顺北二叠系低压易漏井固井质量影响因素探讨

顺北油田二叠系地层孔隙裂缝发育，漏失压力低，完钻井固井漏失率为82%，井口反挤补救固井54.5%，导致固井质量不理想；为此，以该区域已施工井为参考依据，分别以地层承压能力识别方法、套管居中度评价方法、冲洗液紊流冲洗效果评价及井筒浆体匹配性计算为研究对象，系统分析了区域固井质量的内因。研究成果表明，二叠系地层漏失压力为62~67 MPa；在井径扩大率小于10%、井斜角低于0.3°时，扶正器间距可为55 m，而井眼质量较差时建议间距为22 m；前置液黏度偏高、隔离液与领浆性能参数不匹配导致前置液滞留井内，以及水泥浆提前返出井口，固井质量不理想。该研究成果为低压易漏地层漏失压降计算、扶正器安放间距设计及井筒浆体性能优化提供了系统研究的新思路，为解决该类固井难题提供了关键技术措施。 

Investigation of Factors Affecting Cementing Job Quality in Wells Penetrating Low Pressure Permian Formations Having Mud Loss Tendency in Shunbei Oilfield

The Permian System formation in Shunbei oilfield is developed with fractures and has low leaking pressures, resulting in 82% of the wells experiencing lost circulation during well cementing and 54.5% of the wells had to be re-cemented through reverse squeezing of cement slurry. Cementing job quality has been unsatisfactory in the past. The internal causes affecting the quality of well cementing in the area was systematically analyzed using the methods such as identification of pressure bearing capacity of the formation, evaluation of the eccentricity of casing string, performance evaluation of a flushing fluid at turbulent flow and calculation of the compatibility between different slurries. It was found that the leaking pressure of the Permian System formation is between 62 MPa and 67 MPa. Distance between two centralizers can be 55 m when the percent hole enlargement is 10% and hole angle less than 0.3°. This distance is reduced to 22 m when the quality of the borehole is poor. Poor well cementing generally results because of high viscosity of prepad fluid, incompatibility between the parameters of spacer and lead slurry which results in retention of spacer in the hole, as well as cementing slurry returning to the surface ahead of time. This study has provided a new clue for calculating the leaking pressure of a formation with low pressure during cementing, designing the placement of centralizers and optimizing cement slurries, and presented a key technical measure to the similar well cementing problems.