Abstract
American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
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Abstract
This work was principally concerned with an experimental study of oil recovery from a porous medium by the injection of a light hydrocarbon slug, followed by a steam slug, which is in turn driven by a conventional waterflood. An attempt was made to simulate the experiments by use of a cell model. The experiments involved fluid displacements in two glass bead packs having a rectangular internal cross-section of 1.75 × 3.75 in and 48 in length, overlain and underlain by 1.5 ft thick sand packs to simulate the adjacent formations.
The core initially contained a residual oil saturation or a high initial oil saturation, corresponding to the irreducible water saturation. Drakeol 33 and Drakeol 35 (viscosities of 152 and 209 cp, respectively) were employed as the inplace oils, while isooctane, Soltrol C, Kendex 0837, Drakeol 9, Drakeol 15, and three mixtures of Soltrol C and Drakeol 33, Kendex 0837 and Drakeol 9, and Drakeol 9 and Drakeol 35 (viscosities of 0.5, 1.3, 11.3, 23.4, 49.4, 6.4, 17.4, 73.3 cp, respectively) were used as the light hydrocarbon slug materials. Light hydrocarbon slug sizes of 5, 10, and 25% PV were employed, while the steam slug size ranged from 19 to 66% PV, with an average of 35.7% PV. The steam injection rate ranged from 11 to 150 ft/day.
It was found that the light hydrocarbon slug injected prior to the steam slug in a core initially containing a residual oil saturation improved the oil recovery as compared to a straight steam slug run. The light hydrocarbon, in view of the prevailing adverse mobility ratio, mixes with the original inplace oil, and helps to lower its viscosity. This viscosity is further reduced by the heat from the injected steam slug, leading to an improvement in the mobility ratio, and hence an improvement in the displacement efficiency. A large proportion of the light hydrocarbon slug is recovered by the steam distillation effects. It is concluded that from the recovery ratio (volume of oil recovered divided by hydrocarbon slug volume) point of view, it is advantageous to use a low viscosity light hydrocarbon slug, and a small slug size. The optimum slug size depends on the in-place oil, as well as the steam slug size, for a given steam temperature.
The temperature profiles and the heat loss rate measurement indicated that the combination, light hydrocarbon slug-steam slug, process utilizes the maximum amount of heat injected, hence increasing the thermal efficiency of the process. process.