It is increasingly thought that knowing a reservoir's wettability is,essential for establishing the Special Core Analysis procedures in order to estimate Swi and So,However,the conditions(T,P,kind of oil)under which this parameter is evaluated can have an important influence on the measurement result,and contradictory results on this subject are found in the literature.This affects the viability of the extrapolation to reservoir conditions hm results obtained in the laboratory under different conditions.The most reliable way to evaluate the wettability of reservoir rock is to reproduce reservoir conditions;however,no description of satisfactory apparatus for making this kind of measurement can be found in the literature.This paper describes the first apparatus which can carry out the Amott-Harvey test under reservoir conditions.The influence of the conditions selected for the wettability measurements(T,P,kind of oil)on the wettability index obtained is studied for four reservoirs(three sandstone and one carbonate).For sandstone,it is demonstrated that an increase in temperature often(but not always)increases the rock's affinity for water,but this increase strongly depends on the reservoir rock considered.For the carbonate,no influence of thermodynamic conditions has been observed.Finally,it is shown that,currently,it is impossible to predict the change in wettability that occurs when the previously considered conditions vary.Each reservoir is unique,and assessing wettability under reservoir conditions remains the most reliable and strongly recommended option.
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