Evaluation of experimental methods to determine wettability
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Two methods to evaluate the wettability of carbonates have been investigated: Aqueous cationic surfactant solutions contact angles on oil-wet calcite crystals, and imbibition time of surfactant drops into oil-wet outcrop chalk slices, both immersed in n-decane during measurements. The procedure to measure contact angles offered good repeatability, and the results were according to theory. However, the effectiveness of the surfactants was ordered differently depending on which pure carboxylic acid was used to create oil-wet crystals, and it would perhaps be desirable to use crude oil instead. The repeatability in the imbibition experiments was poor, and water and/ or brine often imbibed faster than surfactants, this was attributed to weakly oil-wet chalk slices. Ignoring water and brine, the effectiveness of the surfactants were ordered like in Amott-tests reported by Standnes and Austad (2000). Overall in both experiments, C12TAB and C14TAB were the most effective wettability modifiers. In the imbibition experiments, oil expulsion from the chalk slices was also observed.
Master's thesis in Petroleum engineering