Effect of the Sodium and Potassium Chloride on the Mechanical and Plastic Properties on the Oil Well Cement Slurries

Abstract

In recent times, a large reserve of oil and gas in a Pre-Salt zone has been identified in Brazil. In this reserve it is necessary to drill and cement a layer of approximately 2.000 meters of salt rock. In salt rocks, the contact of cement with the rock during the cementing operation can cause the dissolution of the rock and salt can migrate to the cement slurry. Cementitious systems containing salt in their composition have been proposed to minimize the transport of rock salt to the slurry. Considering that the presence of salt can cause changes in the properties of the slurry and compromises the cementing quality. Studies are necessary to understand how the type and concentration of salt can affect the short and long term behavior of the slurry. In this work, the effect of the amount of sodium chloride (NaCl) and potassium chloride (KCl) on the properties of the oil well cement slurry was studied. For this, slurries containing 5%, 10%, 12.5%, 15%, 17.5%, 20% and 36% NaCl by the weight of water (BWOW), and 1%, 3%, 5%, 7%, 10% and 34% KCl (BWOW) were designed. The effect of salt type and content on the rheology, free-fluid and mechanical properties such as compression strength, Young’s modulus, Poisson’s rate and splitting tension strength was investigated. The mechanical properties were evaluated at an age of 8 hours of curing in water at 38°C (100° F) and 60° C (140° F) and 7 days of curing in water at 60° C. The addition of NaCl and KCl resulted in similar behavior in almost all the properties studied. The properties of freshly and early-age, as free-fluid and compression strength, of saline slurry differed in two different mechanisms depending by the salt concentration. For other side, in most cases, the rheological and long-age properties were reduced with an increase in salt content.