work. However, it also restricts use of the vessel to regional programs without significant capital investment.