Addressing Challenges Associated with Image Interpretation in Geothermal Wells
University of Auckland
Time & Place
Thu, 25 Feb 2021 16:00:00 NZDT in ER 263
Borehole imaging technology provides a detailed and depth accurate picture of the distribution of fractures and, depending on the tool type, rock textures at the wellbore wall. It also generates the data required to model stress orientation and magnitude. Consequently, borehole imaging has been pivotal for research into the mechanisms controlling the distribution of permeability in wells. However, the technology is rarely deployed in high-temperature (>240°C) geothermal wells because of perceived and real operational hurdles. Furthermore, images are often subject to reduced coverage and resolution because rugose and oversized borehole conditions are common in productive geothermal wells. Given the geometric sample bias associated with observing a 3D fracture network along a line and how thermally-enhanced hoop stresses locally distort the number and aperture of fractures at the wellbore wall, these images may poorly reflect conditions even 10s of cm into the reservoir. Finally, depending on permeability magnitude, pressure and fluid state, feedzones in geothermal wells vary in response to changes in operating conditions. Studies comparing geologic observations to feedzones rarely address this issue nor do they include attempt to quantify permeability magnitude or fluid state. This seminar will introduce these interpretation challenges, describe how addressing them improves our ability to identify possible geologic controls on the distribution of feedzones, and discuss borehole image examples from Muara Laboh and Rantau Dedap in Sumatra and Ngatamariki and Wairakei in the Taupō Volcanic Zone.
Irene is a PhD student at University of Auckland.