| A new class of emulsifying agents that form reversible oil-in-water emulsions are synthesized. The emulsifying agent can be triggered by changes in the pH. The synthesis procedure and the effect of varying the hydrophobic monomer concentration, chain transfer agent concentration and initiator type are investigated. The emulsifier is characterized by drop coalescence, emulsion stability and interfacial tension measurements. The emulsification properties of this new emulsifying agent were found to be excellent and very pH sensitive at pH values below 3.; Experimental results indicated that the emulsified completion fluids reduced fluid loss to the formation compared to fluids with no emulsified oil. The filtrate volume for the emulsion fluids tested compares favorably with other completion fluids but is large compared to conventional drilling muds because of the absence of other filtration control agents, such as, bio-polymers and starch. The permeability of the core, injection pressure, temperature, percent oil, viscosity of the continuous phase, solid particles present, and droplet size all play important roles in determining the filtration properties of the completion fluids. Overbalance pressure has a major effect on the filtration properties of the emulsion.; Long core experiments (6 inch cores) showed deep invasion of the emulsion droplets into the core in the absence of CaCO3 particles in the completion fluid. Excellent return permeabilities (∼100%) were obtained with fluids containing CaCO3 particles.; Outmans model for static filtration of compressible filter-cakes was used to calculate the filtrate volume versus time. The experimental results were not in agreement with this classical filtration theory. This indicates that emulsion droplets and solids are invading the formation while the external filter-cake is mainly composed of the solid particles.; Models provided by Sherwood and Zydney et al. were used to calculate the permeability of a bed of deformable droplets. These models suggest ultra-low permeability at high filtration pressures due to deformation of the droplets. This was not observed in our experiments. In fact measured filter-cake permeabilities were estimated to be in the range of 0.1 md which is several orders of magnitude larger than those estimated by using models for emulsion filter cakes. (Abstract shortened by UMI.)... |
