Flow behavior of N2 huff and puff process for enhanced oil recovery in tight oil reservoirs
In the present work, the potential of N2 huff and puff process to enhance the recovery of tight oil reservoir was evaluated. N2 huff and puff experiments were performed in micromodels and cores to investigate the flow behaviors of different cycles. The results showed that, in the first cycle, N2 was dispersed in the oil, forming the foamy oil flow. In the second cycle, the dispersed gas bubbles gradually coalesced into the continuous gas phase. In the third cycle, N2 was produced in the form of continuous gas phase. The results from the coreflood tests showed that, the primary recovery was only 5.32%, while the recoveries for the three N2 huff and puff cycles were 15.1%, 8.53% and 3.22%, respectively.The recovery and the pressure gradient in the first cycle were high. With the increase of huff and puff cycles, and the oil recovery and the pressure gradient rapidly decreased. The oil recovery of N2 huff and puff has been found to increase as the N2 injection pressure and the soaking time increased. These results showed that, the properly designed and controlled N2 huff and puff process can lead to enhanced recovery of tight oil reservoirs.
Experimental analysis on reservoir blockage mechanism for CO2 flooding
Abstract The slim-tube experiment, component analysis experiment and microscopic simulation experiment are used to analyze the phenomena of reservoir blockage and drop of oil production rate, and to find out the reservoir blockage mechanisms in the process of carbon dioxide flooding. The slim-tube experiment shows that the effect of carbon dioxide flooding was poor under low displacement pressure, and the higher the displacement pressure, the better the effect of flooding. When the displacement pressure exceeded the minimum miscibility pressure, reservoir blockage could occur, affecting the reservoir productivity significantly. Component analysis and microscopic modeling experiments show that oil component differentiation could occur after oil contacted with carbon dioxide. Under low displacement pressure, component differentiation was not significant, so reservoir blockage did not occur; but when the displacement pressure was higher, aromatics in oil were extracted rapidly by carbon dioxide, resulting in quick deposition of non-hydrocarbons and asphalt and the blockage of pore-throats in reservoirs. Therefore, controlling the displacement pressure is the main measure to prevent reservoir blockage. The best pressure of carbon dioxide flooding should be near the minimum miscible pressure, pressure, too high or too low, is not good for carbon dioxide flooding.
Effect of Aeration and Agitation Regimes on Lipase Production by Newly Isolated Rhodotorula mucilaginosa–MTCC 8737 in Stirred Tank Reactor Using Molasses as Sole Production Medium
The influence of media and process parameters (aeration and agitation) on fermentation broth rheology and biomass formation has been studied in 1.5-l stirred tank reactor for lipase production using Rhodotorula mucilaginosa MTCC 8737. Molasses, as sole production medium, is used for lipase production by varying aeration (1, 2, and 3 vvm) and agitation speeds (100, 200, and 300 rpm). Maximum lipase activity of 72 U/ml was obtained during 96 h of fermentation at 2 vvm, 200 rpm, pH 7, and 25 ± 2°C temperature. Lipase production kinetics with respect to dry cell weight of biomass showed YP/S of 25.71 U/mg, specific product formation of 10.9 U/mg DC, and YX/S 2.35 mg/mg. Maximum lipase activity (MC 2) of 56 U/ml was observed at 1% molasses, and a further increase in the molasses concentration of (%) 1.5 and 2 inhibited the product formation of lipase with 15 and 8.5 U/ml, respectively. The production kinetics of molasses media showed YP/X was 14 U/mg DC, YP/S 16 U/mg, and YX/S 1.14 mg/mg during 96 h of bioreactor operation. The kLa values for all batches (MC 1–MC 4) at 96 h of fermentation were 32, 28, 21, and 19/h, and the |oxygen transfer rate were 54.4, 56, 35.7, and 17.29 mg/l h, respectively. Increase in molasses concentration resulted in decreased lipase activity by increase in viscosity of the fermentation broth.