Shallow Water Drilling Operations Using DP Rig: A Case Study on the Pre-Salt of Campos Basin

The target well location of this study has unique characteristics that pose a significant challenge to its construction: a water depth (WD) of less than 300 meters, high temperature, and the need for heavier fluid to drill through the salt with high burial. Due to restrictions in alternative locations, a technical feasibility study was conducted to evaluate the possibility of constructing this well using a dynamically positioned rig. For this study, several simulations were performed using a riser analysis software, allowing a sensitivity analysis regarding the most impactful variables for this operation: wellhead load capacity, water depth variations, Emergency Disconnection Sequence (EDS) time, environmental conditions, soil parameters, among others. From these studies, it was found that considering typical and collinear environmental conditions leads to very restrictive operational limits. An ideal scenario for using a real-time riser analysis system, which determines operational limits based on measured conditions at the location, usually leading to more flexible operational limits. However, using a real-time riser analysis system can occasionally result in restrictive operational limits, which may even result in a preventive disconnection to avoid unsafe situations where there is not enough time to perform an emergency disconnection in a drift-off scenario and avoid damage to the riser and/or the well. Estimating an expected number of these disconnections is crucial information for a technical-economic feasibility assessment of the operation. Based on historical metocean data from the region, a predictive riser analysis methodology was implemented to estimate Non-Productive Time (NPT) associated with stoppages and preventive disconnections due to adverse conditions. This analysis allows for more precise operation planning and the estimation of typical limits expected from real-time analysis, resulting in significant operational cost reduction and better risk management. Additionally, a decision flowchart was developed for scenarios where the red watch circle resulting from real-time riser analysis becomes critical. This system establishes clear parameters and sequential preventive actions that the operational team must take to safeguard the integrity of the wellhead equipment and the rig, avoiding damage and reducing the risk of incidents. With the obtained results, the operation with a DP rig in shallow water (285 m) proved viable with the adoption of real-time riser analysis, along with a robust risk analysis mapping operations with high criticality and specific actions for the scenario, as well as well design considerations that enable the operation under these conditions.