CLEANING EFFICIENCY EVALUATION OF MUD CAKE ADSORBED ON THE WELLBORE DURING THE CEMENTING PROCESS UNDER HIGH-TEMPERATURE CONDITIONS

To improve the cleaning efficiency during the cementing process in high-temperature and highpressure (HTHP) gas wells, a set of cleaning efficiency evaluation devices for flushing fluids was developed. Based on the downhole HTHP conditions of the LD10-1 block in the western South China Sea, the influence of the annulus flow rate and flushing time of the flushing fluid on the cleaning efficiency was investigated by the evaluation device and numerical simulation method. The dosage of the key treatment agent W21L was optimized. The results show that the experimental method can well simulate the actual temperature and pressure difference conditions in the downhole, and the experimental repeatability is strong. Under the condition of constant flushing time and speed, the cleaning efficiency increases with increasing experimental temperature. When the flushing time is set to 15 minutes, the cleaning efficiency can reach 88.4% when the annulus flow rate is greater than 1.34 m/s and 76.8% when the flushing time is more than 25 minutes for a flushing speed of 0.75 m/s. For the cleaning agent W21L, the cleaning efficiency can reach 82.1% when the dosage is greater than 9%. The research results provide support for determining cementing process parameters to improve the cementing quality in the LD10-1 block.