Crosswell electromagnetic response in a fractured medium

Abstract

We experimentally verified that material-averaging techniques can be used for numerically modeling the response of the crosswell electromagnetic (crosswell EM) system in a fractured medium. We have designed a scaled model of the crosswell EM system, and verified that the laboratory data are in good agreement with the simulated response for different cases of fractures present in a host medium. Simulations of realistic scenarios in a hydrocarbon-filled reservoir indicate that the presence of fracture clusters can significantly affect the crosswell EM system response. The magnitude of the effect primarily depends on the number of fractures and their dip relative to the transmitter and receiver wells. In particular, small clusters of fractures filled with saline connate water produce large artifacts on the response, provided that the relative dip to the wells is large enough. The presence of a fracture cluster creates a characteristic signature in the full crosswell EM tomographical data set; therefore, crosswell EM data provides information related to the main fractures that are present between the wells. The inclusion of the fracture information as an additional constraint to the inversion of the crosswell EM data is expected to provide an improved interpretation of the reservoir fluids in the interwell space.

Discrete-dual-porosity model for electric current flow in fractured rock

“…Many, if not most, geophysical methods have been previously investigated to varying degrees in the context of fractured rock. These include seismic, ground-penetrating radar, electrical resistivity, induced polarization, self potential, and electromagnetic methods [e.g., Day-Lewis, 2003;Dorn et al, 2011Dorn et al, , 2012Donadille and Al-Ofi, 2012;Herwanger et al, 2004a;Krautblatter et al, 2010;Liu, 2005;Lofi et al, 2012;Lubbe and Worthington, 2006;Majer et al, 1997;Pytharouli et al, 2011;Queen and Rizer, 1990;Robinson et al, 2013;Schmutz et al, 2011;Tsoflias and Hoch, 2006;Talley et al, 2005;Wishart et al, 2008]. Here, we focus on the electrical resistivity method for the reasons that (i) a large body of previous work has indicated that the presence of fractures commonly has a significant influence on field geoelectrical measurements, especially as a function of direction or azimuth, and thus that these measurements may contain important information regarding the fracture distribution [e.g., Boadu et al, 2005;Busby, 2000;Lane et al, 1995;Taylor and Fleming, 1988]; (ii) geoelectrical measurements can be acquired in a straightforward manner along the Earth's surface and/or from boreholes in order to estimate the distribution of subsurface electrical resistivity at a range of spatial scales; and (iii) the presence of fractures in a rock represents preferential pathways for the flow of both water and electric current, which suggests that hydraulically relevant information on fracture network properties may be obtained from geoelectrical data.…”

Crosswell electromagnetic modeling from impulsive source: Optimization strategy for dispersion suppression in convolutional perfectly matched layer

“…Research on the crosswell EM commonly adopts magnetic dipole sources in a time-harmonic field 19 20 21 . In this research, the pulsed field with a magnetic dipole source is introduced into low-frequency crosswell EM modeling for enhancing transmit power 1 .…”

Long-Distance Crosswell EM Logging of Copper Ore Using Borehole-Surface Current Injection in Slim Holes

“…A crosswell EM system typically uses a magnetic dipole source as a transmitter deployed in the transmitter well to broadcast a time-varying magnetic field. A high-sensitivity magnetic probe that detects the EM field is deployed in the receiver well at a certain distance from the transmitting well [11]- [14]. Since a high-frequency EM wave attenuates too rapidly in the formation, low frequencies between 5 Hz and tens of kHz are generally used for crosswell detection [15]- [19].…”