The idea of Bazhenov formation rocks wettability evolution held from hydrophilic mudstones to hydrophobic rocks. In addition, the conclusion of hydrophobicity was often based on solid organic matter in large quantities contained in Bazhenov formation rocks cannot be hydrophilic. Usual petrophysical studies in these rocks are concerned with great difficulties, so we have to find some innovative solutions. In this case, the five wells core material was tested on lyophilic properties by adsorption of water vapor. The results were very surprising: the entire section is either hydrophilic or neutral.
The problem of wettability determination is that the hydrophobization ratio is defined, in fact, as the difference amount of adsorbed water. Therefore, it can be assumed that a significant kerogen presence in the organic-matrix will produce stable values near zero of hydrophobic coefficient by adsorption method. In other words, the amount of water adsorbed on the extracted and not extracted surface will not differ radically, i.e. hydrophobic ratio will indicate surface hydrophilicity, while possible real hydrophobicity
To solve this problem the core material of two wells was complex investigated by nuclear magnetic resonance (NMR) with different fluid saturation: water and kerosene. The incremental spectra analyzed jointly to identify the preferential wettability by the spectrum shift to the short relaxation times. For easy comparison, the wettability coefficient based on the mean log times was designed to characterize the position of the spectra from each other. As a result, the distributions of wettability coefficient were obtained for two wells of the same deposit. One of it was corresponded to the adsorption method, the other - neutral or light-hydrophobic wetting throughout the section. In this case, an effect of organic matter influence is presented. Organic matter can be either solid or liquid. The amount of free organic material increases with the degree of organic matrix maturity that revealed in the different wells, even in a single field.
The estimation of kerogen content in mineral matrix of Bazhenov formation rocks was made by NMR and X-ray diffraction methods in comparison with results of geochemical technique. This model will clarify petrophysical data interpretation of NMR logging.References
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