In-Situ Stress Measurements at DOE'S Multi-Well Experiment Site, Mesaverde Group, Rifle, CO

摘要

Measurements of the vertical distribution of the minimum principal in situ stress in the lower Mesaverde group (7300 to 8100 ft depth) at DOE's Multi-Well Experiment site have been made by conducting small-volume, hydraulic-fracture stress tests through perforations. Accurate, reproducible results were obtained by conducting a number of repeat injections in each zone of interest using a specially designed pump system, modified high-resolution electronic equipment, and a down-hole shut-off tool with a bottom-hole pressure transducer. Stress tests were conducted in marine sandstones and shales as well as a 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 be dependent on lithology. Marine shales above and below the blanket sands have large horizontal stress - near lithostatic with a frac 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. On the other hand, sandstones and siltstones have much lower stresses with a frac 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 points were obtained from the paludal interval; no significant stress differences were observed in the different lithologies. 19 references, 8 figures, 1 table. (ERA citation 08:050693)