Distribution Model of Fluid Components and Quantitative Calculation of Movable Oil in Inter-Salt Shale Using 2D NMR

Volatilization behavior of diesel oil-water-glass bead system exposed to freeze-thaw cycles

Volatilization plays an important role in the attenuation and redistribution of petroleum products in contaminated porous media. However, the volatilization behavior of petroleum products exposed to freeze-thaw cycles is not well understood. In this study, we investigated the volatilization behavior of diesel oil-water-glass bead systems under different freeze-thaw cycles. Low-field nuclear magnetic resonance (LF-NMR) was used to quantitatively and spatially monitor the mass loss of the diesel oil-water-glass bead system during volatilization. The mechanism of the influence of freeze-thaw cycles on volatilization in the diesel oil-water-glass bead system was analyzed. The results show that the freeze-thaw cycles have a significant effect on the volatilization rate of diesel oil and water. As the number of freeze-thaw cycles increases, the volatilization rate of diesel oil shows an overall downward trend while the volatilization rate of water shows an overall upward trend. The volatilization loss of the liquids (both diesel oil and water) is mainly due to the volatilization loss of water, indicating that water is more volatile than diesel oil in the diesel oil-water system. The spatial distribution of the diesel oil signal monitored by LF-NMR showed that diesel oil volatilizes mainly in the upper layer of the sample, associating with the preferential volatilization loss in the large pores. The lumped parameter λ related to the characteristic volatilization length LV was introduced to characterize the volatilization rate of diesel oil and water with the increase of volatilization time. For a diesel oil-water-glass bead system exposed to freeze-thaw cycles, the 1/ LV of diesel oil decreases exponentially and rapidly with increasing volatilization time, while the 1/ LV of water decreases almost linearly and slowly with increasing volatilization time. This different dependence of 1/ LV on volatilization time leads to the individual volatilization behavior of diesel oil and water.

Evaluating the Effect of New Gas Solubility and Bubble Point Pressure Models on PVT Parameters and Optimizing Injected Gas Rate in Gas-Lift Dual Gradient Drilling

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.