Quantifying the Impacts of Thermal Maturity on Elastic Properties of Kerogen
- Clotilde Chen Valdes (Texas A&M University) | Zoya Heidari (The University of Texas at Austin) | Andres Gonzalez (The University of Texas at Austin)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 58th Annual Logging Symposium, 17-21 June, Oklahoma City, Oklahoma, USA
- Publication Date
- Document Type
- Conference Paper
- 2017. copyright held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
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Direct measurements of elastic properties of kerogen using static methods is challenging due to its small concentration and complex distribution within organic-rich mudrocks. Furthermore, the effects of thermal maturity on elastic properties of kerogen are not well understood. The primary objective of this paper is to quantify the impact of thermal maturity on elastic properties of kerogen. We measure elastic properties of isolated kerogen samples, at the micron-scale level of investigation. We perform nanoindentation tests on compacted kerogen samples at different levels of synthetic thermal maturation. Then, we quantify the impact of kerogen thermal maturity on effective elastic properties in mudrocks. We also evaluate the relationship between elastic properties, hydrogen index, and electrical resistivity in the synthetically-matured kerogen samples.
We first performed kerogen extraction from organic-rich mudrock samples using chemical and physical techniques without changing chemical structure of kerogen. We then used mechanical compaction to create solid disks of isolated type II and type III kerogen samples. We synthetically matured the kerogen samples using heat treatment to obtain kerogen samples at four different levels of thermal maturity. Nanoindentation mechanical tests were then performed on kerogen samples using minimal overburden load to obtain the Young’s modulus and hardness of each sample. Finally, we performed sensitivity analysis to quantify the impact of thermal maturity and variation of kerogen elastic properties on effective elastic properties of the rock.
Results showed that Young’s modulus varies as a function of thermal maturity of kerogen. Young’s moduli of kerogen samples initially decrease as the thermal maturity increases and then start to continuously increase. This pattern is consistent with electrical conductivity of the samples. The initial decrease in Young’s modulus can be due to elimination of water molecules from the samples. At higher heat-treatment temperatures, the increase in Young’s moduli can be explained by changes in kerogen structures, including increase in aromaticity and graphitization. The outcomes of this paper enable a better understanding of the effects of thermal maturity of kerogen on its mechanical properties in organic-rich mudrocks. The measured mechanical properties can help to create a database of static elastic properties of kerogen at different burial depths and thermal maturation levels. Furthermore, the results can potentially improve well-log-based assessment of rock mechanical properties in formations with high organic content.
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