Overview: Tight Reservoirs (November 2007)

Nothing has changed over the last year; high oil and gas prices are still providing a major boost to tight-reservoir development. However, costs have been rising because demand for services is high. North America has seen a "boom" of startup service companies that specialize in pumping hydraulic-fracture treatments. A surge of horizontal-well development in shale reservoirs is one of the reasons for the significantly increased demand for hydraulic-fracturing services. Instead of one fracture treatment per vertical well, horizontal wells are treated with up to a dozen individual fracture treatments in a short period of time requiring enormous amounts of water and fracturing materials on location. Moreover, in some cases, two to three offsetting horizontal wells are fracture treated simultaneously to achieve the best possible stimulation and drainage efficiency. In addition to "supertight" shale reservoirs, horizontal-well development also has moved back into the more traditional domain of tight-sandstone reservoirs, such as the Cotton Valley in east Texas and others. Significant advances in drilling efficiency and technology have been made as a result of this high activity, enabling high flexibility for well trajectories while providing a wellbore that meets the needs for the specific completion strategy. Horizontal-well completion strategies include mainly cased-and-cemented wells, but recently, uncemented laterals with openhole packers for stage isolation have become more popular because an entire wellbore can be fracture stimulated with back-to-back treatments in a single day. Diagnostic technologies, such as microseismic and tiltmeter fracture mapping and radioactive and chemical tracer logs, complement innovative drilling and completion technologies by providing a picture of what is happening during fracture treatments and showing how efficient the different completion technologies are in stimulating the entire horizontal wellbore. In conclusion, times are still exciting for tight reservoirs and likely will continue to be that way for many years to come. Tight Reservoirs additional reading available at the SPE eLibrary: www.spe.org SPE 102745 "4D Pressure Pilot To Steer Well Spacing in Tight Gas" by E. Quint, Shell E&P Americas, et al. [See JPT (February 2007) 86] SPE 108110 "Productivity and Drainage Area of Fractured Horizontal Wells in Tight Gas Reservoirs" by F. Medeiros, SPE, Petrobras, et al. SPE 102801 "Imaging Seismic Deformation Induced by Hydraulic-Fracture Complexity" by S.C. Maxwell, Pinnacle Technologies, et al. [See JPT (March 2007) 54]