Influence of Paraffin on the Structure and Pore Characteristics of Solid Organic Matter

Abstract Paraffin, a naturally occurring macromolecular organic compound, is ubiquitously distributed in geological formations such as shale and coal seams. Its interaction with solid organic matter exerts a significant influence on the microstructure and pore architecture of host rocks, representing a critical geological process. To elucidate the underlying mechanisms of this interaction, this study systematically investigated the structural incorporation and pore-modifying behavior of paraffin within three representative high-molecular-weight organic geological substrates: kerogen, solid bitumen, and coal. A combined experimental approach integrating nitrogen adsorption and X-ray diffraction techniques was employed to characterize these interactions. The findings reveal that paraffin predominantly resides within the amorphous carbon fraction of host organic matter, where it enhances local crystallinity. However, its impact on pore networks varies markedly across different substrates: in kerogen, progressive pore reduction occurs via organic matrix swelling and paraffin precipitation. In contrast, excessive paraffin accumulation triggers pore segmentation in solid bitumen and, most notably, induces pore fracturing or splitting within coal, severely compromising pore connectivity. This study concludes that paraffin exerts the least influence on the pore connectivity of solid bitumen, and the most significant impact on coal. These insights bear direct implications for unconventional hydrocarbon systems. In shale gas reservoirs, the presence of asphaltene and solid bitumen may sequester paraffin, thereby mitigating damage to the porous matrix of kerogen. Conversely, in coalbed methane systems, paraffin effectively reduces the volume and connectivity of coal seam pores, resulting in significant adverse effects on gas production. Therefore, heating treatments may be required during exploitation to mitigate the detrimental impacts of paraffin accumulation.