Formation Damage Due To Simultaneous Sulfur and Asphaltene Deposition

Abstract

Abstract Although many oil reservoirs are producing crude oils of different sulfur and asphaltene contents, deposition problems of sulfur and asphaltene components in porous media were 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 (1) crude oil flow rate, (2) reservoir rock permeability through which crude oil flows and (3) concentrations of sulfur and asphaltene in the crude oil, on permeability damage of the reservoir rock were experimentally investigated. 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 permeability 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. The results indicated that the increase of flow rate increases the formation damage due to simultaneous deposition of sulfur and asphaltene in the reservoir rock. Core samples of lower permeability showed more severe permeability damage than that ones 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 enlightened the important role of formation damage of carbonate oil reservoirs containing oils of considerable amount of sulfur and asphaltene. In addition, the study provides two empirical correlations capable to predict the permeability damage rate as a function of flow rate, or initial rock permeability. These correlations represent useful tools for semi-analytical and simulation studies. Introduction and Review Almost all deep sour gas reservoirs and many oil reservoirs contain elemental sulfur as a dissolved species in virtually. Reduction in pressure and temperature induced sulfur precipitation by a reduction in the solubility of the sulfur in the gas and/or oil phase beyond its thermodynamic saturation point. These changes occur during production operations and can result in sulfur deposition in the reservoir, wellbore and surface facilities. Deposition of elemental sulfur in the near well bore area may significantly reduce the inflow performance of sour-gas wells. In addition, oil reservoirs all over the world suffer of simultaneous sulfur and asphaltene deposition problems in porous media and cause problems in production facilities. Investigation of sulfur deposition in porous media has little attention while asphaltene nature and deposition in porous media has been covered extensively. Furthermore, the investigation of simultaneous sulfur and asphaltene deposition has not been studied in spite of the expected problems of formation damage and facility corrosion.