Abstract: The western parts of the Yanchang Oilfield contain layers with a high tendency toward lost circulation.Frequent lost circulations of cement slurry during cementation can lead to poor quality in cementation.Under such circumstances,technical challenges in the cementation of horizontal wells in the area had been studied to develop cementation technologies suitable for low-pressure formations susceptible to lost circulation in the western parts of the Yanchang Oilfield.These technologies involved deployment of composite low-density cement slurries,plugging pre-pad fluids with desirable formulations,casing centralizer of suitable type,optimization of installation positions of casing centralizers and technologies with satisfactory displacement efficiencies.The newly developed composite low-density cement slurry had outstanding overall performances with API filtration rates below 50 mL,low-temperature 48 h compress strength of cement stone over 12 MPa,outstanding settlement stability with density differences below 0.03 kg/L.By adding composite fiber plugging materials,the pre-pad fluids could effectively seal off formations susceptible to lost circulation and enhance the bearing capacities of the formation.The cementation technology was deployed in over 10 wells in western parts of the Yanchang Oilfield with success rate of 100%,with a high-quality cementation rate of 90% and lost circulation rate of 3%.Research results showed the newly developed cementation technology for the low-pressure formations susceptible to lost circulation could effectively eliminate lost circulation in cementation operations in western parts of the Yanchang Oilfield.Eventually,the quality of cementation operations could be enhanced dramatically.