Understanding The Role Of Movable Oil In The Complexity Of Shale Pore Structures Based On Fractal Theory

Gaining a comprehensive insight into how shale’s pore structure changes due to the extraction of oil from smaller pores is pivotal for understanding the impact of movable oil in shale plays, particularly when estimating reserves. The fractal dimension, a parameter reflecting pore complexity, can be quantitatively employed to explore this aspect. In this research endeavor, we focused on assessing variations in pore structure resulting from oil removal in four samples from the Fengcheng shale Formation in Mahu Sag, China. To achieve this, we utilized two diverse probing techniques: Gas adsorption and small-angle X-ray scattering (SAXS). These methodologies allowed us to analyze pore structure alterations both before and after oil extraction. By comparing data gathered through these approaches, we calculated and compared fractal dimensions across pre- and post-extraction conditions. The outcomes revealed notable differences in fractal dimensions obtained from the two methods. Before extraction, the disparity in fractal dimensions calculated from these techniques ranged from 9.6% to 18.3% across the samples. Post-extraction, this variation decreased to a range of 1.6% to 25.1%. These differences originate from the inherent physics governing each method’s operational mode. Furthermore, both techniques indicated an increase in fractal dimension post-extraction, implying heightened pore complexity. In terms of the gas adsorption method, the increase in fractal dimensions across studied samples ranged from 6.385 to 13.435. Comparatively, for the SAXS method, this increase varied between 2.22% and 18.61%. These findings suggest that the movable oil, whether fully or partially occupying pore spaces or being adsorbed onto mineral/organic matter surfaces, could potentially reduce pore complexity. This study pioneers the role of adsorbed or freely moving oil within both connected and isolated pores of shale plays which is crucial for accurate reserve estimation and economic evaluation of shale plays. By elucidating the intricate interactions between oil and pore structures, our research lays the groundwork for more precise assessments in this critical domain.