The Development and Application of Well Cementing Cleaning Agent DQQX-2 and Flushing Fluid Formulated with It

Residual oil based drilling fluids retained on the surfaces of casing strings and on the borehole walls become gels that are difficult to wash away, hence affecting the job quality of well cementing. To solve this problem, efforts were made on the development of flushing fluids for well cementing. By studying the physical properties of various cleaning agents for use in well cementing, a cleaning agent system with high cleaning performance and suspending capacity is developed. Based on the technical requirements for the well cementing pre-pad fluids, the suspending agent and other additives for a high efficiency flushing fluid are engineered. Laboratory study shows that in the flushing fluid when the concentration of the cleaning agent is in a range of 3% to 6% and the concentration of the suspending agent is 3%, the flushing fluid can function normally at 180 ℃, the density of the flushing fluid can be adjusted between 1.2 g/cm³ and 2.0 g/cm³, and the difference between the density of the top fluid and the density of the bottom fluid is less than 0.03 g/cm³ after the flushing fluid stands for 24 h at 23 ℃. The time for the flushing fluid to clean completely the residual oil-based drilling fluids is within 7 min. This flushing fluid has good compatibility with the drilling fluids and the cement slurries. Field operation results show that in wells cleaned with this flushing fluid, the cementing job is performed smoothly, and the excellent job quality of cementing the horizontal section of a well is more than 93% of the total. Field operation achievements prove that this flushing fluid can be used to better clean the wellbores drilled with oil-based drilling fluids and enhance the efficiency of displacing the cement slurries, thereby improving the job quality of well cementing.