Steam Distillation of Crude Oils

Abstract

Abstract The objectives of this investigation were to generate crude oil steam distillation data for the prediction of phase behavior in steamflood simulation and to correlate the steam distillation yields for a variety of crude oils. Thirteen steam distillation tests were run on 10 crude oils ranging in gravity from 9.4 to 37 deg. API (1.004 to 0.840 g/cm3). In each test the crude was steam distilled sequentially at about 220, 300, 400, and 500 deg. F (104, 149, 204, and 260 deg. C). The cumulative steam distillation yields at 400 deg. F (204 deg. C) ranged from about 20 to 55 vol%. Experimental results showed that crude oil steam distillation yields at steamflood conditions are significant, even for heavy oils. The effects of differences in steam volume throughput and steam temperature were taken into account when comparing yields for different crudes or repeat runs on the same crude. Steam distillation yields show a high correlation with crude oil API gravity and wax content. Introduction Steam distillation is an important steamflood oil recovery mechanism, especially in reservoirs containing light oils. Injected steam heats the formation and eventually forms a steam zone, which grows with continued steam injection. A fraction of the crude oil in the steam zone vaporizes into the steam phase according to the vapor pressures of the hydrocarbon constituents contained in the crude oil. The hydrocarbon vapor is transported through the steam zone by the flowing steam. Both the steam and hydrocarbon vapor condense at the steam front to form a hot-water zone and a hydrocarbon distillate bank. The vaporization, transport, and condensation of the hydrocarbon fractions is a dynamic process that displaces the lighter hydrocarbon fractions and generates a distillate bank that miscibly drives reservoir oil to producing wells. The effect of steam distillation on oil recovery has been investigated in several laboratory studies, steamf lood field tests, and in simulation studies. In a critical review of steam flood mechanisms, Wu discussed the steam distillation mechanism in detail. Wu and Brown reported steam distillation yields for six crude oils ranging from 9 to 36 deg. API (1.007 to 0.845 g/cm3). When plotted against their steam distillation correlation parameter, Vw/Voi (the ratio of collected steam condensate, Vw, and initial oil volume, Voi), the yields were independent of the porous medium used, steam-injection rate, and initial oil volume. For the crude oils tested, they concluded that changing the saturated steam pressure and temperature had an insignificant effect on yield, but superheating the steam from 471 to 600 deg. F (244 to 316 deg. C) significantly increased the yield. Wu and Elder reported steam distillation yields for 16 crude oils ranging from 12 to 40 deg. API (0.986 to 0.825 g/cm3). Yields ranged from 12 to 56% of initial oil volume at a distillation temperature and pressure of 380 deg. F and 200 psig (193 deg. C and 1.379 MPa). Yields at Vw/Voi = 15 were correlated with three parameters:simulated distillation temperature of the oil at 20% yield,oil viscosity, andoil API gravity. The simulated distillation obtained by gas chromatography closely approximates the true boiling-point distillation as determined by ASTM distillation. The simulated distillation temperature at 20% yield gave the closest correlation with steam distillation yield. SPEJ P. 265^