The mechanical properties of Lucaogou shale layered samples and the influence of minerals on fracture propagation

Abstract

Shale oil is one of the most promising alternative unconventional energies in the world, and Lucaogou Formation shows significant exploration potential, becoming the primary target in northwestern China. This paper compared the mechanical properties of shale layered samples from oil layer and interlayer of Lucaogou Formation, using uniaxial compressive tests with real-time micro-CT scanning. After that, the mineral analysis was conducted on one cross-section of the fractured sample to analyze the influence of mineral composition and distribution on micro-crack propagation. Such research has rarely been reported before. The results showed the surface porosity and elastic modulus of oil-bearing samples is larger than that of the interlayer samples, while the uniaxial compressive strength is lower. Besides, when there is only one dominant mineral with a content greater than 60%, a main crack tends to form at this area; When there are 2∼3 major minerals with a content of 10%–60%, a fractured zone with many fine micro-cracks is more likely to form here. Finally, the higher the Moh's hardness of the mineral, the more difficult it is for micro-cracks to develop through it.