The Influence of Magnetic Minerals on Induced Polarization Measurements in Sedimentary Rocks

• Published in: Geophysical research letters 2022-10, Vol.49 (19), p.n/a
• Main Authors: Peshtani, Klaudio, Weller, Andreas, Saneiyan, Sina, Slater, Lee
• Format: Article
• Language: English
• Subjects: Capacitance; Carbonates; Contaminants; Fluid flow; Fluids; formation factor; Grain size; Groundwater; Induced polarization; Iron; Low concentrations; Magnetic permeability; Magnetic properties; Magnetic susceptibility; Magnetism; Mathematical models; Mineralogy; Minerals; Parameter identification; Parameters; Polarization; pore geometry; Sandstone; Sedimentary rocks; specific capacitance; Stewardship; Susceptibility; Sustainability
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL100192

Induced polarization (IP) measurements in porous sedimentary rocks are modeled in terms of pore geometrical descriptors (PGD). Using an extensive data set composed of 241 sandstone, carbonate, and arenite samples, we identified a stronger relationship between IP parameters and volumetric magnetic susceptibility versus IP parameters and PGD. This finding suggests that even small concentrations of iron minerals in rocks typically thought to lack electron‐conducting minerals can significantly influence IP measurements. The combination of magnetic susceptibility with a pore geometrical descriptor term improves the empirical prediction of IP measurements relative to the use of pore geometrical descriptor terms alone. This suggests that small concentrations of iron minerals exert a strong control on the specific capacitance, a property that remains poorly understood. The lack of any relationship between magnetic susceptibility and the PGD confirms that the magnetic susceptibility provides additional information unrelated to PGD. Plain Language Summary Geophysical measurements such as induced polarization (IP) provide essential information about the properties that control the flow and transport of fluids, including groundwater and contaminants, in the subsurface. Understanding such subsurface processes is critical to efforts to promote environmental sustainability and stewardship. IP measurements are thought to be primarily controlled by the geometry of the interconnecting pores of sedimentary rocks, as quantified by parameters such as the surface area or grain size. Such sedimentary rocks are usually assumed to be devoid of electron‐conducting minerals. By measuring a simple property known as the magnetic susceptibility, we find that low concentrations of magnetic minerals in these sedimentary rocks influence IP measurements just as much, if not more than, the pore geometrical descriptor terms that appear in empirical and physical models for IP. This finding suggests that models describing the IP signatures in sedimentary rocks need to consider mineralogy. Key Points Only 38% (at most) of the variation in the induced polarization (IP) signal is predictable from pore geometrical descriptors (PGD) The magnetic susceptibility, a parameter unrelated to PGD, exerts a stronger influence on IP data Using magnetic susceptibility to constrain variations in the specific capacitance improves IP models from pore descriptors