延长油田西部地区低压易漏地层固井技术

延长油田西部地区存在漏失层，固井过程中水泥浆易发生漏失失返，导致固井质量较差。为此，在分析该地区水平井固井技术难点的基础上，优选复合粉煤灰低密度水泥浆、堵漏前置液配方和套管扶正器类型，优化套管扶正器安放位置，制定提高顶替效率的技术措施，形成了适用于延长油田西部地区的低压易漏地层固井技术。室内试验结果表明:复合粉煤灰低密度水泥浆综合性能良好，API滤失量小于50 mL，在低温下水泥石48 h抗压强度达到12 MPa以上，沉降稳定性好，上下密度差小于0.03 kg/L；前置液加入复合纤维封堵材料能封堵易漏层，提高其承压能力。低压易漏地层固井技术在延长油田西部地区已应用10余井次，固井成功率100%，固井质量合格率达90%，漏失率降至3%。研究表明，低压易漏地层固井技术能解决延长油田西部地区固井中存在的漏失问题，达到提高固井质量的目的。 

Cementation Technology for Low-Pressure Formations Susceptible to Lost Circulation in Western Area of the Yanchang Oilfield

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.