Research Influence оf Nitrogen оn Formation Condensate Loss During the Development оf the Chayandinskoye Field

Introduction. Currently, when calculating reserves and designing the development of oil and gas condensate fields, the priority is to achieve the highest possible and economically viable condensate recovery factor. The reservoir gas condensate system of the Chayandinskoye field, along with hydrocarbon components, contains nitrogen, carbon dioxide, and helium. To assess the effect of nitrogen on the amount of reservoir condensate loss, experimental PVT studies of recombined samples of saturated condensate and separation gas taken at the field during well testing were performed. Laboratory PVT-experiments made it possible to determine the effect of non-hydrocarbon components on the amount of condensate losses in the deposit at different temperatures and its content in methane gas. Qualitative and quantitative assessment of the effect of nitrogen (N2) on the condensate solubility in the formation gas showed that it increases the pressure of the onset of condensation and increases the loss of condensate in the deposit. The analysis of the performed studies confirmed that nitrogen affects the solubility of the condensate in gases to varying degrees and that the methane-type condensates of the Chayandinskoye field have better solubility, all other things being equal.

Materials and methods of research. The works [2-9] consider laboratory studies and analytical calculations of the fluid-dynamic properties of gas condensate mixtures in the presence of nitrogen in the system, as well as other non-hydrocarbon components that affect the loss of hydrocarbons in the deposit. At present, the effect of nitrogen on the thermodynamic properties of gas condensate systems is not sufficiently studied; therefore, it is necessary to study the effect of non-hydrocarbon components on the value of the final condensate recovery factor. For this, a set of field and laboratory studies of multicomponent systems of productive horizons of the Chayandinskoye field was carried out [2, 3]. It included field studies conducted to determine the flow rate of the separation gas, the amount of unstable condensate in the separated gas in order to calculate the condensate gas factor (cm3/m3). Laboratory studies were carried out to determine the potential content of condensate in the composition of reservoir gas, the physicochemical properties of hydrocarbons and the effect of non-hydrocarbon components on reservoir losses of condensate in the deposit [5, 6]. Field gas condensate studies were carried out by specialists from OOO Gazprom VNIIGAZ and VostSibNIIGGiMS [7]. The composition of the reservoir gas condensate system was determined based on the content and volumes of separation gas and unstable condensate sampled in the same separation mode, in which the condensate yield (CGR) was determined [8]. The calculation of the formation gas composition and determination of the potential condensate content in the formation gas were carried out in accordance with the “Methodological guide on the procedure for the development, maintenance and execution of materials to justify the potential condensate content in the formation gas and the recovery factor from the subsoil” [7]. Prediction of reservoir losses of condensate from the participation of non-hydrocarbon components in thermodynamic processes is necessary to obtain initial parameters when calculating hydrocarbons, as well as designing field development” [9].

Results and Discussion. The deposits of the Botuobinsky, Khamakinsky and Talakhsky horizons take part in the development of the Chayandinskoye field; they mutually and partially overlap each other in the northeastern part of the zone. According to the type of fluid, the deposits of the Botuobinsky horizon are gas condensate and gas condensate with oil rims. Within the license area, the deposit has been explored by 74 wells. According to the results of interpretation of geophysical well surveys, the values of effective gas-saturated thicknesses lie in the range from 0,6 m to 21,3 m. The initial formation gas composition contains (% mol): methane – 85,82-83,14; ethane – 4,45-4,77; propane – 1,11-2,67; butane fraction – 0,16-0,73; pentanes – 0,25-1,22; nitrogen – 5,62-8,11; carbon dioxide – 0,01-1,69; helium – 0,30-0,48; hydrogen - 0.00-0.08. The potential content of condensate in the formation gas is up to 35 g/m3. The density of a stable condensate under standard conditions is 0,683 g/cm3, with a molecular weight of 83 g/mol. The content of aromatic hydrocarbons is assumed to be 6,46%, naphthenic – 14,93%, methane – 78,61%. In total, nine gas deposits have been identified in the Talakh horizon. They are characterized by the average formation gas composition (% mol): methane 76,74-84,98; ethane – 3,93-5,92; propane – 1,1-1,8; butane fraction – 0,1-0,5; pentanes – 0,27-0,59. In the composition of the gas, non-hydrocarbon components are as follows (% mol): nitrogen – 6,58-16,34; carbon dioxide - up to 0,47; helium - up to 1,15 and hydrogen - up to 0,52. The potential content of the condensate is up to 32 g/m3. The content of aromatic hydrocarbons is assumed to be 6,46%, naphthenic – 14,93%, methane – 78,61%. The condensates of the productive horizons of the Chayandinskoye field are of the methane type.

Conclusion. Thus, the conducted PVT experiments to identify the effect of nitrogen and other non-hydrocarbon components in natural gas showed that the design condensate recovery factor is not significantly overestimated. The results of the experiments established the negative effect of nitrogen and carbon dioxide on reservoir losses of hydrocarbons in the deposit due to the different degree of solubility of condensate in gases (carbon dioxide improves, and nitrogen worsens their solubility). Studies of samples of separation gas and saturated condensate confirmed the data that methane-type condensates have the best solubility, other things being equal. The degree of influence of nitrogen on reservoir losses of condensate in the deposit was determined for the conditions of development of the Chayandinskoye oil and gas condensate field.

1. Antonova T.F. Fluid-bearing complexes in the Leno-Tunguska oil and gas province / T.F. Antonova, L.I. Kilina, N.V. Melnikov // Proceedings of SNIIGGiMS, 1977. Issue. 254. P. 75–79.

2. Krasnova E.I. The results of the study of the phase behavior of hydrocarbons in the presence of formation water in the gas condensate system. / E.I. Krasnova, S.I. Grachev // Academic Journal of Western Siberia, 2012. No. 4. P. 10.

3. Kontorovich V.A. Criteria for the classification of platform structures. / V.A. Kontorovich, S.Yu. Belyaev, A.E. Kontorovich // Geology, geophysics and development of oil fields, 2004. No. 1. P. 47–58.

4. Gurevich G.R. Influence of non-hydrocarbon components on the pressure value of the onset of condensation / G.R. Gurevich, I.A. Leontiev, L.Ya. Nepomniachtchi // Gas industry, 1982. No. 9. P. 23–24.

5. Leontiev I.A. Influence of various components on the pressure of the beginning of condensation of reservoir mixtures / I.A. Leontiev, L.Ya. Nepomniachtchi // in the book: Theory and practice of development of gas and gas condensate fields with low-permeability reservoirs. M., 1987. P. 109–113.

6. Krasnova E.I. Evaluation of the increase in the productivity of gas condensate wells at a late stage of field development / E.I.  Krasnova, T.D. Ostrovskaya // Akadem. Journal of Western Siberia, 2013. Vol. 9. No. 6 (49). P. 31.

7. Ostrovskaya T.D. Studies of gas condensate mixtures containing N2, H2S, CO2 / T.D. Ostrovskaya, I.A. Gritsenko // Gas industry, 1983. No. 8. P. 31–32.

8. Ostrovskaya T.D. The method of making corrections for the effect of carbon dioxide on the phase transformations of reservoir systems / T.D. Ostrovskaya, A.I. Gritsenko, V.I. Zheltovsky // Gas industry. 1988. No. 1. P. 44–45.

9. Brusilovsky A.I. Phase transformations in the development of oil and gas fields / A.I. Brusilovsky. M.: Grail, 2002. 575 p.

10. Gritsenko A.I. Nauchnye osnovy prognoza fazovogo behadve stratovykh gazokondensatsionnykh sistem [Scientific bases for predicting the phase behavior of reservoir gas condensate systems]. Gritsenko, I.A. Gritsenko, V.V. Yushkin and others. M.: Nedra, 1995. 432 p.

11. Brusilovsky A.I. Methods for calculating differential condensation of multicomponent systems / A.I. Brusilovsky // Tr. MINKH and GP named after I.M. Gubkin. 1985. Issue. 182. P. 67–77.

12. Gritsenko I.Yu. PVT - studies of the Urengoy deposit Achimov suite / I.Yu. Gritsenko, T.D. Ostrovskaya, V.V. Yushkin // Study of complex hydrocarbon systems. M.: VNIIGAZ, 2000. P. 12–15.

13. Zeinalabideen M.J., Katanova R.K., Krasnov I.I., Inyakina E.I. Study of the effect of water formation during reserves estimation and designing hydrocarbon recovery of oil and gas condensate fields. // Periodicals of Engineering and Natural Sciences, 2020. Vol. 8. No. 4. P. 2029–2034.

14. Inyakina E.I., Alsheikhly M.D.Z., Katanova R.K. Justification of condensate recovery during development of productive layers in Termokarstovoye field. // Collection: IOP Conference Series: Earth and Environmental Science. Ser. “International Science and Technology Conference “Earth Science” - Chapter 3”. 2021. P. 1–6.

15. Katanova R.K. Study of PVT-properties of gas condensate deposits in contact with residual oil / R.K. Katanova, I.I. Krasnov // In: Experience, current problems and prospects for the development of the oil and gas complex. Materials of the XI International Conference dedicated to the 40th anniversary of the TIU branch in Nizhnevartovsk. Tyumen, 2021. P. 109–112.

16. Katanova R.K., Krasnov I.I., Inyakina E.I., Alsheikhly M.D.Z. Estimation of the influence of oil flows on the formation losses of condensate during the development of multi-layer deposits. In the collection: IOP Conference Series: Earth and Environmental Science. Ser. “International Science and Technology Conference “Earth Science”, ISTC EarthScience 2022 - Chapter 1.” 2022. P. 1–9.