Formation Pressure as an Indicator of High Stratigraphic Permeability

Abstract

Reservoir and economic modeling shows that stratigraphic reservoirs with transmissivities of 3 – 10 Darcy-meters at 3 – 4 km depth and at temperatures of more than 175°C should be suitable for 100+ MWe-scale power developments, and have a levelized cost of electricity of about 10c/kWh. One question about stratigraphic units at this depth is whether the potential reservoirs could be over-pressured. An evaluation of hundreds of formation pressure data derived from drill stem tests in oil exploration wells in prospective basins of the western U.S. shows that in the Great Basin, pressures everywhere are hydrostatic to the total depth of wells. This is interpreted as widespread lateral permeability beneath individual basins with short-circuits to the near-surface at the basin flanks and in the adjacent ranges. Formation pressure trends in deep wells that penetrate high-permeability Mississippian carbonate units beneath the Paradox Basin (Utah), and a part of the Piceance Basin (Colorado) and the northern Wind River basin (Wyoming) all show hydrostatic pressure from near-surface despite over-pressures in low permeability units above the carbonates, and depths exceeding 6 km. In the case of the Paradox basin, the Mississippian has the same pressure profile over an area of 104 km2, and appears to be in equilibrium with the Colorado River. Possibly a normally-pressured, hydrostatic condition in deep stratigraphic units is an indicator of laterally extensive high-permeability.