The application of safe-guards, safety triggers and automated procedures to control the mud-pumps, hoisting system and top-drive allows for safer, more consistent and more efficient drilling operations. Attempting to apply drilling automation on a floater needs to manage the impact of the unpredictable movement of the drill-string induced by heave movements.
Because of the drill-string elasticity and the continuous movement of the rig, it is challenging to estimate the bit position, the bottom hole depth or the instantaneous rate of penetration. Yet, these estimations are crucial for the evaluation of cuttings production and their transport, or dynamic open hole pressures. Furthermore, the variability of the top of string movement can change abruptly when heave compensation is turned on or off or depending on the efficiency of the heave compensation system. These facts have an impact on the look-ahead strategy to determine safe drilling parameters.
An existing drilling automation system, originally designed for fixed platforms, has been modified to meet those new requirements. For this first adaptation, only vertical drilling has been considered. Heave movements with and without compensation are constantly monitored so that sudden or slow changes in amplitudes get accounted for. Induced effects on downhole pressures are estimated via hydraulic simulations for a wide range of drilling and heave scenarios. Consequently, the design of the automation system had to be deeply modified to incorporate this additional dimension. The resulting system has been used for the drilling of three exploration wells, in eleven sections.
Offshore drilling operations are characterized by a large variability of the drilling operation conditions. On a floater, the drilling context is even more challenging as it is subject to ever changing weather conditions. Yet, by utilizing model-based drilling automation solutions it is possible to improve drilling efficiency.