Stress Changes in Thermal Operations

Abstract

Abstract Large-scale fracturing, fire floods, or hot water injection can alter principal stress magnitudes (σ1,σ2,σ3) and directions, even at the reservoir scale. In fracturing, this leads to changes in fracture orientation (Dusseault and Simmons, 1982); in firefloods, stress changes lead to yield and microseismic emissions, impairment of reservoir seal, and well loss through shear (Dusseault et al., 1988); hot or cold water injection can induce shear failure or tensile stress zones around the injection borehole (Hojka et al., 1993). Pore pressure changes also alter total and effective stresses (σ, σ’), and sand production or sand injection will lead to reservoir-scale stress changes (Dusseault and Santarelli, 1989). This article addresses stress changes during thermal operations. Thermal loading is often a non-linear problem because reservoir response is modified: principal stress fields are rotated and altered; volume changes occur and stresses change; yield and dilation of the reservoir occurs; absolute and relative permeability changes because of dilation and saturation alteration; bounding strata properties may be affected by tensile cracking or shear yield; and, overburden or reservoir shearing develops because of high pore pressures, thermal stresses, and weakening due to yield.