Adsorption of Asphaltenes and Water on Reservoir Rock Minerals

Abstract

Abstract New data relating to the adsorption of asphaltenes on reservoir rock minerals are reported. The data were obtained by contacting samples of several different clay mineral types, as well as of Berea sandstone, with toluene solutions of a petroleum asphaltene fraction. This material was petroleum asphaltene fraction. This material was recovered from a deposit on the tubing string of a producing well. It was characterized with respect producing well. It was characterized with respect to molecular weight and elemental composition. Adsorption isotherms were determined and found to be of the Langmuir type, indicating monolayer adsorption. For each of the samples an independent surface area measurement was made. This permitted the probable size of the adsorbed asphaltene particles to be estimated. The effect of water on particles to be estimated. The effect of water on the adsorption of asphaltenes on kaolinite was also determined. It was found that adsorption was reduced but not eliminated by the presence of water. In these experiments the water was either pre-adsorbed on the clay or simply dissolved in the pre-adsorbed on the clay or simply dissolved in the solvent. The amount of co-adsorbed water corresponded to 30-50 monolayers, indicating the probable formation of liquid bridges of water probable formation of liquid bridges of water between clay particles. estimates were obtained for the magnitude of the microscopic toluene/water contact angles which characterize these liquid bridges. Introduction Various problems arising in petroleum reservoir exploitation involve the interaction of pore-filling fluids with the minerals which are exposed at the pore surfaces in reservoir rock. For example, the pore surfaces in reservoir rock. For example, the wettability of a reservoir is believe, to be strongly dependent on the extent of heavy ends adsorption. Although the nature of this dependence has yet to be expressed in quantitative terms, it appears that heavy ends adsorption will affect, in the first place, the relative proportions of the total pore surface area which are in contact with each of the two fluid phases, oil and brine. If the fluid in question is the oil phase, the fractional surface area for this fluid may be termed the surface oil saturation. Thus, a general objective of much research on wettability has been to develop a method for measuring the surface oil saturation of reservoir rock samples. Another phase of wettability research has been directly focused on the process of heavy ends adsorption. This has involved the quantitative determination of the extent and nature of the adsorption of a well-characterized asphaltene fraction on various rock and mineral surfaces. The present paper reports the results of further work of this kind. A specific objective was to determine whether thin films of water on the surface of a mineral would prevent or modify the subsequent adsorption of asphaltenes. The fact that adsorbed water affects the adsorption of petroleum heavy ends has been alluded to in the literature. However, it is believed that the present study is the first to attempt to quantify the effect by means of adsorption measurements on clay mineral surfaces. The manner in which heavy ends adsorption determines the magnitude of the surface oil saturation of reservoir rocks is not known at present. It has been proposed that a complex present. It has been proposed that a complex interplay of capillary forces thin film forces and adsorption forces is involved. Other studies on wettability suggest that in many instances this type of interplay gives rise to a state of mixed wettability. In the present pacer, attention is restricted to the present pacer, attention is restricted to the question of how asphaltene adsorption is affected by the presence of adsorbed water. Isotherms are reported for various amounts of pre-adsorber water on a kaolinite surface. Also, oil/water contact angle data are reported for several surfaces which had been prepared by compacting a sample of asphaltene-covered clay. The principal constituents of petroleum which absorb on clay minerals have been identified in previous work as asphaltenes and resins. previous work as asphaltenes and resins. P. 249