Managed wellhead backpressure during waiting setting of managed pressure cementing

Abstract

Managed pressure cementing (MPC) has been successfully used to reduce risk lost circulation and improve cementing quality in wells with a narrow safe pressure window. However, during the waiting setting period of MPC, the magnitude of the managed well backpressure is still based on experience, which results in a high risk of leakage or gas channeling especially in formations with a narrow safe density window. Therefore, a backpressure managing method is proposed here based on a model we built for calculating wellhead backpressure. This model was used to analyze the effect of cement slurry, temperature and wellbore pressure on wellhead backpressure. The results show that hydration, filtration shrinkage and gel supporting are essential to reduce wellbore pressure, although hydration is less effective compared with the latter two on pressure reduction. The magnitude and duration of wellhead backpressure depend on the extent of volume shrinkage and the gel strength development of cement slurry. Latex-cement slurry requires minimal wellhead backpressure with the shortest duration. Temperature and wellbore pressure greatly impact wellhead backpressure with temperature playing a more dominant role.