Well Control and Temperature Modelling Facilitates the Effective Delivery of Challenging Shallow Water HPHT Exploration Well

Abstract

Drilling operations in high-pressure/high-temperature (HP/HT) environments can be very challenging and costly. In an exploration well being drilled in a unique depositional environment, a rapid increase in pore pressure was anticipated, potentially reaching HP/HT conditions of up to 12,000 psi and over 180°C. The absence of close offset wells resulted in a large uncertainty in the magnitude of the pore pressure. This drove the planned casing design, which was limited by kick tolerance and potentially narrow margins between pore pressure and fracture gradient, resulting in planning for up to six casing strings. To respond to this challenge, standard engineering practices were augmented with additional monitoring and predictive modelling solutions to improve well control and to predict and explain complex well behaviour and mitigate the associated drilling risks. The models were calibrated with measured mud properties and wellbore temperatures and pressures during operations. They were then used to simulate, explain, and predict variations in downhole pressures and surface mud volumes. Various innovative applications were used to guide safe operational decision-making. Where conventional practices would not have allowed, this modelling enabled total depth of the well to be reached while incurring minimal nonproductive time and no well control incidents. By understanding wellbore conditions using advanced well control and temperature simulators, abnormalities normally failing the conventional practices could be detected and explained. This improved well control, safety, rig performance, and effective application of resources.