Prediction model of casing annulus pressure for deepwater well drilling and completion operation

Casing collapse and fracture may be caused by the rise of casing annulus temperature and pressure in the initial stage of production and testing of deepwater wells. Based on the casing program and wellbore heat transfer process, a pressure calculation model for casing annulus was established, which provides basis for annulus pressure control. With the annulus between testing string and production casing as an example, a casing annulus temperature calculation method was derived according to the principle of conservation of energy and wellbore heat transfer analysis. The casing annulus pressure prediction model was established for typical deepwater wells according to the volume change of casing annulus fluid with temperature and pressure, and in combination of the casing annulus PVT equation and annulus temperature equation. The casing annulus temperature and pressure calculation methods were successfully applied in the casing annulus temperature and pressure management operation in 7 deepwater wells in West Africa, and the predicted temperature and pressure were compared with the actual ones, which indicates that casing annulus temperature and pressure prediction methods have good accuracy, with the relative error below 10%.