Abstract: In order to increase the gas drainage area,comprehend the natural gas production of He 3 formation,implement horizontal drilling technology experiments in DP3 well in Da- niudi gas field,horizontal section in DP3 well adopt water- based underbalanced drilling for effectively protecting gas formation,using clay-free & drift pearl of the drilling and completion fluid system as recirculated medium,the system is characterized by using light weight additive-glass beads declining drilling density to achieve underbalanced drilling and effectively protect reservoirs.Field application showed that clay-free & drift pearl of the drilling and completion fluid system meeting safe production requirements,imple- ment the balanced drilling technology,have realization of mi cro-underbalanced drilling in part section,and effectively protect the reservoir.Solve well of the horizontal wells with debris,solid control,lubrication,wellbore stability,the protection of reservoirs,and other technical problems.The unimpeded flow of later test was 6.34×10~4 m~3/d.