The effect of nano-silica in oil-well cement

Abstract

A goal for all drilling operations is that they are performed within satisfactory safety- and financial boundaries. A big part of this is that the cementing operations are performed in a best possible manner, and having a good quality cement contributes in that regard. This thesis has explored the effects of using nano-silica as an additive to see how it affects the cement properties. The method to investigate this has been experimental. The focus of the experiments has been on parameters affecting the possibility of gas migration in the annulus. Gas migration was in 2005 responsible for 25 percent of the failures in primary cementing jobs. More specifically, elasticity and shrinkage were the parameters that were investigated. The elasticity tests have been performed for two, seven and fourteen days cure time at various mixtures. The shrinkage experiments measured shrinkage for 24 hours of cure time. The testing should optimally have been performed under in-situ well conditions, but as this was not possible it was emphasized that all the tests were conducted under the same conditions to get comparable results. In total, 72 samples has been made and tested for the elasticity tests. These were divided between 11 different cement mixtures. For the shrinkage experiment time limitations made it not possible to get test results for all cement mixtures. In total, six of the mixtures were tested for shrinkage.The results have indicated that the addition of nano-silica affects the cement properties. Most noticeable has been alteration of the viscosity of the cement slurry and early strength development. However, after fourteen days cure time the testing showed that the neat cement had improved significantly in quality, and was now giving among the best test results. For the shrinkage experiment the results suggested that nano-silica addition did not give favorable cement properties. Summarized, no nano-silica cement mixture proved favorable compared to the neat cement based on results from all the experiments.