Crosswell electromagnetic tomography: System design considerations and field results

Abstract

Electrical conductivity is an important petroleum reservoir parameter because of its sensitivity to porosity, pore fluid type, and saturation. Although induction logs are widely used to obtain the conductivity near boreholes, the poor resolution offered by surfacebased electrical and electromagnetic (EM) field systems has thus far limited obtaining this information in the region between boreholes. Low-frequency crosswell EM offers the promise of providing subsurface conductivity information at a much higher resolution than was previously possible. Researchers at Lawrence Livermore National Lab (LLNL) and Lawrence Berkeley Laboratories (LBL), together with an industrial consortium, recently began a program to conduct low-frequency crosswell EM surveys and develop suitable inversion techniques for interpreting the data.In developing the field instrumentation we used off-the-shelf components whenever possible, but cus-

Fracture Propagation, Fluid Flow, and Geomechanics of Water-Based Hydraulic Fracturing in Shale Gas Systems and Electromagnetic Geophysical Monitoring of Fluid Migration

“…After a number of sources are excited at different positions in one well, and the magnetic fields are measured at a number of receiver positions in the other well, the conductivity structures between the wells are imaged through inverse modeling. (For details of the crosswell EM methods and their applications, the reader is referred to Alumbaugh and Morrison (1995), Wilt et al (1995), Zeng et al (2000), and Gao et al (2008).) To successfully sense and monitor injectionfluid migration pathways, conductivity changes caused by migration should produce measurable perturbation in the magnetic fields.…”

Environmental management science program FY1997 progress report

“…Effective in-situ remediation requires a knowledge of subsurface porosity, permeability, and fluid saturation Only after the site has been chatacterized can the clean-up begin Using geophysical techniques to image the subsurface is much cheaper and less invasive than drilling many sampling wells Electrical methods have usually been used fat environmental applications, but recent advances in high-resolution crosswell seismic methods (e g , Hanis et al , 1995) suggest that combined electrical and seismic techniques could be a powerful tool for imaging the shallow subsurface Surface and borehole geophysical data have been used for a number of Yeats for site characterization and clean-up monitoring (e g , , 1995, Wilt et al , 1995a and monitoring steam-flooding in hydrocarbon reservoirs (e g ? Harris, 1988;Mathisen et al , 1995), but these data may only indirectly measure the site structure and fluid flow parameters that control the storage and movement of subsurface fluids The current practice in geophysics is to interpret a single geophysical data set to obtain an image of a single geophysical parameter, such as seismic velocity or electrical resistivity The geologic parameters of interest (i e., the permeability, porosity, and fluid distribution) are usually estimated by overlaying a series of these geophysical images Current esttmation techniques are very subjective, and geologic parameters ate not obtained directly Current practices also do not exploit the complementary capabilities of seismic and electrical methods Seismic methods are best for resolving subsurface structure and porosity (e.g , Lines et al, 1993, Mathisen et al, 1995, whereas electrical methods ate preferred fat identifying fluids, saturation, and permeability (e g , Wilt et al , 1995a,b).…”

Co2 Capture Project - An Integrated, Collaborative Technology Development Project for Next Generation Co2 Separation, Capture and Geologic Sequestration

“…The SEG special issue 'Crosswell Methods' contains several papers on the application of crosswell seismic tomography specifically for thermal process monitoring and several others on crosswell EM monitoring of water floods. Wilt et al (1995) report on the application of crosswell EM in water flood monitoring. .…”

“…The majority of effort, as measured by the topics of published and presented work, has concentrated on developing and improving algorithms for estimating the geophysical parameters themselves (Newman, 1995;Lazaratos et al, 1995;Wilt et al, 1995;Nemeth et al, 1997;Goudswaard et al 1998 to list but a few). In most applications where nongeophysical parameters, such as temperature during a steam flood (Lee et al, 1995) or CO 2 saturations during CO 2 flood Wang et al, 1998) are the object of the crosswell survey, correlations between the geophysical parameters, e.g., velocity or electrical conductivity, and the desired reservoir parameter are derived and used to infer the distribution of reservo ir parameters from the distribution of the geophysical parameters. The output from the survey is still most commonly a cross section of velocity, electrical conductivity or the time-lapse change of these parameters, which is then interpreted in terms of its implications for the distribution and/or change of the parameter of interest (temperature, CO 2 saturation, etc.…”