Successful Cementing Based on New Design Methodology for Displacement of Non-Aqueous Drilling Fluid

Abstract Drilling fluid removal by spacer fluids is an important step in ensuring proper cementing and therefore adequate zonal isolation, especially when non-aqueous fluids (NAF) are used. In addition to the fluid mechanics aspect of displacement, a tensioactive package containing surfactant(s) and solvent(s) is typically added to the spacer base fluid to clean all surfaces, including the casing. However, current surfactants and solvents on the market have limited application in terms of temperature and type of drilling fluids. API and ISO standards recommend practices for evaluating the suitability of a spacer. The viscosity of NAF, spacer, and cement mixtures at various fixed ratios determines their rheological compatibility. The reverse-emulsion test or spacer-surfactant screening test (SSST) determines the percentage of spacer for inverting the NAF emulsion. Other non-standardized tests such as bottle tests or grid tests determine the efficiency of a surfactant/solvent aqueous solution to remove NAF from metallic or glass surfaces. But all these tests suffer from lack of reproducibility and limited automation. Improved alternative laboratory procedures have already been proposed. They include measuring rheology during SSST, which clearly shows the positive impact of early emulsion inversion on viscosity of NAF/spacer mixtures. In addition, proper preparation of metal surfaces clearly improves repeatability of the cleaning test, which now is performed with weighted spacer under temperature and pressure. Using these improved experimental methods, we performed more than 3,000 different tests on more than 200 tensioactive blends. Statistical analysis helped in selecting the optimum chemistry as a function of the conditions (type of base oil, salinity, and temperature). This allowed developing both guidelines and a tensioactive package comprising a limited number of chemicals (surfactants and solvents), from which the field user would select the ones to combine for the application. Only a few confirmation tests would be necessary at the location for planning a given cement operation. An advantage of developing a package of chemicals is ease of implementation at field level since it requires having only a few chemicals in inventory to cover all situations and limited local laboratory testing. The new methods have been successfully applied in several wells in which different types of nonaqueous fluids were used at various temperatures.