The global demand onto large volumes of hydrocarbons to be stored in rock caverns lead to the development of very large caverns. The larger the cavern sections, the larger the potentially unstable blocks and the risk of megawedges.

The hydrodynamic containment of hydrocarbons in mined hard-rock caverns requires the presence of a water curtain system approximately 20 m above the storage galleries such as to obtain a permanent convergent flow of water in the caverns. A good understanding of the effects of the distribution of the water pore pressure in the different joint sets as a function of their hydraulic conductivity, mechanical properties and geometry is necessary for evaluation of the stability of the fractured rock mass.

The stability and tightness of a hydrocarbon storage cavern in a fractured rock mass have been modelled using DISROC® finite element code developed for the hydromechanical analysis of two-dimensional discontinuous media. This hydromechanical fully coupled model takes into account the effect of rock joint aperture variation on the hydraulic conductivity of rock joints based on a cubic law.

A Mohr-Coulomb safety factor has been calculated for different wedges during cavern excavation. The threshold for the cavern leakage pressure has been assessed during hydrocarbon operation condition. The hydro-mechanical modelling results reveal no significant impact on the cavern integrity comparing to non-coupled mechanical and hydrogeological models.

1 Introduction

The stability of underground excavations in jointed rock mass has been largely studied using continuous medium modelling approaches.

Usmani A. et al. (2018) compared continuum and discontinuum analysis of stability of a storage rock cavern. Their results indicate that inclusion of discontinuities in rock mass for numerical modelling captures essential instability mechanisms around the cavern while continuum modelling underestimates the cavern deformations and displacements.

The evaluation of hydraulic conductivity of fractured rock mass is usually addressed based on an equivalent continuum media using semi-analytical (Xu Z. et al; 2015) or numerical approaches (Goldschneider A. and Amantini E.; 2009). Some authors developed a discontinuum model to simulate the groundwater flow in fractured rocks (Karay G. and Hajnal G.; 2015).

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