Experimental and analytical studies of hydrocarbon yields under dry-, steam-, and steam with propane-distillation



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Texas A&M University


Recent experimental and simulation studies -conducted at the Department of Petroleum Engineering at Texas A&M University - confirm oil production is accelerated when propane is used as an additive during steam injection. To better understand this phenomenon, distillation experiments were performed using seven-component synthetic oil consisting of equal weights of the following alkanes: n-C5, n-C6, n-C7, n-C8, n-C9, nC10, and n-C15. For comparison purposes, three distillation processes were investigated: dry-, steam-, and steam-propane-distillation, the latter at a propane:steam mass ratio of 0.05. The injection rate of nitrogen during dry-and steam-distillation was the same as that of propane during steam-propane distillation, 0.025 g/min, with steam injection rate kept at 0.5 g/min. The distillation temperatures ranged from 115?C to 300?C and were increased in steps of 10?C. The cell was kept at each temperature plateau (cut) for 30 minutes. Distillation pressures ranged from 0 psig for dry distillation to 998 psig for steam-and steam-propane distillation. The temperature-pressure combination used represented 15?C superheated steam conditions. Distillate samples were collected at each cut, and the volume and weight of water and hydrocarbon measured. In addition, the composition of the hydrocarbon distillate was measured using a gas chromatograph. Main results of the study may be summarized as follows. First, the hydrocarbon yield at 125?C is highest with steam-propane distillation (74 wt%) compared to steam distillation (58 wt%), and lowest with dry distillation (36 wt%). This explains in part the oil production acceleration observed in steam-propane displacement experiments. Second, the final hydrocarbon yield at 300?C however is the same for the three distillation processes. This observation is in line with the fact that oil recoveries were very similar in steam- and steam-propane displacement experiments. Third, based on the yields of individual hydrocarbon components, steam-propane distillation lowers the apparent boiling points of the hydrocarbons significantly. This phenomenon may be the most fundamental effect of propane on hydrocarbon distillation, which results in a higher yield during steam-propane distillation and oil production acceleration during steam-propane displacement. Fourth, experimental K-values are higher in distillations with steam-propane for the components n-hexane, n-heptane, n-octane, and n-nonane. Fifth, vapor fugacity coefficients for each component are higher in distillations with steam-propane than with steam. Finally, Gibbs excess energy is overall lower in distillations with steam-propane than with steam. The experimental results clearly indicate the importance of distillation on oil recovery during steam-or steam-propane injection. The experimental procedure and method of analysis developed in this study (for synthetic oil) will be beneficial to future researchers in understanding the effect of propane as steam additive on actual crude oils.