Abstract
Shale fracturing evaluation is of great significance to the development of shale oil and gas resources, but the commonly used shale evaluation methods (e.g., the method using the brittleness index based on mineral composition or elastic parameters) have certain limitations. Fractures and beddings affecting fracturing are not considered in these methods. Therefore, it is necessary to develop a new method to evaluate fracturing more comprehensively. The samples used in this research were taken from four typical continental shale basins of China, namely the Bohai Bay Basin, the Ordos Basin, the Songliao Basin, and the Junggar Basin. From a microscopic point of view, a three-parameter evaluation method involving multi-dimensional factors has been developed based on the nanoindentation method. Then, the fracturing coefficient K2 is obtained by combining the ratio β of the fracture indentation to the total indentation and the uneven coefficient m. After that, the fracability coefficient K3 is the ratio of the elastic modulus parallel to bedding to that perpendicular to bedding. Finally, the correlation between fracability coefficients K1, K2, and K3 is used to evaluate the overall fracturing performance of shale. The results of this evaluation method are in good agreement with the actual fracturing performance. It can be concluded that this method is highly reliable and practical and well worthy of promoted applications.
Highlights
With the increasing demand for oil and gas resources all around the world, shale oil has become a key field for the exploration and development of unconventional oil and gas resources globally
In 2013, some scholars developed a fracability evaluation method using three rock mechanical parameters, namely the Young’s modulus, Poisson’s ratio, and uniaxial tensile strength, as the independent variables, and the fracability coefficient as a dependent variable, which yet ignored the impact of mineral composition (Yuan et al, 2013)
In 2014, some scholars proposed a comprehensive evaluation method for shale gas fracability, which uses a radar chart of six geomechanical parameters to rank the fracability of shale gas reservoirs
Summary
With the increasing demand for oil and gas resources all around the world, shale oil has become a key field for the exploration and development of unconventional oil and gas resources globally. In 2014, some scholars proposed a comprehensive evaluation method for shale gas fracability, which uses a radar chart of six geomechanical parameters to rank the fracability of shale gas reservoirs. This method cannot be used for quantitative analysis (Zhao et al, 2015). In 2015, some scholars proposed an evaluation method for shale gas fracability by integrating three features of shale (the brittleness, fracture toughness, and natural weak plane), but the impact of rock mechanical parameters was not addressed (Chen et al, 2017).
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