Modeling the effects of microscale fabric complexity on the anisotropy of the Eagle Ford Shale

Abstract

Microscale fabric influences the elastic properties of rock formations. The complexity of the microscale fabric of shale results from composition, platy clay minerals, kerogen, and their preferred orientation patterns. This microscale fabric is also the likely cause of the elastic anisotropy of the rock. In this paper, we have developed a comprehensive three-step rock-physics approach to model the anisotropic elastic properties of the Upper Eagle Ford Shale. We started with anisotropic differential effective medium modeling, followed by an orientation correction, and then a pressure adjustment. This method accounts for the microscale fabric of the rock in terms of the complex composition, shape, and alignment of clay minerals, pore space, and kerogen. In addition, we accounted for different pressure-dependent behaviors of P- and S-waves. Our modeling provides anisotropic stiffnesses and pseudologs of anisotropy parameters. The modeling results match the log measurements relatively well. The clay content, kerogen content, and porosity decreased the rock stiffness. The anisotropy increases with kerogen content, but the influence of clay content was more complex. Comparing the anisotropy parameter pseudologs with clay content shows that clay content increases anisotropy at small concentrations; however, the anisotropy stays constant, or even slightly decreases, as the clay content continues to increase. This result suggests that the preferred orientation of clay clusters is preserved at low clay concentration but vanishes at high clay concentration. This method could also be applied to other shales with carefully chosen parameters to model anisotropic elastic properties.

Study on Anisotropic Petrophysical Modeling of Shale: A Case Study of Shale Oil in Qingshankou Formation in Sanzhao Sag, Songliao Basin, China

“…Figure 18: Porosity cross-section of SYY3, XU12, and XU13. 19 Geofluids linear, which provides a theoretical basis for the construction of shale rock physical cross-plot template (3) Based on the shale rock physical model and the analysis of elastic parameter influencing factors, the elastic parameters λρ and μρ sensitive to organic matter and pores are optimized, and the shale rock physical cross-plot template that can distinguish different organic volume fractions and porosity is constructed (4) The application shows that the predicted Vs based on the proposed model is in good agreement with the Vs derived from dipole source logging. Through prestack elastic parameter inversion, the "sweet spot" characteristics are well described, which provides an important support for the deployment of shale oil wells in Sanzhao sag…”

“…In shale oil exploration and development, geological "sweet spot" evaluation and optimization are important foundations. The successful development of shale oil in the United States is due to the improvement of geological understanding and engineering technology progress, and the most important one is the ability to identify a "sweet spot" [4]. The "sweet spot" of shale oil refers to the reservoir intervals with more oil and better physical properties under the overall oilbearing background.…”