Global retention model

Simultaneous interpretive methods (table 5.7d) provide a way to locate the global optimum from a relatively low number of experiments. The price that should be paid for this very important advantage of these methods is an increased effort from the chromatographer to provide knowledge (to model the retention surfaces), increased computational requirements and the necessity to recognize all the individual solutes in each chromatogram. The reliability of the final result will depend on the accuracy of the model. 

The thermo-hydrological calculations have indicated that it is possible to choose appropriate hydrological parameters in order to obtain a distribution of saturation similar to the one prevailing in the in situ test. Intrinsic permeability was taken from the fractures and retention curve was taken from the matrix. Relative permeability for gas and for liquid had to be modified. None of the functions valid for the matrix or the fracture were appropriate. The problem in fact, is that relative permeabilities are controlled by degree of saturation in the fracture and this model used a global degree of saturation. Therefore, relative permeability functions should undergo variations near full saturation because the fractures desaturate for low capillary pressures compared to the matrix. 

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