Surfactant in Cement Slurry: Solution for the Problem of Incompatibility with Oil Based Mud

Abstract

Summary The main well cementing objective is to provide complete isolation of the formations behind the casing. To achieve this goal, the drilling fluid (mud) must be completely displaced in the annulus by cement. Effective mud removal is ensured by properly selected densities and fluid rheological hierarchy. However, even with ideal compliance with this rules, the oil based drilling fluid may not be completely replaced in the annulus. In such a case, contact of incompatible liquids occurs: cement and oil based mud. This leads to the formation of a viscous mass, which can cause high friction pressure during cementing job. In this situation, the zonal isolation of the formations is violated, and expensive remedial cementing job may be required. One solution for such cases may be use of surfactants to modify the properties of cementing systems in order to improve the compatibility of the drilling mud and cement slurry system. This paper presents the results of study describing the possibilities of using various surfactants and their effectiveness when used in cement slurries. The surfactant selection to obtain rheological compatibility of the oil based mud and cement slurry system is theoretically justified. The main attention was paid to rheological compatibility assessment and influence of surfactants on cement slurry properties, such as compressive strength development and thickening time. In addition to the initial assessment of the cement slurry properties, tests were carried out to determine cleaning and invert emulsion ability. In the process of studying, an express method for assessing the compatibility of cement and drilling mud was proposed and used. The work has shown that surfactant addition to cement slurry improves rheological compatibility between the cement and drilling fluid. The dependence of the rheological compatibility experiment results and type of surfactant is found. Technical and experimental confirmation of possibility of well cementing without the use of a spacer, was obtained. The novelty of the work is methodological approach for compatibility assessment of surfactant in cement slurry and slurry with drilling fluid (mud). This approach includes express method to select best surfactants candidates for further evaluation. The results of this study potentially allow to abandon the use of spacer in well cementing process and improve the quality of well cementing.