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.