Abstract
Gas-lift dual gradient drilling (DGD) is a solution for the complex problems caused by narrow drilling windows in deepwater drilling. Investigations are lacking on using oil-based drilling fluid in DGD, which is the principal novel idea of the present study. This research compares the results obtained from two new models with those of Standing’s correlations for solubility and bubble point pressure. Nitrogen was selected as the injection gas, then the PVT behavior of drilling fluid (oil/water/Nitrogen) in gas-lift DGD was evaluated and compared by coding in MATLAB. Then, these results were used to calculate the bottom hole pressure and finally investigate the optimization of injected gas flow rate. According to the achieved results, the Standing model has some errors in evaluating the PVT behavior of “Nitrogen and oil-based drilling fluids” and is not recommended for the mixtures in the gas-lift DGD. Regarding optimizing gas flow rate, a discrepancy was observed between pressure values obtained from the new models and the Standing model for the case of high liquid flow rates at low gas flow rates because of the difference in PVT parameters. The developed codes are deposited on an online data repository for future users. This study lays the foundation for better planning of drilling in deepwater drilling projects.
Highlights
As the demand for oil and gas continues to rise, exploration and drilling operations in deep water are being developed by many companies
It is worth noting that this study focused on the feasibility of implementing oil-based drilling fluid in the gas-lift dual gradient drilling (DGD) in the South China Sea
Tion and the bubble point equation, on PVT parameters was compared with the case of using Standing correlations for solubility and bubble pressure
Summary
As the demand for oil and gas continues to rise, exploration and drilling operations in deep water are being developed by many companies. In the development of these areas, the depleted reservoirs have led the drilling industry to encounter new technical challenges due to the harsh conditions at great depths. On the other hand, increasing the casing number has improper impacts on logging, cementing, and perforation operations, and above all, it could reduce the production rate. The gas lift dual gradient drilling, as a part of managed pressure drilling (MPD) technology, is one method to overcome the problems met in deep water and in the reservoirs with narrow drilling windows, where the pore pressure and fracture pressure [1,2] are close.
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