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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 drilling Horizontal new well infill drilling Horizontal 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.
Abstract As production from oil-bearing reservoirs matures, the need for enhanced oil recovery becomes increasingly important. In many of these reservoirs, waterfloods have been implemented and are presently approaching their economic limit in terms of producing water-oil ratio. One of the most important processes for revitalization of mature reservoirs is EOR by gas injection. Over the last 20 years, the authors have seen significant change in the approach to gas injection design and thus in the 1990's the oil industry has a greater understanding of gas EOR than ever before. This knowledge notwithstanding, many times operating companies jail to understand some of the complexities associated with appropriate gas injection design and consequently target reservoirs for gas EOR which may have characteristics which would preclude the reservoir from such EOR applications. This paper summarizes approximately two years work performed wherein effects of interfacial tension, viscosity ratio, gravity and wettability, all in the context of the microscale pore size distribution, have been evaluated. In particular, four reservoirs, wherein specific laboratory measurements including coreflood testing have been performed, are analyzed. Some counterintuitive responses are then described on the basis of these parameters. Finally, screening criteria for gas EOR projects has been proposed Three reservoirs which have been evaluated on a field scale are then ranked according to the screening criteria proposed herein. The approach used appears to confirm the response observed in the field thus lending credence to the gas EOR screening criteria developed in this paper. The objective of the screening criteria developed from this work is to allow an operating company to rank candidate gas injection EOR reservoirs according to that which has the most promise to that which has the least promise. In this manner, limited resources can be focused on that reservoir or reservoirs which are most likely to result in the best performance, thus stabilizing the reserves base for the corporation and allowing for more optimal corporate performance in the future. Displacement Paradigms In analyzing corefloods over the past fifteen years, the simple paradigm which has exhibited repeated efficacy is that which is described n the literature. Dullien described the features of importance in multiphase flow in porous media whereas many practitioners of reservoir engineering have tended to employ global observations to infer small-scale response, Chatsis, Diaz, Kwiecien et al, Kantzas et al and Ionnadis et al have focused on pore level to describe macro-scale performance. A host of other researchers has also contributed to the body of insightful literature which helps us to comprehend why porous media systems behave as they do. The domain of flow in porous media inheres of such challenging subjects that recently the pundits of the fractal domain have directed much attention to the treatment of the problems which were reserved, in previous decades, for the more pragmatic reservoir engineers. Feder, Mandlebrot and a host of others have begun to see flow in porous media as a pons asinorum to which fractal mathematics may hold an insightful eye.