رضا آذین

In order to shave the peak demands during the cold seasons, underground gas storage (UGS), balancing the supply-demand chain throughout the year, has been accepted as a strategic method. During the successive UGS cycles, the well cement experiences cyclic mechanical, thermal, and hydraulic stress and may crack due to its low elasticity and ductility. This could lead to the transmission of stored gas through cementing behind casing, one of the major challenges experienced in UGS operations, so posing high workover costs on UGS wells. In addition to workover costs, the loss of inventory due to gas transmission makes the reservoir insufficient in proper gas supply during the high-demand season. In this work, a new formulation has been invented in order to prevent cement cracking, improve cement elasticity and ductility, and reduce the crack propagation in the cement used for completion of UGS well. The new formulation adds a polymer and an elastomer to cement composition. Results showed that addition of latex to cement decreases the density, hydration and fluid loss of cement; also, the rate of cement bonding decreases. On the other hand, addition of polypropylene fibers results in dramatic improvement of compressive strength and stress strain properties of the cement. In comparison with elastomer, this additive provides a higher threshold elasticity of cement. Also, the combined cohesive effect of latex and flexibility of microfibers brings about the best resistance against excessive pressures.