Abstract

Hydraulic fracture containment is a critical factor in gas shale plays because a poorly contained hydraulic fracture can provide a pathway to an aquifer that can kill the well; conversely, internal stress boundaries within a gas shale may limit well performance. Fracture containment estimations use sonic and density logs to calculate Poisson’s Ratio (PR), Young’s Modulus (YME) and, ultimately, the minimum horizontal stress (sh). In the typical situation, where a vertical borehole intersects horizontal bedding, a conventional sonic log estimates mechanical properties only in the vertical dimension perpendicular to bedding. Shales, particularly organic-rich ones, are typically highly laminated. The presence of these laminae creates a rock fabric that may lead to differences in the sonic and mechanical properties parallel and perpendicular to them.

Application of an advanced sonic logging tool permits the calculation of shear slowness in three dimensions, including parallel to horizontal laminae. These results are used to calculate a Laminated Stress Profile (LSP) that includes PR and YME, both parallel and perpendicular to the laminae, and a sh that accounts for anisotropy. Calibration to core data is an essential ingredient for accurate calculations. The LSP sh is significantly different from that calculated using conventional methods in gas shale reservoirs, and it has been confirmed in multiple wells with stress measurements made by wireline testing.