Untersuchungen zur Benetzbarkeit von Erdölreservoir- und Muttergesteinen durch Kontaktwinkelmessungen an Mineralien und Gesteinen

Oil reservoir wettability, in conjunction with a number of other factors, determines the oil recovery rate. The aim of this investigation was to correlate oil reservoir wettability with mineral or oilwater composition and temperature. Parameters which decrease water-wettability were of special interest. Wettability was determined by measuring contact angles of idealized oil/water systems against polished reservoir related minerals and reservoir rocks. The "Dynamic Wilhelmy Method" was used. Also, contact angles at polished source rock plates were conducted. Quartz, calcite, limestone, dolomite, albeit, kaolinite, muscovite and toluene-extracted source rockplates are water wet with advancing contact angles < 36° against water/hexadecane or water/toluene when the plates were not precontacted in either of the organic phase. The receding angle is 0°. The unextracted source rock is hybrid wettable. A substitution of water by a 0.1 M MgSO$_{4}$ solution increases the contact angles at all materials. Other electrolytes which contain multivalent cations increase the contact angle at quartz. In contrast to the receding angle, the advancing angle is strongly material dependent when the slices are soaked (72h at 20$^\circ$C) in either of the organic phases, prior to contact angle measurement.Limestone, dolomite, albeit and the unextracted source rock become hybrid wettable against water/toluene. Against water/hexadecane only albeit is hybrid wettable. The hydrophobicity against hexadecane or toluene and water, 0.1 M NaCl or CaCl$_{2}$ solutions increases in the order: quartz < carbonates < source rocks. The differences are smaller when the electrolyte is MgSO$_{4}$ or when the soaked plates are briefly precontacted with water prior to contact angle measurement. The latter phenomena is explained by the displacement of hexadecane and toluene from the surface by water. Pre-soaking the slices 72h in hexadecane or toluene at 80 $^\circ$C hydrophobizes the slices more than presoaking at 20°C. An almost uniform receding angle of 50$^\circ$ is observed. The advancing angle at quartz is again lower than that at the carbonates, albeit, muscovite and kaolinite. The advancing angle at quartz against water/n-alkane is proportional to the chain length of the n-alkane. Quartz gets hydrophobic against water/hexadecane after soaking for 72h at 110$^\circ$C in hexadecane. Wettability is also dependent an slice composition when the solids are soaked in anionic or cationic surfactant solutions prior to contact angle measurement against the surfactant solution and hexadecane or toluene. Quartz gets hydrophobic when soaked in the cationic surfactant solution, while limestone and albeit get hydrophobic when soaked in an anionic surfactant solution. The results are explainable through electrostatical arguments. Soaking quartz in a 0.1 M mixed surfactant solution (which contains both an anionic and a cationic surfactants) hydrophobizes the quartz against hexadecane and the mixed surfactant solution to a greater extent than when only one of the ionic surfactants are employed. Quartz and albeit are more hydrophobic against a 1mM solution of stearic acid in hexadecane and a 1mM DTAB- or SDS-solution than against a 1mM solution of stearic acid in hexadecane/water or hexadecane/ImM DTAB- or SDS-solution. The wettability against toluene solutions of oil fractions (deasphalted oil, resins, asphaltenes) and water depends on the mineral. It appears that wettability is more influenced by the type of mineral than by the oil composition. Quartz is independent of the oil fraction hybrid wettable, while albeit and muscovite are oil wettable. The advancing angle increase in the order: quartz < calcite < muscovite < albeit. The Colloids do not particularly hydrophobize the minerals. Coating experiments applying the Langmuir-Blodgett technique show that wettability shifts inducedby coating a mineral slice with a monornolecular layer of a surfactant are dependent on the outmost part of the molecule which is adjacent to the fluid. The structure of the hydrophilic portion of the monolayer and substrat determines the strength of the sorptive bonding. Monolayers of stearic acid and 5$\beta$-cholanic acid induce a hybrid wettability limestone and albeit against hexadecane water. The transformation of these results to natural systems is questionable since the wettability of thesystem reservoir rock-oil/brine depends on the composition of all three phases. Yet the composition is unique to each reservoir. However, the results do strongly suggest that the mineral reservoir type determines wettability to a larger extent than crude oil composition. Reservoir rocks composed of quartz would be more hydrophilic than rocks made out of calcite. The wettability of calcite and dolomite rocks would be approximately equal. Muscovite and albeit would hyrophobize carbonate reservoirs moderately and quartz reservoirs strongly. Multivalent electolytes (except MgSO$_{4}$) would hydrophobize quartz reservoirs but not carbonate reservoirs. However, MgSO$_{4}$ in a brine would hydrophobize both carbonate and quartz reservoirs. An increase in the temperature of a reservoirwould hydrophobize all minerals