Minimum in-situ stress measurement using temperature signatures

Abstract

This study proposes a method to determine the temperature signature that can delineate the closure of a fracture, and infer closure stress from the bottomhole pressure that coincides with this signature. After shut-in, the fluid leaks off into the formation through an effective matrix comprised of native permeability and flow through natural or induced fractures. This flow from a conceptualized main fracture is accompanied by advective heat transfer away from the wellbore and advective movement of cooler fluid from the wellbore into the fracture. Considering the analog situation for pressure, the G function (a function defined by pumping and shut-in time) with temperature history has been used to account for the shut-in period. The change of temperature before and after fracture closure results in characteristic inflection points on a plot of GdT/dG vs G, suggesting closure of the primary fracture and providing an indication of the total stress normal to that fracture. Bottomhole temperature and pressure data were collected from a stress measurement program carried out in support of the Department of Energy's FORGE (Frontier Observatory for Research in Geothermal Energy) program. Eight cycles of injection were carried out in the barefoot section of well 58-32, a 2294 m deep vertical wellbore with a bottomhole static temperature of ∼199 °C. We compare the closure stresses inferred by temperature signatures with those determined from pressure signatures and find that these two sets of interpretations are close to each other. We also find that the temperature signatures are phenomenological and are less ambiguous than the pressure-G function signatures, making a temperature-G function analysis a valuable method for inferring the minimum in-situ stress.

Topics & Concepts