Evaluation of Strength Properties of Cement Containing NaCl in Mixing Water for Cementing Wells in Halite Strata

Cementing wells in salt rock is a challenging operation, particularly due to changes in cement properties as a result of interaction with dissolved rock, which can lead to poor cementing quality and risks associated with leakage. In this paper, the effects of NaCl content on the properties of the cement in contact with selected salt rock samples are investigated. The results are suitable for determining the dependencies of cement properties required for the selection of a plugging system formulation suitable for the geological and technical target conditions in well construction. The cement samples were exposed to aqueous NaCl solutions for 28 days after which no significant changes in mechanical properties, such as compressive strength, gas permeability coefficient, expansion/shrinkage and contact strength with the salt rock, were observed. Based on the results, the optimum strength properties of the cement were determined at a saturation coefficient (Kn) between 0.6 and 0.8 where up to 21% increase in the compressive strength was identified possibly due to the formation of strong bondings between the cement and the salt rock. In addition, the growth of salt crystals inside the cement at high concentrations of NaCl was determined through increasing linear dimensions of the cement sample by 2.5% that leads to the formation of microcracks and channels as confirmed by the obtained results of gas permeability tests, namely an increase from 0.38 to 0.91 mD.