Characterization of the poro-mechanical properties of synthetic coquinas using 3D imaging techniques

Abstract This study aims to investigate the influence of the state of stress surrounding carbonate coquinas rocks, which act as reservoirs for oil and gas, and how it affects their poro-mechanical properties. This understanding is crucial for well production and injection in oil and gas systems. Due to the difficulty and expense of obtaining representative samples from natural formations, this research focuses on a novel approach to developing synthetic coquinas to replicate and analyze these rocks’ stress behavior and properties under various stress conditions. Three synthetic coquinas (S1, S2, S3) were prepared using natural aragonite materials and shell fragments to simulate the natural heterogeneity of carbonate coquinas. Each sample was prepared inside an oedometer cell, coupled with a microtomograph to apply oedometric compressive stresses. These samples were then analyzed using X-ray microtomography and pore network modeling to analyze their properties, and microstructural changes under different stress conditions. The porosity of all samples decreased significantly under stress, with reductions of 87.5% for S1, 70.0% for S2, and 85.9% for S3. Initial millidarcy (mD) permeability values of 33.10 mD (S1), 11.60 mD (S2), and 22.90 mD (S3) dropped to zero as pressure increased. This indicates that the coquinas lost the ability to allow fluid flow under high stress. Compared to literature studies, the synthetic coquinas proved efficient and reproducible to represent carbonate coquinas with some similar properties. This study presents a reproducible, cost-effective method for creating synthetic coquinas, providing new insights into the stress surrounding carbonate formations and enhancing understanding of petroleum reservoirs.