Temperature Risk At BOP Rams: New Insights from Well Modelling

Abstract The MOHO Bilondo field is located 72 km offshore Republic of Congo at 440 to 1180 m of water depth. It is operated by TotalEnergies with partners Chevron and SNPC. The drilling assessment of an exploration well revealed a high temperature risk of overheating of the Blow-Out Preventer (BOP) rams elastomers. This study introduces a novel modelling approach to address this risk, while also highlighting the potential for hydrate formation within the production tubing below the mud line. To estimate the temperature risk for the Blow-Out Preventer (BOP) rams, Transient Well Flow Modelling (TWFM) was used, incorporating the well, the BOP and the marine riser. The BOP was positioned at the well head, forming a continuous block of 10m height. Within the BOP, rams were discretized to capture the radial temperature distribution. This approach enabled the prediction of temperature evolution during clean-up and restart of the well. Sensitivity analyses were also performed to address the impact of both reservoir fluid and reservoir temperature. This paper outlines the importance of transient flow modelling to address temperature issues and thereby reduce operational risks. A high-resolution modelling of the well and the BOP was key to predict the temperature evolution during the drilling stem test (DST) sequence, for both hydrates risk assessment within the well during transient flow, and integrity of rams during steady-state conditions. The sensitivities highlighted that despite the high reservoir temperature, there is always a risk of hydrate formation within the well when it flows below a given liquid rate threshold. In addition, it was possible to provide a maximum production rate to limit the temperature at the BOP rams and preserve their integrity during the DST sequences. Our innovative modelling approach enables the prediction of the liquid rate threshold necessary to sustain BOP ram integrity. This study also demonstrates that in deep offshore, there is always a need for hydrate risk assessment despite higher reservoir temperature, particularly for low liquid rates in transient flow conditions.