Quantifying the Effect of Kerogen on Electrical Resistivity Measurements on Organic-rich Source Rocks

Interpretation of electrical resistivity logs in organic-rich source rocks has been challenging for petrophysicists. Conventional resistivity-porosity-saturation models (e.g., Archie?s, Dual-Water, and Waxman-Smits equations) assume that saline water is the only conductive part of the formation. However, this assumption is not reliable in organic-rich source rocks in the presence of highly mature organic matter, clay, and pyrite. Previous experimental studies indicate that aromaticity of kerogen increases with an increase in thermal maturity, which might lead to conductive behavior of kerogen. In this thesis, I investigated and quantified the effect of conductive kerogen on electrical resistivity of organic-rich source rocks.

First, I investigated the reliability of conventional resistivity-porosity-saturation models in the assessment of fluid saturations in organic-rich source rocks using well logs and core measurements in the Haynesville shale-gas formation. Next, I numerically simulated electric field, electric currents, and electrical resistivity of pore-scale images of organic-rich source rocks. I quantified the effect of (a) volumetric concentration of kerogen, (b) kerogen conductivity, and (c) spatial connectivity of kerogen-water network on electrical resistivity of rocks using pore-scale numerical simulations.

Well-log interpretation of the Haynesville shale-gas formation showed conventional resistivity-porosity-saturation models underestimate hydrocarbon saturation by 20% - 40% in the zones with high volumetric concentration of kerogen. In this thesis, I showed that the error in estimates of hydrocarbon saturation could be due to the impact of kerogen on electrical resistivity measurements. Pore-scale numerical simulations confirmed that conventional resistivity-porosity-saturation models could lead to 10% - 23% improvement in estimates of hydrocarbon saturation if the impact of conductive kerogen is taken into account. Results of this thesis act as the first step towards improving conventional resistivity-porosity-saturation models for estimation of fluid saturations in organic-rich source rocks.