Impact of geochemistry on wettability and electrical properties of kerogen and organic-rich mudrocks
Authors: Jagadisan Archana 
Published: January 2025

The distribution of fluids in the pore space significantly affects the borehole electrical measurements such as resistivity logs, multiphase fluid flow and hydrocarbon recovery. Wettability is therefore an important factor impacting the water production and low resistivity pays in organic-rich mudrocks. Development of reliable models for hydrocarbon-in-place and water saturation estimation requires knowledge about wettability of mudrocks and the factors affecting it. A significant fraction of mudrock is composed of kerogen – insoluble organic matter in mudrocks – and therefore the properties of kerogen can considerably affect the mudrock properties. Studying rock physics and interfacial properties of kerogen remains an area of active research. Kerogen is often considered as hydrocarbon-wet in reservoir characterization. Despite this, wettability of kerogen is not fully understood and quantified. Assumptions made about the wettability of kerogen affects interpretation of borehole geophysical measurements such as electromagnetic measurements. It is therefore important to quantify wettability of kerogen as a function of relevant factors. For instance, the chemical structure and composition can vary as a function of kerogen type, which affects its surface properties such as wettability. In addition, processes such as thermal maturation induce changes in the chemical composition and structure. Thermal maturation decreases oxygen and hydrogen content and increases aromaticity. Oxygen containing function groups are also altered during thermal maturity. Moreover, changes in temperature and pressure also alter surface properties and affect the wettability of kerogen. However, the impact of different functional groups present in kerogen and reservoir temperature and pressure on kerogen wettability are yet to be quantified through a fundamental study. Molecular simulation studies can be used to understand the kerogen wettability for a wide range of chemical position of kerogen. In a previous work, molecular dynamics simulation was used to quantify wettability of kerogen. However, simplified kerogen structures were used which does not capture the heterogeneity and complexity of the kerogen structure. Moreover, there have been no studies which consider the impact of functional groups such as carboxyl and hydroxyl groups, and the impact of temperature and pressure conditions on the wettability of kerogen. There has been no previous experimental study to reliably determine wettability of pure kerogen, because of the challenges associated with kerogen isolation and with determining wettability of powders. I propose to use a combination of experimental and molecular simulation-based approaches to understand wettability of kerogen. First, the impact of composition and thermal maturity of kerogen on wettability of organic-rich mudrock will be studied using experimental and molecular simulation methods. The impact of reservoir temperature and pressure conditions on kerogwn wettability would be quantified using molecular dynamics simulations. The methods proposed in the thesis will help in improving the understanding of wettability of organic-rich mudrocks. The sensitivity of wettability of kerogen on the electrical resistivity measurements of organic-rich mudrock will be quantified using a combination of experimental methods and numerical simulation. This study could also provide insight into water production issues in shale and will potentially improve formation evaluation and the understanding of fluid flow mechanisms in organic-rich mudrocks.