In-Situ Stress Measurements at U. S. DOE's Multiwell Experiment Site, Mesaverde Group, Rifle, Colorado

Vertical distribution measurements of the minimum principal in-situ stress in the lower Mesaverde group (7,300to 8,100-ft (2225- to 2470-m) depth) at the U.S. DOE's Multiwell Experiment (MWX) site have been made by conducting small-volume, hydraulic-fracture stress tests through perforations. Accurate, reproducible results were obtained by conducting repeated injections in each zone of interest with a specially designed pump system, modified high-resolution electronic equipment, and a downhole shut-off tool with a bottomhole pressure (BHP) transducer. Stress tests were conducted in marine sandstones and shales as well as in coal, mudstone, and sandstone in a paludal depositional environment; these tests provide a detailed stress distribution in this region. The stress magnitudes were found to depend on lithology. Marine shales above and below the blanket sands have large horizontal stresses that are nearly lithostatic, with a fracture gradient greater than 1.0 psi/ft (23 kPa/m). This indicates that these rocks do not behave elastically and processes such as creep and possibly fracturing are the dominant mechanisms controlling the stress state. Sandstones and siltstones have much lower stresses, with a fracture gradient of 0.85 to 0.9 psi/ft (19 to 20 kPa/m). Containment of hydraulic fractures would be expected under these conditions. Only three data pointsmore » were obtained from the paludal interval; no significant stress differences were observed in the different lithologies.« less