Addressing the Challenges of Drilling in Shallow Water with Modern Floaters

A growing challenge encountered by subsea drilling contractors is to drill wells in shallow water environments using modern dynamically positioned floaters that are designed to drill in water depths greater than 3,050 meters or 10,000 feet. There are many challenges related to drilling in shallow water environments, i.e. not exceeding a depth of 305 meters or 1,000 feet. These hurdles are notably the possible loss of position, the limits of the drilling riser, subsea wellhead and structural casing when there is a black-out or when the floater is moving off location. The objective of this paper is to present a methodology for creating an overall decision tree that can be easily readable and usable by the rig crew and engineering support to understand how to get to the next operation while remaining within the design limits of the drilling riser, subsea wellhead and structural casing strings. In addition, the workflow can help determine at which point the emergency disconnect sequence (EDS) should be launched when there is a black-out and the vessel is moving off location. Furthermore, the flow diagram can tell what should be done when the vessel is blown off, cannot hold location. Finally, the process diagram shows what decision should be made when harsh metocean conditions are forecasted while conducting drilling operations in a ‘safe’ dynamically positioned spot. The results of this study conducted for a well located in the Campos basin offshore Brazil are a complete procedure combining multiple decision trees that can advise, while conducting well operations in a shallow water environment, depending upon predefined risk levels (low, medium and high) and weather forecast, whether one should wait on weather, or proceed with shallow water operations, or optimize the drilling riser and well model. Then, if the vessel experiences a black-out or the floater is pushed off the well location, unable to hold its position over the well, real-time decisions can be made as a function of time and/or distance relative to the red arc and point of disconnect. As a result, either the red arc position is monitored, or an emergency disconnect sequence can be launched or normal operations can resume. The originality of the overall procedure is that it can be used in real time while drilling in shallow water with a modern vessel and can be easily readable and usable by the drilling crew, the dynamic positioning operator and the drilling contractor engineering team.