Formation damage caused by simultaneous sulfur and asphaltene deposition

Although many oil reservoirs producing crude oils of different sulfur and asphaltene contents, deposition problems of sulfur and asphaltene components in porous media are investigated separately. The major objectives of this laboratory study are to investigate the simultaneous deposition of sulfur and asphaltene in porous media. To achieve these objectives, the influences of the following on the permeability damage of the reservoir rock were experimentally investigated: (1) crude-oil flow rate, (2) permeability of reservoir rock through which crude oil flows, and (3) concentrations of sulfur and asphaltene in the crude oil. A base run was conducted using the crude oil after removing sulfur and asphlatene. Ten dynamic flow experiments were carried out using different crude oils of different sulfur and asphaltene concentrations and under different flow rates. The crude oil was flooded through different rock permeabilities of 2.34, 6.23, 16.58, and 21.48 md and under different flow rates of 0.5, 1.0, 2.0, and 3.0 cc/min, respectively. No permeability reduction or pore plugging was measured for the base experiment. The results indicated that the increase of flow rate increases the formation damage because of simultaneous deposition of sulfur and asphaltene in the reservoir rock. Core samples of lower permeability showed more severe permeability damage than those of higher permeability for the same applied flow rate and the same sulfur and asphaltene content of the crude oil. Furthermore, the increase of asphaltene and/or sulfur content of the crude oil increases the rock damage. The attained results of this study highlighted the important role of formation damage of carbonate oil reservoirs containing oils with a considerable amount of sulfur and asphaltene. In addition, the study provides two empirical correlations capable of predicting the permeability damage rate as a function of flow rate or initial rock permeability. These correlations represent useful tools for semianalytical and simulation studies.