نوع مقاله : مقاله پژوهشی
موضوعات
عنوان مقاله English
نویسندگان English
This study develops a comprehensive theoretical framework for quantifying frequency-dependent seismic attenuation in porous fractured carbonate rocks by integrating pore-scale microstructural characteristics with fluid saturation dynamics using the T-matrix approach. The model establishes an explicit connection between the hydraulic permeability tensor and ellipsoidal crack geometries, incorporating this relationship into a unified squirt flow formulation to predict both velocity dispersion and attenuation characteristics. Through systematic sensitivity analysis, the research demonstrates that permeability reaches maximum values in prolate-shaped cracks, while both attenuation patterns and velocity behavior are predominantly controlled by specific crack geometries and fluid composition properties. In single-phase fluid systems, increasing oil saturation produces elevated attenuation levels within typical logging frequency ranges of 1-20 kHz. In two-phase oil-gas systems, gas saturation below 20% induces substantial reduction in P-wave velocity along with increased attenuation effects, primarily resulting from significant compressibility contrasts between the fluid phases. The model validation utilized experimental data comprising five carbonate samples with complete petrophysical characterization. The inversion process for permeability estimation, employing a crack aspect ratio of 0.0001, demonstrated close alignment with experimentally measured values. Predicted quality factors (Q) showed strong correspondence with experimental attenuation measurements for homogeneous samples, though some deviations emerged in the heterogeneous sample where scattering effects presumably dominate over squirt-flow mechanisms. This research addresses a significant gap in existing models by establishing a direct microstructurally-based connection between permeability and dynamic squirt-flow response in fractured carbonate systems. The methodology advances beyond conventional approaches by incorporating the full permeability tensor derived from realistic pore geometries rather than relying on simplified scalar permeability values derived from empirical correlations. The results underscore the critical importance of incorporating pore shape frequency effects, and proper fluid substitution models into including attenuation for seismic data interpretation. The study acknowledges certain limitations in the current model, particularly its assumption of uniform fluid saturation and its inability to account for large-scale heterogeneities such as vugs and macro-fractures. These limitations are particularly relevant for complex carbonate reservoirs exhibiting multi-scale pore systems. Future work will focus on integrating patchy saturation effects for effective fluid modulus calculation, incorporating multi-scale pore inclusions representing different pore types, and combining the squirt-flow approach with scattering theory to better represent realistic porous-fractured environments. These enhancements will extend the model's applicability to more realistic geological formations. The framework presented here provides a foundation for developing more comprehensive rock physics models that can better address the challenges of characterizing heterogeneous carbonate formations through seismic attenuation analysis.
کلیدواژهها English
