Mud-Cake Displacement Agents for Moderate to Low Temperature Conditions

During cementing operations in medium- and low-temperature oil and gas wells, mud cakes formed by water-based drilling fluids with strong viscosity, shear force, and high adsorption capacity exhibit dense structures and strong adhesion. Existing flushing agents generally suffer from insufficient penetration, low flushing efficiency, and poor adaptability to low temperatures, which easily lead to poor cementing quality at the second interface and engineering hazards such as annular channeling. To address these problems, based on the core principles of penetration, chelation, deflocculation, wetting, and wedge splitting, a multi-component synergistic system comprising FC-1, PA-2, diethylene glycol butyl ether, and phosphates was constructed through formulation optimization. Consequently, a novel flushing agent S-2 capable of rapidly removing mud cakes with high flushing efficiency under medium- and low-temperature conditions was developed. The comprehensive performance of S-2 was systematically characterized through laboratory evaluations and field tests. The results indicated the followings: (1) S-2 exhibited excellent compatibility and met the operational requirements for various types of water-based drilling fluids, including polymer, polysulfonate, and potassium-based drilling fluids. (2) Within the medium- and low-temperature range from room temperature to 80 °C, S-2 achieved a mud cake removal rate of over 90% within 5–10 min. Compared with commercially available flushing agents, it exhibited a flushing efficiency increased by more than 190%, demonstrating outstanding rapid stripping capability against mud cakes with strong viscosity, shear force, and high adsorption capacity. (3) S-2 had a low pour point of −18 °C and maintained good fluidity at −10 °C, meeting transportation and storage requirements in low-temperature environments. (4) S-2 showed excellent compatibility with both drilling fluids and cement slurries, effectively improving the cementing quality at the second interface. This flushing agent was successfully applied in the Φ244.5 mm production casing cementing operation of Well xxx in the Bohai Oilfield. The cementing quality was evaluated as excellent. It demonstrated a favorable application effect and provided new technical support for high-quality cementing in medium- and low-temperature oil and gas wells.