Features of the development of carbonate rocks with mixed wettability and determination of the initial oil saturation coefficient on the example of the Timan-Pechora province fields

UDK: 622.276.1/.4:552.54

Key words: wettability, carbonate rocks, core cleaning, oil saturation coefficient, saturation exponent

Authors: V.Ju. Terentyev(LUKOIL-Engineering LLC, RF, Moscow), I.P. Gurbatova (PermNIPIneft Branch of LUKOIL-Engineering LLC in Perm, RF, Perm), T.F. Dyakonova (Central Geophysical Expedition, RF, Moscow), M.S. Khokhlova (Gubkin Russian State University of Oil and Gas, RF, Moscow)

Understanding wettability formation plays an important role in optimizing oil recovery. Incorrect assumptions about the nature of the wettability of a formation can lead to irreversible complications in the design and inaccurate estimates of the initial geological reserves. If the reservoir is hydrophobic or intermediate wettability, but experiments using cleaning cores with a hydrophilic wettability, the displacement parameters in water flooding may be overstated. The coefficients of the displacement can also be specified properly if the core has a fractional or mixed wettability. Using a standard sample preparation for petrophysical studies of carbonate rocks with altered wettability leads to an overestimation of the quantities of oil saturation on log data and, consequently, to errors in the calculation of geological and recoverable reserves of oil and ineffective choice of development options. Possible causes of the contradictions are not adequate type of wettability preparation of samples for research, the use of samples is not natural, and wettability alteration, use as saturating and displacing agents of their models, instead of natural fluids particular deposits, as well as use of small samples of standard size, which simplifies the structure of carbonate rock pore space. The results of our core research using new laboratory techniques, while that of standard size samples, virtually remove contradictions in the values of oil saturation from the core and log data. Wettability type must be determined before the petrophysical studies and experiments to conduct themselves on the samples with the natural or restored-state wettability. According to the standard procedure can be carried out petrophysical study, if it is known beforehand that the reservoir hydrophilic, or to determine the parameters on which the wettability effects do not have a significant impact, for example, the coefficients of porosity and absolute gas permeability.
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