Preparation and Application of an Instant and Quick-Acting Suspending Agent for Well Cementing Prepad Fluids

Suspending agents presently used in prepad fluids for well cementing are mostly polymer/cellulose compounds. These suspending agents have a major advantage of high thickening ability; they can improve the suspending stability of a prepad fluid, thereby ensuring the safety of well cementing operation. These kinds of suspending agents, on the other hand, generally swell very slowly in water (> 3 h), and are therefore unable to quickly thicken and prepad fluid to improve its suspending stability. Researches have been conducted in an effort to develop a new suspending agent for well cementing prepad fluids. By optimizing the formulae of suspending agents, an instant and quick acting suspending fluid with superior properties has been developed. This suspending agent fluid has low viscosity and low gel strength. Laboratory experimental results show that after being dissolved in water for 3 min, the suspending agent swells completely and the suspending property of the fluid is greatly improved, meaning that the suspending agent has high quick-acting ability. The funnel viscosity of the suspending agent fluid is about 42 sec, meaning that the suspending agent is convenient to use. A prepad fluid formulated with 4%−5% of this suspending agent as the core additive has been used in cementing a well drilled with water-based drilling fluids or oil-based drilling fluids, the suspending agent functioned normally at temperatures of 200℃ or higher. The density difference between the upper part and the lower part of the prepad fluid was less than 0.03 g/cm³, indicating that the prepad fluid had excellent stability. The field operation using the prepad fluid was conducted smoothly and the job quality of the well cementing operation was outstanding, meaning that this prepad fluid formulated with the newly developed suspending agent is able to enhance the displacing efficiency of cement slurries and has higher promotion value.