Modelling induced polarization effects due to pyrite in geochemical alteration zones above hydrocarbon accumulations

Abstract

Geoelectrical methods measure resistivity and induced polarization (IP) effects in the subsurface. The differentially normalized electromagnetic method (DNME) detects geochemical alteration zones due to anomalous electrical responses which are often located above a hydrocarbon accumulation. Leakage above a non-perfect top seal is postulated to change the pH in the overlying sediments where a shallower mobility barrier is encountered. Epigenetic pyrite mineral growth is stimulated when iron and sulfur ions are available. Leakage and mineral growth are modelled by mathematical formulae assuming diffusion migration through the overburden. Effects of time and tectonic faulting are examined. Pyrite is highly polarizable and easily detected by an electrical IP survey in the field, whereby a current is introduced into the ground and subsequently turned off. Decay of the potential difference over the receiver electrodes is monitored in time. Special parameters facilitate detection of IP anomalies related to the presence of hydrocarbons. An inverted electrical depth model is computed using the Cole–Cole formula. The impact of geochemical modelling and predicted epigenetic mineral growth is demonstrated for the Severo-Gulyaevskaya dataset (Siberia). The overall DNME track record shows a reduced risk attached to hydrocarbon prospects, with a more reliable ranking at reasonable costs.

Quantifying Induced Polarization of Conductive Inclusions in Porous Media and Implications for Geophysical Measurements

“…The formulation of the IP response from first principles presented here will enable development of structure-property relationships that can be used in partial-differential-equation based forward models and inversions, without resorting to empirical formulations that have made interpretation of induced polarization parameters difficult and subjective 1 . Furthermore, our discovery on the scaling of porous conductor suggests that a long relaxation time (~1 s) is a unique feature in sedimentary rocks containing nano-porous sulfides such as pyrite, which strongly correlates with the activity of sulfate reducing bacteria and hydrocarbon occurrence 6,7,14,15,43 . In addition to the broad geophysical applications, our discovery also leads to new strategies for surface area characterization of porous materials, super-capacitor design from biomimetic processes, and bio-inspired materials 47 .…”

“…As a key electromagnetic-based geophysical exploration method [1][2][3][4][5] , induced polarization (IP) has been widely utilized in field-scale geophysical surveys for many decades [6][7][8][9] to provide information about the complex conductivity (chargeability) of subsurface formations filled with ionically conducting fluids. These surveys supplement controlled-source electromagnetic 2 and magnetotelluric 1,5 surveys, which generate subsurface resistivity maps.…”

“…There are two distinct, commonly recognized mechanisms that give rise to complex conductivity in this low-frequency regime 4 : (1) diffusive relaxation of neutral modes associated with ionic concentrations, usually called "membrane polarization", and (2) capacitive charging of the electric double layer on the surfaces of non-ionic conductors, usually called "electrode polarization". Regardless of the dominant mechanism, frequency dependence of complex conductivity is typically fitted to a Cole-Cole type model 10 as the basis of various geophysical exploration methods [6][7][8][9][11][12][13][14][15][16][17][18] , where the effective complex conductivity of the porous media σ eff has the form 16 :…”

Identification of induced polarization of submarine hydrocarbons in marine controllable source electromagnetic exploration

“…However, marine CSEM usually only considers electromagnetic induction but ignores the IP effect. The IP effect can occur in the reservoir due to various factors (Veeken et al, 2009), so considering the IP effect as well will make the modeling more reasonable and therefore give more accurate results when interpreting and processing the data (Veeken et al, 2012;Xu and Sun, 2018). We have used the integral equation method for modeling, adopted the scattering and superposition methods to calculate the dyadic Green's function required in the study, replaced the real resistivity with a complex resistivity that takes into account the IP effect, investigated the response patterns of different ion polarization models, and analyzed the influence patterns of various model parameters.…”

Three-dimensional modeling of IP effects in time-domain electromagnetic data

“…This property can be of particular value when exploring for disseminated mineralization in which chargeability is commonly the most diagnostic physical property. Recently, studies have explored other potential applications, such as hydrocarbon exploration (Davydycheva et al, 2006;Veeken et al, 2009aVeeken et al, , 2012, environmental and groundwater studies (Slater and Glaser, 2003), and various engineering applications (Kemna et al, 2004;Okay et al, 2013).…”