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.
References
1. Mikhaylov N.N., Semenova N.A., Sechina L.S., The influence of microstructure
wetting on the petrophysical characteristics of the reservoir rocks
(In Russ.), Karotazhnik, 2011, no. 7, pp. 163–172.
2. Kuz'min V.A., Mikhaylov N.N., Skibitskaya N.A. et al., Results of the electronmicroscopic
research on the impact of microstructural factors of reservoir
space on the oil saturation pattern (In Russ.), Geologiya nefti i gaza = The journal
Oil and Gas Geology, 2015, no. 3, pp. 34–44.
3. Edmonton W.A., Fundamentals of wettability (In Russ.), Neftegazovoe
obozrenie, 2007, V. 19, no. 2(Summer), pp. 57–75.
4. Gurbatova I.P., Kuz'min V.A., Mikhaylov N.N., Influence of pore space structure
on the scale effect in studying permeability storage capacity of complicatedly
built carbonate reservoirs (In Russ.), Geologiya nefti i gaza = The journal
Oil and Gas Geology, 2011, no. 2, pp. 74–82.
5. Gudok N.S., Bogdanovich N.N., Martynov V.G., Opredelenie fizicheskikh
svoystv neftevodosoderzhashchikh porod (Determination of physical properties
of oil-and- water containing rocks), Moscow: Nedra Publ., 2007, 592 p.
6. Tiab D., Donaldson E C., Petrophysics: theory and practice of measuring
reservoir rock and fluid transport, Elsevier Inc., 2004, 926 p.
7. Longeron D.G., Argaud M.J., Bouvier L., Resistivity index and capillary pressure
mesurements under reservoir conditions using crude oil, SPE 19589, 1989.
8. Cuiec l., Longeron D., Pacsirszky J., On the necessity of respecting reservoir
conditions in laboratory displacement studies, SPE 7785, 1979.
9. Pairoys F., Al-Zoukani, Nicot B. et al., Multi-physics approach for aging assessment
of carbonate rocks, SPE 149080, 2011.
10. Cuiec L., Rock/crude-oil interactions and wettability: an attempt to understand
their interrelation, SPE 13211, 1984.
11. Metodicheskie rekomendatsii po podschetu zapasov nefti i gaza ob’emnym
metodom. Otsenka kharaktera nasyshchennosti po dannym GIS
(Guidelines for the calculation of reserves of oil and gas by volumetric
method. Assessment of the nature of saturation according to well logging):
edited by Petersil’e V.I., Poroskun V.I., Yatsenko G.G., Moscow –Tver: Publ. of
VNIGNI, 2003, 260 р.
12. Vendel’shteyn B.Yu., Rezvanov R.A., Geofizicheskie metody opredeleniya
parametrov neftegazovykh kollektorov (pri podschete zapasov i proektirovanii
razrabotki mestorozhdeniy) (Geophysical methods of determining
the parameters of oil and gas reservoirs (for calculation of reserves and reservoir
engineering))., Moscow: Nedra Publ., 1978, 318 p.
13. Cuiec L.E., Restoration of the natural state of core samples, SPE 5634, 1975.
14. Gant P.L., Anderson W.G., Core cleaning for restoration of native wettability,
SPE 14875, 1988.
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.
References
1. Mikhaylov N.N., Semenova N.A., Sechina L.S., The influence of microstructure
wetting on the petrophysical characteristics of the reservoir rocks
(In Russ.), Karotazhnik, 2011, no. 7, pp. 163–172.
2. Kuz'min V.A., Mikhaylov N.N., Skibitskaya N.A. et al., Results of the electronmicroscopic
research on the impact of microstructural factors of reservoir
space on the oil saturation pattern (In Russ.), Geologiya nefti i gaza = The journal
Oil and Gas Geology, 2015, no. 3, pp. 34–44.
3. Edmonton W.A., Fundamentals of wettability (In Russ.), Neftegazovoe
obozrenie, 2007, V. 19, no. 2(Summer), pp. 57–75.
4. Gurbatova I.P., Kuz'min V.A., Mikhaylov N.N., Influence of pore space structure
on the scale effect in studying permeability storage capacity of complicatedly
built carbonate reservoirs (In Russ.), Geologiya nefti i gaza = The journal
Oil and Gas Geology, 2011, no. 2, pp. 74–82.
5. Gudok N.S., Bogdanovich N.N., Martynov V.G., Opredelenie fizicheskikh
svoystv neftevodosoderzhashchikh porod (Determination of physical properties
of oil-and- water containing rocks), Moscow: Nedra Publ., 2007, 592 p.
6. Tiab D., Donaldson E C., Petrophysics: theory and practice of measuring
reservoir rock and fluid transport, Elsevier Inc., 2004, 926 p.
7. Longeron D.G., Argaud M.J., Bouvier L., Resistivity index and capillary pressure
mesurements under reservoir conditions using crude oil, SPE 19589, 1989.
8. Cuiec l., Longeron D., Pacsirszky J., On the necessity of respecting reservoir
conditions in laboratory displacement studies, SPE 7785, 1979.
9. Pairoys F., Al-Zoukani, Nicot B. et al., Multi-physics approach for aging assessment
of carbonate rocks, SPE 149080, 2011.
10. Cuiec L., Rock/crude-oil interactions and wettability: an attempt to understand
their interrelation, SPE 13211, 1984.
11. Metodicheskie rekomendatsii po podschetu zapasov nefti i gaza ob’emnym
metodom. Otsenka kharaktera nasyshchennosti po dannym GIS
(Guidelines for the calculation of reserves of oil and gas by volumetric
method. Assessment of the nature of saturation according to well logging):
edited by Petersil’e V.I., Poroskun V.I., Yatsenko G.G., Moscow –Tver: Publ. of
VNIGNI, 2003, 260 р.
12. Vendel’shteyn B.Yu., Rezvanov R.A., Geofizicheskie metody opredeleniya
parametrov neftegazovykh kollektorov (pri podschete zapasov i proektirovanii
razrabotki mestorozhdeniy) (Geophysical methods of determining
the parameters of oil and gas reservoirs (for calculation of reserves and reservoir
engineering))., Moscow: Nedra Publ., 1978, 318 p.
13. Cuiec L.E., Restoration of the natural state of core samples, SPE 5634, 1975.
14. Gant P.L., Anderson W.G., Core cleaning for restoration of native wettability,
SPE 14875, 1988.


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