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Structural phase transition and necessity to consider this phenomenon in projects of heavy oil fields development

UDK: 665.61.035.6
DOI: 10.24887/0028-2448-2018-7-32-34
Key words: phase transition temperature, rheology, waterflooding, heavy oil
Authors: A.Kh. Kabirova (TatNIPIneft, RF, Bugulma), V.M. Khusainov (TatNIPIneft, RF, Bugulma)

The paper discusses the problem of structural transition of heavy oil found in Carboniferous reservoirs–the strategic reserve of the Republic of Tatarstan. Heavy oil is characterized by increased concentration of high-molecular compounds (asphaltenes, resins, paraffin) and by high viscosity (30-200 mPa·s). Because of various physical and chemical processes and change of thermodynamic in-situ conditions, rheological properties of oil change at all stages of the oil extraction process. Considering that temperature is the critical parameter that controls oil viscosity, yield strength, pour point, wax crystallization and precipitation, knowledge of the relationship between the temperature and the rheological properties of oil is very important for planning of reservoir management operations. Selection of the efficient field development strategy and production enhancement methods seems impossible without knowledge about phase transition temperature in reservoirs with in-situ temperature approximating to the transition temperature. For the purpose of this study, the transition temperature was calculated by the indirect method from viscosity vs. temperature relationships and the following approximation of the exponent for solid-like and liquid-like states. The exponents’ crossing is the point (temperature) of phase transition. For laboratory research, we used the rotary rheometer RHEOTEST RN 4.1. Oil rheological properties were determined for the temperature range from 1°C to 40°C, effective viscosity for each temperature value was determined for the range from 1 to 60 s-1.


The Volga-Ural petroleum basin fields developed by waterflooding were targets of our research. Changes
of transition temperature and concentrations of asphaltenes and resins occurring in-situ in the process of oil reserves development are shown. It was found that in oil fields developed by waterflooding, the transition temperature tends to increase and approximates to the original in-situ temperature, which might result in decrease of the amount of produced oil.

References

1. Zlobin A.A., Analysis of phase transitions in the pore space paraffin reservoir rocks (In Russ.), Vestnik Permskogo natsional'nogo issledovatel'skogo politekhnicheskogo universiteta. Geologiya. Neftegazovoe i gornoe delo = Perm Journal of Petroleum and Mining Engineering, 2012, no. 5, pp. 47-56.

2. Iktisanov V.A., Sakhabutdinov K.G., Rheological studies of paraffin-base oil at different temperatures (In Russ.), Kolloidnyy zhurnal = Colloid Journal, 1999, V. 61, no. 6, pp. 776-779.

3. Khusainov V.M., Struktura ostatochnykh zapasov Tatarstana. Problemy i perspektivy razrabotki (Structure of residual reserves of Tatarstan. Problems and prospects of development), Collected papers “Trudnoizvlekaemye i netraditsionnye zapasy uglevodorodov: opyt i prognozy” (Hard-to-recover and unconventional hydrocarbon reserves: experiences and forecasts), Proceedings of International scientific and practical conference, Kazan’: Fen Publ., 2014, 2014. – S. 86-89.

4. Kur'yakov V.N., Issledovanie fazovykh prevrashcheniy v uglevodorodnykh flyuidakh metodom staticheskogo i dinamicheskogo rasseyaniya sveta (Investigation of phase transformations in hydrocarbon fluids using static and dynamic light scattering): thesis of candidate of physical and mathematical sciences, Moscow, 2016.

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The paper discusses the problem of structural transition of heavy oil found in Carboniferous reservoirs–the strategic reserve of the Republic of Tatarstan. Heavy oil is characterized by increased concentration of high-molecular compounds (asphaltenes, resins, paraffin) and by high viscosity (30-200 mPa·s). Because of various physical and chemical processes and change of thermodynamic in-situ conditions, rheological properties of oil change at all stages of the oil extraction process. Considering that temperature is the critical parameter that controls oil viscosity, yield strength, pour point, wax crystallization and precipitation, knowledge of the relationship between the temperature and the rheological properties of oil is very important for planning of reservoir management operations. Selection of the efficient field development strategy and production enhancement methods seems impossible without knowledge about phase transition temperature in reservoirs with in-situ temperature approximating to the transition temperature. For the purpose of this study, the transition temperature was calculated by the indirect method from viscosity vs. temperature relationships and the following approximation of the exponent for solid-like and liquid-like states. The exponents’ crossing is the point (temperature) of phase transition. For laboratory research, we used the rotary rheometer RHEOTEST RN 4.1. Oil rheological properties were determined for the temperature range from 1°C to 40°C, effective viscosity for each temperature value was determined for the range from 1 to 60 s-1.


The Volga-Ural petroleum basin fields developed by waterflooding were targets of our research. Changes
of transition temperature and concentrations of asphaltenes and resins occurring in-situ in the process of oil reserves development are shown. It was found that in oil fields developed by waterflooding, the transition temperature tends to increase and approximates to the original in-situ temperature, which might result in decrease of the amount of produced oil.

References

1. Zlobin A.A., Analysis of phase transitions in the pore space paraffin reservoir rocks (In Russ.), Vestnik Permskogo natsional'nogo issledovatel'skogo politekhnicheskogo universiteta. Geologiya. Neftegazovoe i gornoe delo = Perm Journal of Petroleum and Mining Engineering, 2012, no. 5, pp. 47-56.

2. Iktisanov V.A., Sakhabutdinov K.G., Rheological studies of paraffin-base oil at different temperatures (In Russ.), Kolloidnyy zhurnal = Colloid Journal, 1999, V. 61, no. 6, pp. 776-779.

3. Khusainov V.M., Struktura ostatochnykh zapasov Tatarstana. Problemy i perspektivy razrabotki (Structure of residual reserves of Tatarstan. Problems and prospects of development), Collected papers “Trudnoizvlekaemye i netraditsionnye zapasy uglevodorodov: opyt i prognozy” (Hard-to-recover and unconventional hydrocarbon reserves: experiences and forecasts), Proceedings of International scientific and practical conference, Kazan’: Fen Publ., 2014, 2014. – S. 86-89.

4. Kur'yakov V.N., Issledovanie fazovykh prevrashcheniy v uglevodorodnykh flyuidakh metodom staticheskogo i dinamicheskogo rasseyaniya sveta (Investigation of phase transformations in hydrocarbon fluids using static and dynamic light scattering): thesis of candidate of physical and mathematical sciences, Moscow, 2016.

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