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Comprehensive Brittleness Evaluation on Cap Rock of X9 Gas Storage Using an Improved Geometric Polygon Method

Brittleness is an important mechanical characteristic of rock and is critical to shale reservoir, which is characterized with low porosity and low permeability. Brittleness evaluation of cap rock plays an important role in the site selection, operation, and maintenance of underground gas storage. However, it is still a difficult problem for conducting a quantitative brittleness evaluation. In this article, the brittleness of X9’s cap rock has been evaluated by the five available effective methods that are based on mineral composition, elastic parameters, stress-strain curve, analytic hierarchy process, and fuzzy analytical hierarchy process, respectively, and the results of them are general, weak, weak, general, and general, respectively. Combined with the five evaluation results, a comprehensive brittleness evaluation based on geometric regular polygon method is proposed. The results show that the brittleness of X9’s cap rock is faint. Because of the comprehensive consideration of the limitations of existing brittleness evaluation methods, the excessive idealization of conventional regular polygon method, and the irrationality of division in evaluation grades, this method is improved based on the conventional regular polygon method and has advantages of comprehensive utility, strong feasibility, reliable result, and wide application range and can be used to evaluate similar targets.