Reservoir Characteristics of Low-Permeability Sandstones in the Rocky Mountains

摘要: Understanding gas production from low-permeability sandstones requires an understanding of the in situ porosity, brine saturation, and effective permeability at reservoir saturation. Analysis data hundreds cores numerous western U.S. basins indicates that petrophysical properties well-defined lithofacies (or log-facies) are often unique within a narrow range. Diagenesis these commonly resulted destruction much original intergranular porosity left dissolved grains, clay-filled pores, sheet-like connecting pore throats. Pore throats or channels connect larger pores typically range size 1 to 0.1 micron represent only small portion total porosity. In most sandstones, is not significantly changed by confining stress changes, but permeabilities 10 1,000 times less than routine air permeability. The influence on can be attributed primarily decrease thin, tabular pores. Under stress, diameter up 50% 70% resulting decreases 40 times. Gas also rapidly 1% absolute values water saturations above approximately 40% 50%. "lrreducible" increase with decreasing permeability, and, 0.01 md "irreducible" dramatically. Cumulative flow storage capacity plots indicate very thin higher intervals yield large percentage cumulative capacity. Increased due drilling stimulation result lower unknowingly stabilized capillary pressure forces if pressures decreased. This type formation damage remedied increasing displace mobile water.