RIASSUNTO
Abstract
Casing-while-drilling is a relatively new well construction process or technology for simultaneously drilling and casing a wellbore, and has been utilized globally over the last 15 years or so. This technology has shown advantages of reducing overall drilling time and cost. It has demonstrated signs of reducing hole problems, such as mud losses, through plastering effect because of the rotation of the casing string against the formation. It provides assurance to case off unstable formations while drilling, resulting in significantly reduced well construction costs.
Saudi Aramco has made several field test runs of this technology beginning in early October 2008, including deployments of both simple casing drilling with drill-through casing bit (non-retrievable) system and advanced bottom hole assembly (BHA) retrievable system designed for directional casing drilling. This paper will document the lessons learned from implementation of the technology, including planning and design, rig operations, problems encountered, modifications made to reduce risk after extensive review and investigation, and finally, successful deployment of a directional casing drilling to the planned casing point with a 17?? x 13-??? system. In addition, the paper briefly outlines the further required improvements of casing drilling tools to ensure continued success in the future.
Introduction
Drilling with casing or casing while drilling (CWD) is a relatively new well construction process in which standard casing is used as a drillstring to deliver rotary power to a drill bit. For the last decade or so the technology has evolved and gradually matured to address various drilling problems or challenges to the extent that it may drill from one casing shoe to the next casing shoe in a directional hole with a built section 1-5. The current casing drilling technology and field services are marketed by different levels of system designs, characterized by
Non-retrievable system
Retrievable BHA system
Liner drilling including retrievable and non-retrievable system
The non-retrievable system is the simplest, essentially consisting of a casing drill bit and casing string, but it has no directional trajectory change capability.
The retrievable system is an advanced casing drilling system that has directional trajectory change and logging capability with retrievable BHA capability for multiple runs per section while leaving casing string on the bottom. The system incorporates a special downhole latch and un-latch system to connect the downhole directional drilling assembly, made of bit, under-reamer, motor and or Rotary Steerable System (RSS), Measurement While Drilling (MWD)/Logging While Drilling (LWD), to bottom casing body with a profile nipple. To retrieve the BHA, either a drill pipe or wireline operation can be used, which allows simultaneous retrieval of the downhole BHA while independently reciprocating the casing string, to avoid sticking problems. The drillpipe retrieval system is simple, but leaves casing string static while running the stands of drillpipe. The wireline retrieval system is more advanced, but requires major changes to the rig top drive system and because of this, it entails a relatively high cost.