Pushing the boundaries of oil and gas exploration and development to new frontiers have led to exposure and more significant uncertainties, which necessitates robust strategies and techniques. With the increasing water depth, longer risers, and harsh pressure and temperature conditions; the risk of riser gas getting undetected get bigger. The lack of an integrated system to anticipate the controlling parameters at the choke below the BOP constrains the tackling operations and exacerbate the side effects of oil and gas well blowouts. This leads to an urgent need for an extensive study to address the riser gas unloading (RGU) events.
This study encompasses the development of a robust model that can characterize the effect of different parameters such as temperature, mud types, back pressure, and solubility in RGU events. It also presents comparative results of oil-based and water-based mud systems, using a novel tool based on analytical and numerical models. The analytical model is constructed using combined gas law, heat transfer mechanism, and gas solubility and bubble point pressure concepts.
Results suggest that the oil-based mud (OBM) takes more time for gas unloading in comparison to the water-based mud. Also, a significant deviation was observed in unloading patterns while considering temperature effect. For the drilling fluid without temperature consideration, the gas unloading occur in a smaller span of time and at a higher depth. Overall, this paper will demonstrate the effect of different parameters affecting the gas unloading in the riser, and present a comparative study of different parameters using an analytical which can be used in the field to get an idea of gas prior to any response for abnormality.