Abstract
In recent years, the Yanchang shale-oil formations of the Ordos Basin are rich in reserves with complex lithology and structure characteristics, low porosity and low permeability, and weak anomalies for oil and water discriminations, have been the key targets of unconventional oil/gas resource exploration and development in the relevant areas. The joint acoustic-electrical (AE) properties can be used to interpret reservoir lithology, mineralogy, pore structure, and fluid saturation. To conduct tests of thin section analysis, X-ray diffraction, and ultrasonic and electrical experiments at different pressures and saturation degrees, cores from the shale-oil formations in the Q area of the basin are collected. The variations in AE properties with respect to clay content, porosity, pressure (microfracture), and saturation are analyzed. The experimental results indicate that the rock physics behaviors of sandstones with different clay contents vary significantly. The AE properties of clean sandstones are basically dependent on the microfractures (pressure), while for muddy sandstones, the clay content is an important factor affecting the responses. The target reservoir consists of interbedded sandstone and shale layers. The AE equivalent medium equations and the Gurevich theory are applied to establish the joint models for the different lithologies and simulate the variations in AE properties with respect to fluid type, pore structure, and mineral components. The three-dimensional joint templates of clean and muddy sandstones, as well as shale, are developed based on the elastic and electrical attributes and then calibrated using the experimental and well-log data. The reservoir properties are estimated with the templates and validated by the log data. The results indicate that the joint templates based on lithology characteristics can effectively characterize the properties of interbedded sandstone and shale layers. Furthermore, the combined application of AE data provides more beneficial information for the assessment of rock properties, leading to precise estimates that conform with the actual formation conditions.
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Acknowledgments
We thank Dr. Han Xuehui of the China University of Petroleum (East China) for his assistance in the experimental tests. This work is supported by the National Natural Science Foundation of China (Nos. 41974123, 42174161), the Jiangsu Innovation and Entrepreneurship Plan and the Jiangsu Province Science Fund for Distinguished Young Scholars (grant no. BK20200021).
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Pang Meng-Qiang received his B.S. in Geological Engineering from Tianjin Chengjian University in 2017. He is presently a Ph.D. student in the School of Earth Sciences and Engineering at Hohai University. His research interests are rock physics model, reservoir prediction and acoustic and electrical properties.
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Pang, MQ., Ba, J., Wu, CF. et al. Acoustic-electrical properties and rock physics models for shale-oil formations: prediction of reservoir properties of interbedded sandstone and shale layers. Appl. Geophys. 19, 485–502 (2022). https://doi.org/10.1007/s11770-022-0949-z
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DOI: https://doi.org/10.1007/s11770-022-0949-z