Abstract
Unwary axial and rotational movement of the drill-string can cause formation fracturing or fluid influx resulting in costly remedial actions. With increasingly complex wellbore geometries and narrow geo-pressure windows, it is not always obvious for the Driller to estimate the real manoeuvring limits of the drawworks and the topdrive, especially under poor downhole conditions. The solution presented in this paper uses continuously updated safe guards applied to the drilling control system to maintain a downhole pressure within the acceptable limits of the open hole formations. It also stops automatically the movement of the drill-string in case of abnormal hook loads or surface torques. Since automatic actions can be triggered in case of an unexpected situation, some standard procedures have been fully automated, including friction tests and back-reaming.
Numerical models are used to constantly calculate the maximum accelerations and velocities which can be applied to the drill-string in the current drilling conditions. The resulting envelope of protection is depending on many factors. Therefore, a proper evaluation of the downhole conditions is of paramount importance for the quality of the calculated safe guards. An automatic calibration of the physical models, based on surface measurements, is at the heart of the system. The calibrated mechanical models are used to determine the limits for abnormal surface torques or hook loads. It is therefore possible to automatically take actions in case of overpull, set-down weight or high torque.
In 2008, a preliminary version of the system has been tested during the drilling of a well in the North Sea. Even though the control algorithms did work well at that time, it has been noticed that in some circumstances the drilling control system would not be ready in time for fast changing drilling conditions. An improved version of the drawworks and topdrive automation system has been tested during the drilling of three North Sea wells in the spring of 2009. In this last version, the response time of the system has been optimal at all time. The Drillers involved in the testing of the system have found the system useful and user-friendly.
