Overview: Tight Reservoirs (October 2006)

High oil and gas prices provide a major boost to the development of tight and unconventional reservoirs. While most of this activity is in North America, tight and unconventional reservoirs are becoming more popular throughout the world. During the last year, I probably have seen more than a dozen conferences in North America on shale plays and unconventional reservoirs with increasing interest and participation from major operators. Success in unconventional reservoirs sometimes can be achieved only with "unconventional" thinking and approaches. The mix of "empirical" and "high-tech" engineering continues to provide an interesting and challenging work environment for engineers. A significant challenge in tight reservoirs is the proper completion of layered reservoirs. In some areas, operators are completing very thick, highly layered formations. The challenges begin with formation evaluation—What is actual pay? How do we optimize hydraulic-fracture staging and completion strategies to ensure coverage of all pay zones while minimizing cost? How do we evaluate which zones are contributing to production, and are we recovering all the reserves efficiently? In some areas, water-producing formations are interspersed with pay zones. How can these formations be avoided without sacrificing hydrocarbon production? There is one persistent question in tight reservoirs that continues to haunt engineers. How do we distinguish between completion effectiveness and reservoir performance? If a well underperforms, is it the result of a poorly performing hydraulic fracture, or is it just poorer-than-anticipated reservoir quality? This question is of high importance because it has major implications for well-completion optimization and infill-drilling strategies. More focus on the importance of gathering appropriate rock, reservoir, and hydraulic-fracturing data and application of advanced technologies hopefully will give us better answers to those questions. Tight Reservoirs additional reading available at the SPE eLibrary: www.spe.org SPE 100572 "A Study of Fracture-Initiation Pressures in Cemented Cased-Hole Wells Without Perforations" by G. Rytlewski, Schlumberger, et al. SPE 96104 "Optimal Stimulation Treatments in Tight Gas Sands" by S.A. Holditch, Texas A&M U., et al. SPE 100434 "Field Study of Completion Fluids To Enhance Gas Production in the Barnett Shale" by G.S. Penny, CESI Chemical, et al.