RIASSUNTO
Abstract
The modern era of coiled tubing drilling began in mid-1991. Since then, upwards of 300 wells or sections of wells have been drilled using coiled tubing. The majority of these applications has used conventional coiled tubing service units in conjunction with a workover hoist or conventional rig to complete portions of the program. A few modified units have been used to perform re-entry drilling work. The first horizontal re-entry conducted entirely using a hybrid coiled tubing service unit has been described by Eide et al 1.
During 1996, two fit-for-purpose ""reeled systems"" were commissioned. The reeled system concept embraces the surface equipment, downhole directional drilling system and the man/machine interface into one integrated package. These systems integrate the benefits of continuous tubing, the ability to snub into live wells and the option to rotary drill using drill pipe. The systems have been designed for use with coiled tubing and or jointed pipe over a range of applications from re-entry drilling, underbalanced drilling and field maintenance.
This paper describes, through a review of the benefits of coiled tubing drilling, the background to the development of these systems. A description of the process followed from initiation to commissioning of the reeled systems is also provided. A case history of the first use of coiled tubing drilling techniques in the Gulf of Mexico is discussed.
Introduction
If there is one constant within the oil industry it is the need to reduce costs. This was as true in the 1950s as it is today. During the past 15 years, significant improvements in the drilling process have contributed to reducing cost per foot and to increasing the range of drilling opportunities. These improvements include the use of Measurement While Drilling (MWD) tools, steerable motors and PDC bits. Production improvements have been realised by the global implementation of horizontal drilling techniques. There have also been ""productivity"" improvements by virtue of the oversupply of drilling rigs and the consequent low day rate.
However, the development of innovative systems cannot be hindered by what is a short term anomaly in the pricing structure of conventional rigs. The development of innovative technologies will continue, and from this the range of options available to the petroleum engineer will increase.
As described by Faure et al 2, the drilling and completion industry is still tied to the paradigm of the 10 metre joint with all its inherent drawbacks. Technology improvements based on this paradigm are unlikely to provide more than marginal improvements in drilling productivity. Drilling in the new millennium will involve developing marginal and satellite fields, sustaining field life, moving into deep water and high pressure high temperature reservoirs. This will require the use of innovative techniques. The vision of a reeled system allows the engineer to break away from the 10 metre joint paradigm to match purpose and function and provide a solution to these and other economic and technical challenges.
The complete reeled system vision includes the use of reeled tubulars for drilling, completion, recompletion, pipelines and as a replacement for conventional jointed liners and casing. Coiled tubing is the embryonic form of the reeled system, and coiled tubing drilling the first and important step in the implementation of the reeled system.
Coiled Tubing Drilling
Coiled tubing first saw use in the oil industry in the mid-1960's but suffered from poor service quality. In recent years, improvements in pipe quality and a better understanding of coiled tubing pipe limitations (fatigue and mechanical failure) have led to a dramatic increase in the use of coiled tubing for performing workover and completion services 3. Coiled tubing is now available in sizes to 5"". The common coiled tubing sizes used for drilling applications are 2"", 2 3/8"" and 2 7/8"".