Suppression of Asphaltene Adsorption in Porous Media

Thesis (Master's)--University of Washington, 2017-06This work seeks to investigate the adsorption/deposition of asphaltene clusters and nanoaggregates in a porous medium, under flow conditions and at high pressures. It also explores the strategies to reduce or prevent the adsorption/deposition. Asphaltenes are highly aromatic and heavy fractions present in crude oil. Their adsorption or deposition causes problems during production due to clogging of the pore structure of the rock as well as subsequently fouling downstream piping and fittings. The porous medium used in this study is 140 mesh silica (100 micron) packed into an HPLC (high performance liquid chromatograph) column through which dilute solutions of asphaltenes in a weak solvent (toluene and tetradecane 50 % by wt.) are pumped. Langmuir isotherms fit well to the adsorption results. Saturation asphaltene adsorption (Γmax) of about 1250 mg/m2 is obtained for silica particles. To reduce or prevent such deposition, silica surface is modified using HTAB (hexadecyl trimethylammonium bromide), HMDS (Hexamethyldisiloxane) and OTS (Octadecyltrichlorosilane) to form a protective layer. Subsequent HPLC studies indicate that the saturation asphaltene adsorption on the treated silica has been reduced to 909.10 mg/m2, 833.33 mg/m2 and 588.23 mg/m2 respectively. To investigate the effects of adsorption/deposition on the porosity of the silica column, dilute solution of a high molecular weight asphaltene mimic, SEPTON 4099, in a similar solvent is pumped through the column under high pressure. Adsorption/deposition is monitored by changes in the pressure required to sustain a given flow rate, which is analyzed to give the resulting change in bed porosity, as deduced using Ergun analysis. Adlayer of thickness up to 3.6 μm is found to develop over a period of 60 hours. To reduce or prevent such deposition, the silica is pre-treated with HTAB to form a protective layer. Subsequent HPLC studies indicate that the polymer adsorption on the treated silica has been reduced to less than 50%