Optimized, safe and fast drilling technologies used in the ultra deep and high temperature wells in Yangshuiwu buried hill

In the drilling process of oil and gas wells in the ultra deep and ultra high temperature buried hill of buried-hill structural belt in Langgu sag of central Hebei, several problems are encountered, including leakage, blowout, sticking, low rate of penetration (ROP) and difficult trajectory control. In order to solve these problems, this paper firstly analyzed the drilling difficulties of drilled wells and investigated domestic ROP improvement technologies of ultra deep wells. Then, a series of measures were taken. For example, the casing program was optimized and the well track was simplified. Based on the stratigraphic characteristics, impregnated-tooth PDC bit was designed, and bottom hole assembly (BHA) and drilling parameters were optimized. In addition, low solid and high temperature (220 ℃) drilling fluid was prepared, and 200 ℃ all-metal downhole pulser for measurement while drilling was developed. The field application results show that the optimized casing program and well track are convenient for the adjustment of wellbore trajectory. Owing to the application of efficient PDC bit, combined with the supporting ROP improvement and rock breaking tools, the average ROP is increased by 1-2 times. The performance of low solid and high temperature drilling fluid is stable under the temperature of 200 ℃, which can meet the requirements of safe construction. The all-metal downhole pulser for measurement while drilling can work continuously for over 200 h under the well temperature of 175 ℃. The average drilling cycle is 50% shorter than that in the early stage, the maximum total well depth is 6 455 m and the measured bottom hole static temperature is 207 ℃ in this block. In conclusion, the optimized, safe and fast drilling technologies adopted here can provide references for the drilling of ultra deep and ultra high temperature wells in the late stage.