Application of Horizontal Drilling to Tight Gas Reservoirs

Abstract

Vertical fractures and lithologic heterogeneity are extremely important factors controlling gas flow rates and total gas recovery from tight (very low permeability) reservoirs. These reservoirs generally have in situ matrix permeabilities to gas of less than 0.1 md. Enhanced gas recovery methods have usually involved hydraulic fracturing; however, the induced vertical hydraulic fractures almost always parallel the natural fracture and may not be an efficient method to establish a good conduit to the wellbore. Horizontal drilling appears to be an optimum method to cut across many open vertical fractures. Horizontal holes will provide an efficient method to drain heterogeneous tight reservoirs even in unfractured rocks. Although many horizontal wells have now been completed in coalbed methane and oil reservoirs, very few have been drilled to exclusively evaluate tight gas reservoirs. The U.S. Department of Energy (DOE) has funded some horizontal and slanthole drilling in order to demonstrate the applicability of these techniques for gas development. Four DOE holes have been drilled in Devonian gas shales in the Appalachian basin, and one hole has been drilled in Upper Cretaceous tight sandstones in the Piceance basin of Colorado. The Colorado field experiment has provided valuable information on the abundance and openness ofmore » deeply buried vertical fractures in tight sandstones. These studies, plus higher gas prices, should help encourage industry to begin to further utilize horizontal drilling as a new exploitation method for tight gas reservoirs.« less