Borehole to Surface Electromagnetic Monitoring of Hydraulic Fractures

Modeling electromagnetics on cylindrical meshes with applications to steel-cased wells

“…In other cases, the most significant physical property variations may conform to a cylindrical geometry, for example in settings where vertical metallic well-casings are present, or in the emerging topic of using geophysics to "look ahead" of a tunnel boring machine. In particular, understanding the behavior of electromagnetic fields and fluxes in the presence of steel-cased wells is of interest across a range of applications, from characterizing lithologic units with well-logs (Kaufman, 1990;Kaufman and Wightman, 1993;Augustin et al, 1989), to identifying marine hydrocarbon targets (Kong et al, 2009;Swidinsky et al, 2013;Tietze et al, 2015), to mapping changes in a reservoir induced by hydraulic fracturing or carbon capture and storage (Pardo and Torres-Verdin, 2013;Börner et al, 2015;Um et al, 2015;Weiss et al, 2016;Hoversten et al, 2017;Zhang et al, 2018). Carbon steel, a material commonly used for borehole casings, is highly electrically conductive (10 6 − 10 7 S/m) and has a significant magnetic permeability ( ≥ 100 µ 0 ) (Wu and Habashy, 1994); it therefore can have a significant influence on electromagnetic signals.…”

“…Similarly, Ronczka et al (2015) considers the use of groundwater wells for monitoring a saltwater intrusion and investigates numerical strategies for simulating casings as long electrodes. Imaging hydraulic fractures has been a motivator for a number of studies at DC or EM, among them Weiss et al (2016); Hoversten et al (2017). Some of these have suggested the use of casings that include resistive gaps so that currents may be injected in a segment of the well and potentials measured across the other gaps along the well (Nekut, 1995;Zhang et al, 2018).…”

Finite-element analysis of top-casing electric source method for imaging hydraulically active fracture zones

“…Accordingly, they would be vulnerable to cultural noises. In such cases, one may need to consider downhole based methods presented in Hoversten et al (2017).…”

“…As shown in Table 1, we do not consider directly modeling micro-scale facture networks. Rather, the thickness of the fracture networks is artificially inflated into 1m thick HAFZ in a volume-averaged sense as done in Weiss et al (2015) and Hoversten et al (2017). The inflation approach is geophysically reasonable when the low resolution of the electrical method and the distance between source/receiver and HAFZ are considered.…”

“…reasonable. However, knowledge of both the fluid injection location and the amount of the injected fluid helps us to estimate a possible maximum volume of the imaging domain (Hoversten et al, 2017).…”