Abstract:

In order to evaluate the fracability of the Lower Cambrian Niutitang Formation (Fm.) shale reservoir in northwestern (NW) Hunan, we took the well HY1 as the research target.Through intensive core sampling, experimental analysis, integrated logging interpretation and other methods, the characteristics of organic carbon content, reservoir physical property, fracture characteristics, brittle mineral compositions, and rock mechanic properties were systematically analyzed, and the shale reservoir fracability further discussed. The results show that the Niutitang Formation in well HY1 is featured by high organic carbon content (0.25% to 13.3%, average 2.91%), and the organic-rich shale developed in the lower Niutitang Formation is 65 m thick. Fractures are less developed in organic-rich shale with the low density (0.27 to 1.21pieces/m), but shale-bedding fractures are developed. The Niutitang Fm. shale is also featured by high mineral brittleness index (17.7% to 86.4%), high static Young’s modulus (37 to 62 GPa), low static Poisson’s ratio (0.14 to 0.26), and high two-phase horizontal pressure difference coefficient (0.21 to 0.54). Overall, the Niutitang Fm. shale reservoir is favorable for fracturing with high brittleness and rock strength, yet the existence of a large number of shale bedding fractures increases the fracture complexity, and give certain negative impact on fracture generation. The double wing fracture is easy to form due to the high two-phase horizontal pressure difference. Therefore, the leakage caused by shale bedding fractures and the influence on fracture height and length extension should be considered comprehensively in fracturing design.

Key words: northwestern Hunan, well HY1, Niutitang Formation, shale reservoir, fracability