Study and application of circular micro-foam drilling fluid technology

During the exploration and development of low-pressured fractured buried hill reservoir and sandstone reservoir, serious lost circulation was encountered when using the conventional water based drilling fluid. High temperature tolerant circular micro-foam drilling fluid system was developed by Drill ing Tech. Research Inst. of Huabei Petroleum Administration. Laboratory evaluations were conducted on the dosage of foaming agent and foam stabilizer, and the stability, temperature tolerance, contamination resistance and reservoir protection of the drilling fluid. Testing results showed that the system has good foaming capability, large amount of fine micro-foam could be formed when the base fluid contacted with air; the foam has good stability, and the foam could keep stable in high temperature and long time circulation; the system also has high contamination resistance, and the formation fluid has good compatibility with drilling fluid additives. When batching the micro foam drilling fluid, the best adding amounts of foa-ming agent and foam stabilizer are 0. 4% - 1. 0% and 0. 1%-0. 3% respectively. Field using showed that the micro-foam drilling fluid has the characteristic of low density, and in drilling the third section, it kept stable and solved the problem of lost circulation when drilling the low-pressured reservoir, thus avoided formation damage and protected reservoir. The drilling fluid has good cuttings transportation with most of the cuttings returned to the surface, which totally met the engineering and geological needs of developing low-pressured oil and gas reservoir.