Petrophysical Texture Heterogeneity of Vesicles in Andesite Reservoir on Micro-Scales

It is of great significance to study the spatial distribution patterns and petrophysical complexity of volcanic vesicles which determine whether the reservoir spaces of the volcanic rocks can accumulate oil and gas and enrich high yields or not. In this paper, the digital images of three different textures of vesicular andesite samples, including spherical vesicular andesite, shear deformation vesicular andesite, and secondary filling vesicular andesite, are obtained by microscopic morphology X-CT imaging technology. The spatial micro-vesicle heterogeneity of vesicular andesite samples with different textures is quantitatively analyzed by fractal and multifractal methods such as box-counting dimension and the moment method. It is found that the shear stress weakens the spatial homogeneity since vesicles rupture are accelerated, elongated directionally, and connected with one another under the strain; the secondary filling breaks the vesicles, which significantly enhances the spatial heterogeneity. In addition, shear stress and secondary filling increase the complexity of vesicle microstructures characterized by different fractal and multifractal parameters. These conclusions will provide important theoretical and practical insights into understanding the degassing of volcanic rocks and prediction of high-quality volcanic reservoirs.