High Residual Oil Saturation Research Articles

Differences in Behavior of Fresh and Aged East Texas Woodbine Cores

Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 86–91. Abstract Laboratory experiments have shown profound differences in the behavior of so-called "fresh cores" from the East Texas field and of the same cores after extraction with organic solvents. The residual oil saturation remaining after waterflooding fresh cores was appreciably lower than the corresponding saturations after flooding extracted cores. This behavior was also reflected in the water-oil relative permeability-saturation relations, which were more favorable for high oil recovery from the fresh cores. These differences were evident not only in the amount of residual oil left after water flooding, but also in the saturation water remaining in the core after displacement by oil. Residual water saturation after displacement of water by oil was higher in the fresh cores than in the extracted cores. Capillary pressure-saturation relations were also different for the fresh and extracted cores. Imbibition experiments indicated that both fresh and extracted East Texas cores imbibed water spontaneously, but the rate of imbibition of water was higher for samples after extraction than it was for fresh core material. Introduction Several years ago a series of waterflooding tests was made in the laboratory on a number of Woodbine core samples from the East Texas field. These samples had been stored in containers open to the air and were extracted with organic solvents before they were subjected to the laboratory tests. After water flooding, the residual saturation of kerosene, which was the oil used in the tests, was found to average about 30 per cent. This saturation was higher than expected. In investigating the circumstances which might have been responsible for such a high residual oil saturation, attention was given to possible changes in wetting properties of the rock brought about by the procedure employed in extracting the cores. Preliminary results indicated that the explanation for the high residual oil saturation lay in the wetting behavior of the cores, though what effect extraction had on this behavior was not clear. In consequence, the work described in this report was undertaken in an attempt to investigate the mechanism responsible, and to ascertain the actual residual oil saturation to be expected in the reservoir after water flooding. It was soon found that there were profound differences in the behavior of so-called "fresh cores" from the East Texas field and of the same cores after extraction with organic solvents. These differences were evident not only in the amount of residual oil left after water flooding, but also in the saturation of water remaining in the core after displacement by oil.