Novel approaches to core analysis

UDK: 550.8.023
DOI: 10.24887/0028-2448-2020-8-34-37
Key words: сore, soft rocks, carbonate rocks, classification, extraction, aging
Authors: I.V. Yazynina (Gubkin University, RF, Moscow), E.V. Shelyago (Gubkin University, RF, Moscow)
Standardization and methodological support of rock sample studies is an urgent task. Great part of industrial laboratory research standards was written in the last century. Current paper examines a number of methodological aspects of core studies starting with sample preparation. We should consider that the reliability of determining the reservoir properties of fractured, cavernous, unconsolidated and soft rocks is significantly lower than that of sandstone rocks due to great heterogeneity. Measurement of the porosity (static property) can be solved by increasing the accuracy of the experimental equipment, but the permeability measurement (dynamic property) requires taking into account a set of additional factors. Nowadays, laboratory specialists use a modern X-ray tomography method to assess reservoir rock properties, which allows not only to obtain initial information for heterogeneous reservoirs, but also to establish various lithological types in the petrophysical plots. It is proposed to calculate characteristics of rock heterogeneity at the scale of a single core sample. The new technique was tested for core samples from eight Russian oil fields. It is possible to classify formations with different types of pore space using only the heterogeneity characteristics, which opens up new possibilities in predicting of the oil field development.
The basic task of core studies is the picking of a representative sample collection. Statistical analysis of the X-ray tomography data performed for a number of oil deposits shows it makes no sense to standardize a collection with the same number of samples. Another issue of the core preparation process is the extraction stage. Some proposals for soft extraction in order to preserve the original wettability do not take into account the processes taking place in oil-saturated rock during well drilling and coring. The most correct way to simulate the initial natural state of the reservoir rock is the saturation of the extracted core sample with reservoir water and oil in the laboratory. However, this brings additional question about the sufficient “aging” time of the oil-saturated sample before flooding tests. Here we propose to determine aging time experimentally by measuring the electrical resistance dynamics of the core at reservoir conditions.
References
1. Yazynina I.V., Shelyago E.V., Abrosimov A.A. et al., Testing a new approach to petrophysical trend determination from X-Ray tomography (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2017, no. 2, pp. 36–40.
2. 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. 261 p.
3. Yazynina I.V., Shelyago E.V., Abrosimov A.A., Veremko N.A., Grachev N.E., Senin D.S., Novel approach to core sample MCT research for practical petrophysics problems solution (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2017, no. 1, pp. 19–23.
4. Bagrintseva K.I., Usloviya formirovaniya i svoystva karbonatnykh kollektorov nefti i gaza (Conditions for formation and properties of carbonate reservoirs of oil and gas), Moscow: Publ. RGGU, 1999, 285 p.
5. Gurbatova I.P., Kostin N.G., The scale effect in determining the reservoir properties of the reservoir in complex carbonate reservoirs (In Russ.), Neftepromyslovoe delo, 2010, no. 5, pp. 21–25.
6. Abrosimov A.A., Shelyago E.V., Yazynina I.V., Quantitative evaluation of reservoir rock heterogeneity based on X-ray computer tomography (In Russ.), Karotazhnik, 2017, no. 12(282), pp. 87–98.
7. Abrosimov A.A., Shelyago E.V., Yazynina I.V., Substantiation of a representative volume of reservoir properties data to obtain statistically reliable petrophysical relationships (In Russ.), Zapiski Gornogo instituta, 2018, V. 233, pp. 487–491.
8. Khizhnyak, G.P., Amirov A.M., Mosheva A.M. et al., Influence of wettability on oil displacement efficiency (In Russ.), Vestnik PNIPU. Geologiya. Neftegazovoe i gornoe delo = Perm Journal of Petroleum and Mining Engineering, 2013, no. 6, pp. 54–63.
9. Kovalev K., Fomkin A., Grishin P. et al., Aged carbonate cores wettability verification, SPE-182064-MS, 2016, https://doi.org/10.2118/182064-MS.
10. Gudok N.S., Bogdanovich N.N., Martynov V.G., Opredelenie fizicheskikh svoystv neftevodosoderzhashchikh porod (Determination of the physical properties of oil-and-water-containing rocks), Moscow: Nedra Publ., 2007, 592 p.
11. Kuznetsov A.M., Kuznetsov V.V., Bogdanovich N.N., On the question of preserving natural wettability of a core taken from wells (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2011, no. 1, pp. 21–23.
12. Kokorev V.I., Karpov V.B., Akhmadeysin V.I. et al., Hysteresis of relative permeabilities in water-gas stimulation of oil reservoirs (In Russ.),
SPE-171224-MS, 2014, https://doi.org/10.2118/171224-MS.
Standardization and methodological support of rock sample studies is an urgent task. Great part of industrial laboratory research standards was written in the last century. Current paper examines a number of methodological aspects of core studies starting with sample preparation. We should consider that the reliability of determining the reservoir properties of fractured, cavernous, unconsolidated and soft rocks is significantly lower than that of sandstone rocks due to great heterogeneity. Measurement of the porosity (static property) can be solved by increasing the accuracy of the experimental equipment, but the permeability measurement (dynamic property) requires taking into account a set of additional factors. Nowadays, laboratory specialists use a modern X-ray tomography method to assess reservoir rock properties, which allows not only to obtain initial information for heterogeneous reservoirs, but also to establish various lithological types in the petrophysical plots. It is proposed to calculate characteristics of rock heterogeneity at the scale of a single core sample. The new technique was tested for core samples from eight Russian oil fields. It is possible to classify formations with different types of pore space using only the heterogeneity characteristics, which opens up new possibilities in predicting of the oil field development.
The basic task of core studies is the picking of a representative sample collection. Statistical analysis of the X-ray tomography data performed for a number of oil deposits shows it makes no sense to standardize a collection with the same number of samples. Another issue of the core preparation process is the extraction stage. Some proposals for soft extraction in order to preserve the original wettability do not take into account the processes taking place in oil-saturated rock during well drilling and coring. The most correct way to simulate the initial natural state of the reservoir rock is the saturation of the extracted core sample with reservoir water and oil in the laboratory. However, this brings additional question about the sufficient “aging” time of the oil-saturated sample before flooding tests. Here we propose to determine aging time experimentally by measuring the electrical resistance dynamics of the core at reservoir conditions.
References
1. Yazynina I.V., Shelyago E.V., Abrosimov A.A. et al., Testing a new approach to petrophysical trend determination from X-Ray tomography (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2017, no. 2, pp. 36–40.
2. 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. 261 p.
3. Yazynina I.V., Shelyago E.V., Abrosimov A.A., Veremko N.A., Grachev N.E., Senin D.S., Novel approach to core sample MCT research for practical petrophysics problems solution (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2017, no. 1, pp. 19–23.
4. Bagrintseva K.I., Usloviya formirovaniya i svoystva karbonatnykh kollektorov nefti i gaza (Conditions for formation and properties of carbonate reservoirs of oil and gas), Moscow: Publ. RGGU, 1999, 285 p.
5. Gurbatova I.P., Kostin N.G., The scale effect in determining the reservoir properties of the reservoir in complex carbonate reservoirs (In Russ.), Neftepromyslovoe delo, 2010, no. 5, pp. 21–25.
6. Abrosimov A.A., Shelyago E.V., Yazynina I.V., Quantitative evaluation of reservoir rock heterogeneity based on X-ray computer tomography (In Russ.), Karotazhnik, 2017, no. 12(282), pp. 87–98.
7. Abrosimov A.A., Shelyago E.V., Yazynina I.V., Substantiation of a representative volume of reservoir properties data to obtain statistically reliable petrophysical relationships (In Russ.), Zapiski Gornogo instituta, 2018, V. 233, pp. 487–491.
8. Khizhnyak, G.P., Amirov A.M., Mosheva A.M. et al., Influence of wettability on oil displacement efficiency (In Russ.), Vestnik PNIPU. Geologiya. Neftegazovoe i gornoe delo = Perm Journal of Petroleum and Mining Engineering, 2013, no. 6, pp. 54–63.
9. Kovalev K., Fomkin A., Grishin P. et al., Aged carbonate cores wettability verification, SPE-182064-MS, 2016, https://doi.org/10.2118/182064-MS.
10. Gudok N.S., Bogdanovich N.N., Martynov V.G., Opredelenie fizicheskikh svoystv neftevodosoderzhashchikh porod (Determination of the physical properties of oil-and-water-containing rocks), Moscow: Nedra Publ., 2007, 592 p.
11. Kuznetsov A.M., Kuznetsov V.V., Bogdanovich N.N., On the question of preserving natural wettability of a core taken from wells (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2011, no. 1, pp. 21–23.
12. Kokorev V.I., Karpov V.B., Akhmadeysin V.I. et al., Hysteresis of relative permeabilities in water-gas stimulation of oil reservoirs (In Russ.),
SPE-171224-MS, 2014, https://doi.org/10.2118/171224-MS.


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