The Description of Shale Reservoir Pore Structure Based on Method of Moments Estimation

• Published in: PloS one Vol. 11; no. 3; p. e0151631
• Main Authors: Li, Wenjie, Wang, Changcheng, Shi, Zejin, Wei, Yi, Zhou, Huailai, Deng, Kun
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 18.03.2016; Public Library of Science (PLoS)
• Subjects: Adsorption; Algorithms; Analysis; Biology and Life Sciences; China; Coefficient of variation; Data collection; Earth Sciences; Eigenvalues; Empirical analysis; Energy resources; Exploitation; Feasibility studies; Fractals; Geologic Sediments - classification; Geological Phenomena; Geology; Image analysis; Image processing; Laboratories; Mathematical analysis; Method of moments; Methods; Minerals; Natural Gas; NMR; Nuclear magnetic resonance; Oil and Gas Fields; Oil fields; Oil shale; Parameters; People and Places; Permeability; Physical Sciences; Pore size; Pore size distribution; Porosity; Radiation; Reservoirs; Sample preparation; Scanning electron microscopy; Shale; Shale gas; Shale oil; Shales; Size distribution; Skewness; Soil - chemistry; Structure; China; Sichuan Basin; Beijing China
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0151631

Shale has been considered as good gas reservoir due to its abundant interior nanoscale pores. Thus, the study of the pore structure of shale is of great significance for the evaluation and development of shale oil and gas. To date, the most widely used approaches for studying the shale pore structure include image analysis, radiation and fluid invasion methods. The detailed pore structures can be studied intuitively by image analysis and radiation methods, but the results obtained are quite sensitive to sample preparation, equipment performance and experimental operation. In contrast, the fluid invasion method can be used to obtain information on pore size distribution and pore structure, but the relative simple parameters derived cannot be used to evaluate the pore structure of shale comprehensively and quantitatively. To characterize the nanoscale pore structure of shale reservoir more effectively and expand the current research techniques, we proposed a new method based on gas adsorption experimental data and the method of moments to describe the pore structure parameters of shale reservoir. Combined with the geological mixture empirical distribution and the method of moments estimation principle, the new method calculates the characteristic parameters of shale, including the mean pore size (mean), standard deviation (σ), skewness (Sk) and variation coefficient (c). These values are found by reconstructing the grouping intervals of observation values and optimizing algorithms for eigenvalues. This approach assures a more effective description of the characteristics of nanoscale pore structures. Finally, the new method has been applied to analyze the Yanchang shale in the Ordos Basin (China) and Longmaxi shale from the Sichuan Basin (China). The results obtained well reveal the pore characteristics of shale, indicating the feasibility of this new method in the study of the pore structure of shale reservoir.