Development and Implementation of a Slimhole Very-High-Dogleg Through-Tubing Rotary-Steerable Drilling System

Abstract

Abstract The maturing of many of the major oil fields around the world, combined with the drive to extend the life of assets and improve recovery rates, has led to significant interest in technology able to access bypassed oil and multiple small targets by achieving complex 3D well paths using Through Tubing Rotary Steerable Drilling (TTRSD) practices. The technology allows for reentry of existing wells and the enhancement of recovery by the drilling of one or more laterals from the existing well bore, while the completion and Xmas tree remain in place. Since the lateral is created deep in the existing well, the necessary distance, and drilling time, to the target are short and of comparatively low cost. Furthermore, since the existing completion remains in place, a costly re-completion is avoided. Assets will thus have production enhanced and utilization increased by quickly and efficiently getting access to additional reserves. In June 2006, Statoil (before the merge between Statoil and Hydro) and Schlumberger entered into a joint development program to build the systems suitable for TTRSD. The primary motivation for the program was to make a system that would enable drilling very high curvature well sections. This is important in TTRSD since the laterals are deep, and often in depleted reservoirs, making high doglegs quite critical in order to quickly steer away from water and other problem-zones. The new Very High Dogleg series of rotary steerable tools were developed in a size suitable to pass through existing completions in the North Sea, and communication technology was developed to allow transmission of near bit inclination and azimuthal information. During the period August-September 2008 the tool was successfully tested out in a Through Tubing Rotary Drilling (TTRD) operation in a well on the Gullfaks field on the Norwegian Continental Shelf, operated by StatoilHydro. The system provided, among other things, an average buildrate of 12,25°/30 m in the build section of the well. For the dimensions in question this is a significant improvement compared to existing Rotary Steerable Systems (RSS) systems.