Abstract: With the development of oil and gas exploration in the Xihu Sag to deep layers, the drilling depth continues to increase. Under the existing casing layers, it is necessary to increase the surface drilling depth to relieve the drilling pressure of the lower layers. With the poor rock drill-ability of the surface drilling, the low mechanical drilling speed, the long drilling cycle, and the difficulty to determine the maximum safe-drilling depth of the surface opening, the surface opening fast drilling technology was limited. To solve the problems, by analyzing the formation pressure characteristics and collapse periods, the determination method of the maximum drilling depth to maintain the stability of the formation and the safety of the open hole was determined; by optimizing the drilling tool assembly, drilling fluid technology and drilling parameters, the mechanical drilling speed of the formation under the surface drilling was increased, and finally a set of surface-opening fast drilling techniques suitable for Xihu Sag have been formed. Field practice shows that this set of technologies has achieved a breakthrough in the maximum safe drilling depth of the surface drilling in the Xihu Sag, effectively increasing the mechanical drilling speed of the lower surface drilling with good promotion value.