Mechanical properties of EVA-modified cement for underground gas storage

Abstract

Underground gas storage (UGS) is an artificial gas reservoir used for balancing the supply-demand chain throughout the year. During its operation cycle, the cement sheath experiences cyclic mechanical stress, and thermal and may crack due to its low elasticity, hard brittleness, and porosity. These cracks could lead to the transmission of stored gas through the cement behind the casing and before the formation and can even be a source of micro-cracks. Therefore, the mechanical properties of the cement sheath have higher requirements. In this work, a new material was used to prevent cement cracking, improve cement elasticity at low stress and deformability at high stress, reduce the number of pores and reduce the crack propagation in the cement used for completion of UGS wells. The experimental results showed that mixing EVA into cement decreases the compressive strength, but significantly improves the toughness and deformability at high stress and the elasticity deformation restorability at low stress. Moreover, the addition of EVA results in the remarkable reduces reduction of macropores.