Horizontal Re-entry Drilling With Coiled Tubing: A Viable Technology

Abstract Horizontal drilling technology has been the fastest growing segment of the oil and gas industry over the last few years. With the diversity of reservoirs in the Western Canadian Basin, Canada is widely recognized as a leader in this technology. Due to economic, environmental and surface logistics concerns, re-entry drilling from existing wellbores is often an extremely viable solution to horizontal development in existing reservoirs. By utilizing an existing wellbore, many of the costs can be avoided and often troublesome formations are already secured behind casing. Coiled tubing drilling is also a fast growing technology in Canada, and the obvious advantages of coiled tubing for a safe, efficient drilling operation which lends itself easily to "underbalanced" or "live well" operations have propelled it into the horizontal re-entry market. This paper examines the rationale behind the selection of coiled tubing as a viable drilling technology for horizontal re-entry drilling. A summary of the field trials is also included along with a discussion on the current focus of technology development. OBJECTIVES: Accelerate production of Mannville pools in Southern Alberta. Improve total recovery within economic limits. Determine most cost effective technology for reservoir management. Take advantage of royalty relief schemes available under current regulatory structure. TECHNOLOGY EVALUATION Why horizontal re-entries? The selection of coiled tubing underbalanced drilling as a reservoir management tool to enhance economics of pool development was arrived at after consideration of the above objectives. The primary technology options available were as follows:Vertical infill drillingHorizontal new well infill drillingHorizontal re-entry drilling The above options could further be divided into overbalanced and underbalanced drilling techniques and could be conducted with conventional jointed pipe drilling technology or coiled tubing drilling technology. The overall economics of re-entering an existing well and drilling a horizontal wellbore versus drilling a new vertical or new horizontal well were projected to favour the horizontal re-entry. The elimination of requirements for lease acquisition allow for a more cost effective and timely reservoir development scheme. The royalty schedule for reentry drilling offers additional incentive over new drills in this area. Old marginal wells do not recover reserves in place before economic limits are reached. Horizontal drilling was expected to provide better reservoir access, improved drainage efficiency and an improved recovery factor. Why underbalanced drilling? The reservoir in question consists of tight sandstone with low permeability and porosity and depleted pressure. As a result, these wellbores are difficult to clean up with post-drilling stimulations. Fonnation damage problems can be circumvented by maintaining underbalanced conditions while drilling. Sample quality with underbalanced drilling is enhanced due to turbulent flow and samples are returned to surface faster, thus providing good geological control for geosteering. Real-time reservoir evaluation through production testing while drilling provides another useful tool to monitor reservoir performance or save on completion costs for unproductive reservoirs.