Coiled tubing drilling technology has advanced significantly over the last 2 - 3 years and while there are still questions, the technical feasibility of this technology is no longer questioned. Coiled tubing drilling technology may not be the technology of choice for drilling surface hole or for large diameter wellbores, except in exceptional cases, but may be the best technology for managing the drilling environment within the reservoir, especially in horizontal wells. The growing proliferation of "hybrid" drilling/coiled tubing rigs would tend to support this belief.
Since coiled tubing has typically been implemented as a live well intervention tool, this technology has always been linked with underbalanced drilling. However, crossroads have been reached and the process of implementing this technology in a commercially viable manner has begun. Of course, there is still a need for projects which push the envelope and help define the outer limits of the technology, but there is a growing need for the establishment of criteria to aid in the selection of the best technology to complete a given task.
One of the first steps to be completed is the technical feasibility study. This is the science of determining whether the underbalanced drilling objectives can be met within the framework of existing equipment.
The purpose of this paper is to discuss the cause and effect relationships of the independent and dependent variables which must be considered when performing a technical feasibility study, particularly when multi-phase flow is involved. Topics such as hole cleaning, weight on bit profiles and wellbore geometry are studied for their effects on drilling performance. The use of computer modeling is highlighted as a powerful tool to complete this initial study phase.
P. 181
