Certain additives used in drilling and completion fluids may alter the wettability of core. For example, the surfactants in invert-oil-emulsion drilling muds are known to al,ter the wettability of core. Because routine cleaning methods do not remove these surfactants, core that is to be used for special laboratory analyses, such as relative permeability, capillary pressure, and saturation exponent, is left with an altered wettability. Experiments with such core will obviously produce erroneous data. To obtain reliable results, cleaning methods must be developed to remove these surfactants, allowing restoration of plugs to their natural wettability. Once the core is cleaned, the wettability of the cleaned core can be restored by saturating with synthetic formation brine and uncontaminated reservoir crude, then aging at the reservoir temperature.This report ranks the efficiency of solvents in removing surfactants from plugs contaminated with invert-oil-emulsion drillingmud filtrate. Eight solvents for Berea sandstone and seven solvents for Guelph dolomite have been ranked after Dean-Stark extraction of mud surfactants using the U.S. Bureau of Mines (USBM) wettability index. The best solvent for both rock types was a 50/50 mixture of toluene/methanol, or the equivalent, containing 1 % ammonium hydroxide. Toluene, the most commonly used solvent for core cleaning, was one of the poorest solvents tested. The solvents that are effective in removing surfactants can be used to clean contaminated core.
The β decay of tritium in the gaseous tritium-cyclopropane system initiates reactions forming various tritiated compounds. Identified products are cyclopropane, propane, propylene, isobutane, ethane, ethylene, and acetylene. Dependence of the labeling yields on T2 concentration clearly showed that energetic electrons as well as the decay species (He3T)+ initiated the labeling processes. Ionic and/or hot-atom reactions are assumed to occur to explain the effects of nitric oxide and temperature on the labeling yields.
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