In-Situ Stress Measurements at DOE'S Multi-Well Experiment (Englisch)

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 downhole shut-off tool with a bottom-hole pressure transducer. Stress tests were conducted in marine sandstones and shales as well as coal, mudstones, and sandstones in a paludal depositional environment; these tests provide a detailed stress distribution in this region. The stress magnitudes in blanket morphologies were found to be dependent on lithology. Marine shales above and below the blanket sands have large horizontal stresses - near lithostatic with a frac gradient greater than 1.0 psi/ft. On the other hand, sandstones and siltstones have much lower stresses with a frac gradient of 0.85 to 0.9 psi/ft. Containment of hydraulic fractures would be expected under these conditions. Stress tests conducted in the paludal interval gave frac gradients of approximately 0.88 to 0.98 psi/ft with no significant stress differences in various lithologies (sand, silt, mudstone, coal). Significant out-of-zone fracturing should be expected for hydraulic fracture treatments conducted in this interval. Two open-hole stress tests were conducted in a blanket sandstone to determine the orientation of the fractures, estimate the maximum principal in situ stress, and check the accuracy of the measurements through perforations. Maximum stresses were found to be about 400 psi greater than the minimum stress at a depth of 7500 to 7550 ft. 12 references, 5 figures, 1 table. (ERA citation 08:055461)

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