Unconfined and triaxial stress tests were conducted on dry and saturated shale from El Paso's Wagon Wheel No. 1 well. The material tested is in general a very competent shale containing stringers of silt and sand, producing local inhomogeneities which effect unconfined fracture, but do not significantly effect the behavior at higher mean normal pressures. Strong sensitivity of deviatoric maximum stress to mean pressure is observed for dry material, while little increase in deviatoric strength with pressure occurs for the fully saturated material. Dilation accompanies distortional deformation; however, softening or ease of compaction occurs at small distortional strains, before substantial dilation begins. In detail, the deviatoric stiffness (apparent shear modulus) and the pressure-volume relation (compressibility) are stress state and stress path dependent, while the deviatoric strength path dependent, while the deviatoric strength is only stress state dependent.
Mechanical properties of a shale material were obtained for El Paso Natural Gas Company to be used in shock calculations to determine rock breakage, and hence increased permeability, caused by nuclear explosion. The samples tested were taken from a core at the 10,215–10,216 foot depth in El Paso's Wagon Wheel No. 1 well, NW/4 Section 5, Township 30N, Range 108W, Sublette County, Wyoming. Small samples were dry cored from the large core provided by El Paso and tested unconfined and provided by El Paso and tested unconfined and confined to pressures of 6 kbars. Both dry and fully saturated samples were tested, parallel and perpendicular to the large core parallel and perpendicular to the large core axis. Petrofabric analysis was made and photomicrographic observations taken to photomicrographic observations taken to predict and better understand the mechanism predict and better understand the mechanism of fracture.
Similar tests were previously conducted for El Paso on a large core of sandstone from 10180.4–10181.0 foot depth. These results are reported in Terra Tek report "Testing Program Conducted for El Paso Natural Gas Company" August, 1970.
Test techniques are similar, and were described in detail in the previous El Paso report, and in other reports, and will therefore only briefly be covered here.
