Abstract: As the features of volcanic formations in Songnan Area are strong abrasion,high compressive strength,rich fractures and faults,the drilling of horizontal wells in these formation is likely to encounter the loss of circulation,collapse,low rate of penetration(ROP),which leads to long drilling cycle time.To improve ROP,shorten drilling time and cut the cost of horizontal wells in this area,based on maximum drillability value of formation,three pressure profiles and nodal analysis methods,KS1952SGR high efficiency PDC drilling bit was selected and optimized the 3-stage casing program in slim holes(the hole size of 152.4 mm in the third spuding stage),the well trajectory including vertical,build-up,stabilizing and horizontal sections,proper displacement from landing point to first target point as well as composite drilling technology were optimized by using software modeling.The application of these techniques in 5 wells in Songnan Area showed the average rate of penetration increased by 23.9%,and the average drilling time reduced by 25.2%.