Influence of petroleum on the failure pattern of saturated pre-cracked and intact sandstone

Abstract

Failures of the surrounding rock mass have been identified as the most serious threat to the stability of underground water-sealed petroleum storage depots. To elucidate the effects of petroleum on the deformation and failure patterns of sandstone, a series of uniaxial compression experiments have been conducted. The experimental results show that the strength of intact sandstone is enhanced with increasing immersion time in petroleum. However, for the pre-cracked specimen, the failure is strongly influenced by pre-existing flaws, and the fracturing degree is aggravated due to the immersion in petroleum, as stress concentration at a high level will form at the tips of a pre-existing flaw. Coupled with the lubrication action of petroleum between the fracture faces, cracks may initiate and propagate more readily. In addition, failures of splitting-shearing mixed mode, splitting mode and shearing mode take place corresponding to the three flaw angles (30°, 45°, 60°) involved in the experiment. Furthermore, for the flaw inclination of 45°, the failure mode transforms from splitting mode into splitting-shearing mixed mode when the arrangement of flaws is changed from rectangular to diamond. A discussion over experimental phenomenon is provided at the end of each section. The investigation provides further understanding of the failure mechanism of sandstone under the long term coupled influence of water and petroleum.