Comprehensive assessment and analysis of the oil and gas potential of Meso-Cenozoic sediments in the North Caucasus
Abstract
At the present stage, the development of the oil and gas industry in the Russian Federation is impossible without replenishing the raw material base, so the urgent task is to conduct investigations, prospecting and evaluation of oil and gas bearing capacity prospects in undiscovered areas. The purpose of the investigations is to analyze facies and thicknesses, choose the methodology of prospecting and exploration in reservoirs, make a comprehensive assessment of oil and gas bearing capacity prospects based on experimental investigations and construct a map of oil and gas bearing capacity prospects of the studied sediment structure. The methodology of the conducted investigations was to identify and trace zones of increased fracturing by qualitative interpretation of time seismic sections. Methods for qualitative interpretation of time seismic sections, the model of physical, chemical and geochemical criteria developed by I.A.Burlakov, gas and geochemical surveying and correlation analysis were used in the investigations. A number of prospecting criteria, established based on the analysis of reference seismic materials on well-studied areas in comparison with the results of well tests, were also used. Structural plan for forecast prospects of oil and gas bearing capacity in the studied area was made; zonal and local objects with prospects for oil and gas were identified. Graphical plotting of Eh and pH concentrations distribution and various gas and geochemical indicators allowed identifying zones of possible oil and gas accumulations and starting their detailed survey. Processing of gas and geochemical materials by means of software allowed efficient assessment of prospects for oil and gas bearing capacity of the investigated objects.
Introduction
In order to qualitatively assess oil and gas bearing capacity prospects and build a prospect map for the studied sediment structure, it was necessary to analyze facies and thicknesses and determine the specifics of the prospecting and exploration methodology in the reservoirs [12, 18].
During investigations it was required to determine the criteria for oil and gas content in Lower Maikop deposits (based on the experience of field investigations and exploration areas in Stavropol region); refine the schematic structural map of the Lower Maikop roof; analyze facies and thicknesses; determine exploration methods for clay reservoirs known in Stavropol region, based on experimental investigations; construct a prospect map for the studied sedimentary structure.
The methodology used was to identify and trace zones of increased fracturing by qualitative interpretation of temporary seismic sections. Series of search criteria (percentage content of each component in the hydrocarbon gas (HCG) series (C1-C5) and ∑HCG, Н2, О2, N2 and CO2; calculation of various oil-gas components ratios), established on the basis of analysis for reference seismic materials on well-studied areas in comparison with the results of well tests, were used. Gas and geochemical survey was also carried out.
Statement of the problem. Investigations began with processing the available geological and geophysical material for the North Caucasus [6, 24], the results of earlier seismic and drilling work, as well as research work on all promising oil and gas structures were summarized and analyzed [8, 11]. At the same time, geological and geophysical material was collected, systematized and generalized. All the information was analyzed and included in the data bank on geological and geophysical knowledge, geological structure and oil and gas bearing capacity of the territory in the North Caucasus.
At this stage comprehensive analysis of the conditions and peculiarities of oil and gas structures in the Republic of North Osetia-Alania, in addition to the analysis of all collected geological and geophysical material, included the construction of consolidated schematic structural maps for the roof of oil and gas bearing layers within the selected structures, correlation schemes of reference well sections comparison (separately by structure), thickness and lithofacies maps, lithological scheme of the study area (Fig.1) [9, 13].
During the analysis of the criteria and qualitative assessment of the oil and gas content perspectives to draw conclusions about the possible oil and gas content of the selected prospective structures, the authors were guided by the data characterizing the conditions of formation and existence of oil and gas deposits [1, 7]. It includes tectonics, stratigraphy (including palaeogeography), lithology (facies analysis and sedimentation conditions), well test data, surface oil and gas signs and gas and geochemical survey data [15, 16].
A comprehensive assessment and analysis of the oil and gas bearing capacity prospects in the Neogene structure was carried out. The site within the Nazran ledge, which is presumably associated with the bay-like spreading and wedging of the Chokrak sandstones, is the most interesting in the structural map (Fig.2) of the reflecting horizon, identified with the middle part of the Chokrak sediments. Structural constructions of two sections in the Chokrak horizon were made: the western section covering the Argudan ledge and the western part of the Osetian depression and the eastern section covering the Nazran ledge.
Oil and gas influxes were recorded in well 13 zmk (from Chokrak sediments, formation XIX, gas flow rate is 788 m3/day), well 18 zmk (blowout of clay solution and gassing with small water overflow) and well 7 (signs of hydrocarbons in basal sand layer Karagan, during testing water inflow with gas was obtained).
Methodology
The methodology of conducted research considered the identification and tracing of zones with increased fracturing by qualitative interpretation of temporary seismic sections [5, 20, 22]. At the same time, a number of search criteria (percentages of each component in the series of HCG (C1-C5) and ∑HCG, H2, O2, N2 and CO2; calculation of ratios for various oil and gas components), established based on the analysis of reference seismic materials from well-studied areas in comparison with the results of well tests, were used. If the recording is of good quality, zones of oil-prospecting interest can be identified [19, 21]. The scheme for propagation of fracture-dispersed zones over an area is constructed by correlating [28, 35] the same-type signs of wave field disturbance from profile to profile, although this procedure is associated with great difficulty in selecting a reference correlation variant.
Discussion
Computer processing of data obtained by analysis of oil and gas components and Eh-, pH-metry of rocks (including calculation of background field of oil and gas components for the object) [10, 17]; calculation of oil and gas components contrast values for each sampling point; determination of percentages for each component in the series of HCG (C1-C5) and ∑HCG, H2, O2, N2 and CO2; calculation of ratios for various oil and gas components; graphical plotting of distributions for each oil and gas component, for Eh and pH, for ratios of oil and gas components and their contrasts with regional and local backgrounds, as well as for changes in tangent values and rank correlation coefficients, reflecting zones of oil and gas accumulations and deep water unloading along the profiles of the studied area. Physical, chemical and geochemical criteria for local prediction of oil-saturated reservoirs in the Neogene structure are shown in table [3, 17, 27].
Comprehensive analysis of oil and gas components (comparing them with each other) [2, 14] was carried out using the contrast curves of the HCGads components relative to the calculated background for the investigated object.
Comparison for the distribution of gas concentrations by individual gas vapours (close in concentration levels) revealed their uniformity and marked differences in distribution along the profile line, indicating possible differences in their genesis.
Gas and geochemical investigations along the meridional profile A-B (Fig.3) showed that structures with supposed and established oil and gas content occur along the A-B profile line, which are not sharply distinguished from the background field by levels of HCGads concentrations, but are reflected in features of HCGads composition (naphthenic gas type) and individual gas and geochemical indicators [30, 31]. Abnormal values of HCGads are manifested in the investigated area at points 1, 4, 24, 25, reaching values of HCGads concentrations of about 0.12 cm3/kg, while points with values of about 0.07 cm3/kg are also noted in this area (Fig.4).
Physical, chemical and geochemical criteria for local prediction of oil-saturated reservoirs in the Neogene structure
Parameters |
Non-reservoir |
Reservoir |
Open porosity, % |
< 10.5 |
>10.5 |
Volumetric mass, g/cm3 |
> 2.4 |
< 2.4 |
Lime content, % |
> 8-10 |
0-4 |
Pseudofracture number, m–1 |
0-500 |
1500-4000 |
HB content, % |
< 0.5 |
> 0.5 |
HB content in open cavities, % |
< 0.2 |
> 0.2 |
Bitumen content HB+DSBB, % |
< 0.1-0.8 |
> 0.8 |
Redox potential Еh, mV |
>70 |
< 40 |
Hydrophobicity coefficient Кhpb, units |
> 0.17 |
< 0.17 |
Diffusion-adsorption activity, mV |
> 35 |
30-35 |
Cation exchange capacity Q, mg eqv/100 g |
12.5-22.0 |
4.2-8.1 |
К+Nа+/Са+Мg2+ |
>1.0 |
< 1.0 |
Luminescence |
A very faint disappearing ring of light blue colour |
Spot of intense light blue |
Colour of the hydrocarbon extract |
Colourless to the eye, light blue under the luminescope |
Light straw to brown in colour to the eye, intensely blue to dark blue under the luminescope |
In addition to these abnormal HCGads manifestations, the A-B profile line also highlights more contrasting anomalies in the southern part of the profile (points 4-7) and at its northern end (points 31-34), but these HCGads anomalies are characterized by deep water unloading type gases with an elevated gas-oil ratio.
In terms of the methane percentage in the HCG, the A-B profile line is dominated by relatively light gases (CH4 is about 20 %), the HCGads percentage in the sum of all oil and gas components (% HCG of ∑G) is low. This is due to the very high total share of carbon dioxide (CO2 is about 99 %). In addition, H2ads is almost an order of magnitude higher than the HCGads on the A-B profile line, even in the areas of oil and gas field expansion [33, 34]. In the mountain-foothill areas H2 and CO2 are more actively supplied from the depths because the upward migration routes along the section are more favorable there (presence of a deep fault along the Terek river bed). Therefore, more active inflow of gases from deep zones of the Earth crust occurs along the deep fault, also connected with unloading of waters with increased gas-oil ratio.
Fig.3 shows sharp changes in Eh and pH in the southern part of the profile and their smooth expansion in the northern part. For the southern zones of the profile, which are located closer to the mountains, a sharp decrease in pH values (up to 5-6), i.e. with the release of an acid environment, is characteristic. Presumably, it is connected with the fact that rock fracturing and fracture tectonics are more active closer to the mountains, contributing to powerful inflows of deep gases and formation of additional CO2. Indeed, at points 3-8, there is a sharp decrease in pH, an increase in redox potential Eh (50-200 mV), and increase in concentrations of CO2, HCG, and, to a lesser degree, H2. The composition of HCG is the heaviest here (CH4 about 15 %). Next to this zone at points 8, 7, 12, 17 the HCG composition is much lighter (CH4 25-30 %). The general tendency for lightening of HCGads (increase of CH4 share in ∑HCG) from south to north in southern part of A-B profile can be a ground for assumption about tectonogenesis activity near mountainous areas. On the right bank of the Terek river there is a general decrease in the concentrations of all gases and development of consistently high (about 8.5) pH values with Eh around 50 mV. In the smooth background field of gases, there is only a particular increase in concentrations of HCGads, H2ads and CO2ads associated with oil manifestations in the study area. The naphthic type of gases, characteristic for areas with oil and gas accumulations, is also observed here. Only in this part of the A-B profile there are sampling points with naphthic manifestation of CH4 and HCG coefficients, when a decrease of CH4 coefficient values is observed with an increase of HCG coefficient values. This is due to the fact that when the background field is disturbed by gases from oil and gas accumulations, the share of HCG in the sum of the investigated gases increases, while the composition of HCG becomes heavier (the share of CH4 decreases). The points with naphthic type of gas (tendency of increase of contrast of components of HCGads from light to heavy homologues of methane) are fixed within the limits of development of oil-and-gas bearing capacity of the investigated territory with the help of a contrast curve for HCGads components (Fig.4). The southern part of the profile A-B is characterized by the manifestations of gases of the water unloading type with an increased gas-oil ratio (points 1, 6, 8, 10), when the contrast curves of the HCGads components show a trend of increasing contrast from heavy to light homologues of methane [25, 26].
Thus, the A-B (south-north) submeridional profile line shows zones of intense water unloading with an elevated gas-oil ratio in the southern part and low levels of gas concentrations in the middle part with individual manifestations of high gas concentrations within the spread of oil and gas areas. There is a marked increase in gas concentrations in the northern part of the A-B profile, which may be related to approaching the oil and gas bearing structure [23, 32].
The established level of the calculated background gases for the study area by points of the meridional gas and geochemical profile A-B belongs to the category of reduced values of HCGads concentrations of (0.08 cm3/kg), H2ads (1.2 cm3/kg) and CO2ads (232 cm3/kg). The background pH values are about 8 and Eh is about 50 mV.
Conclusion
The following results were obtained in the research:
- criteria for the oil and gas content of Lower Maikop sediments (in the fields and exploration areas of the North Caucasus) are defined;
- schematic structural map of the Lower Maikop roof is refined;
- facies and thicknesses are analyzed;
- specifics of prospecting and exploration in reservoirs are defined (based on research known in the North Caucasus);
- comprehensive assessment of the oil and gas potential and a structural plan of the oil and gas bearing capacity of the study area was made [27, 29].
The conducted analysis for distribution of hydrogen sulfide content in dissolved gas at oil deposits of Valanginian-Berrias in a part of the investigated territory and beyond its limits has revealed the increase of hydrogen sulfide concentration in formation fluids with depth increase of sulfate-bearing rocks. It is clearly traced in the direction from sides of Tersko-Caspian foredeep to its most submerged part where hydrogen sulfide content in Valanginian-Berrias sediments reaches 8 %.
Investigations showed that the background concentrations of the gas field in the study area are characterized by a low level. On a submeridianal profile A-B fluctuations of background concentrations of HCGads are 0.08-0.12 cm3/kg, for the sublatitudinal profile C-D (see fig. 3) these fluctuations reach 0.16-0.26 cm3/kg, which is a favorable factor for identification of objects with oil and gas accumulations.
Graphic plotting of Eh and pH concentrations and various gas and geochemical indicators allowed to identifyzones of possible of oil and gas accumulations and to start their detailed survey (Fig.5). Processing of gas and geochemical materials by means of applied software, made it possible to unbiasedly estimate the prospects for oil and gas bearing capacity of investigated objects.
The authors would like to thank D.G.Petrakov, V.V.Maier, R.R.Gogichev for their help and support in the organizational, research and experimental work at the study areas.
References
- Bembel R.M., Sukhov L.A., Shchetinin I.A. Ways of increasing geological efficiency of hydrocarbon fields development in western Siberia. Oil and Gas Studies. 2017. N 6, p. 6-10. DOI: 10.31660/0445-0108-2017-6-6-10 (in Russian).
- Bosikov I.I., Klyuev R.V., Gavrina O.A. Analysis of geological-geophysical materials and qualitative assessment of the oil and gas perspectives of the Yuzhno-Kharbizhinsky area (Northern Caucasus). Geology and Geophysics of Russian South. 2021. Vol. 11. N 1, p. 6-21. DOI: 10.46698/VNC.2021.36.47.001 (in Russian).
- Bosikov I.I., Mazko A.I., Maier A.V.A comprehensive evaluation of the productive formation collector of the Kanevskoye field. Oil and gas studies. 2021. N 3, p. 25-36. DOI: 10.31660/0445-0108-2021-3-25-36 (in Russian).
- Bosikov I.I., Klyuev R.V., Egorova E.V. Assessment of oil and gas potential prospects of the North Eastern unit of the South Khulym deposit. Sustainable Development of Mountain Territories. 2019. Vol. 11. N 1 (39), p. 7-14.DOI: 10.21177/1998-4502-2019-11-1-7-14 (in Russian).
- Bronskova E.I. Comprehensive analysis of April field geological structure to provide effective additional exploration and development of Tyumen suite deposits. Geology, Geophysics and Development of Oil and Gas Fields. 2016. N 8, p. 36-44 (in Russian). URL: http://www.vniioeng.ru/_user_files/file/ants/ge/Geology_Geophysics_2016-08_rus.htm#Bookmark06
- Gaiduk V.V. The nature of the oil and gas potential of the tersko-sunzhensky oiland gas-bearing region. Geology, geophysics and development of oil and gas fields. 2019. N 2, p. 40-46. DOI: 10.30713/2413-5011-2019-2-40-46 (in Russian).
- Danilov V.N. Formation of thrusts and hydrocarbon potential of Urals foredeep. Oil and gas geology. 2021. N 1, p. 57-72. DOI: 10.31087/0016-7894-2021-1-57-72 (in Russian).
- Dzhafarov R.R., Ragimov F.V., Gashimova G.I. Prospects for oil and gas bearing capacity of the Nadkirmaki clay suite of the Chilov field. Azerbaidzhanskoe neftyanoe khozyaistvo. 2020. N 12, p. 12-16. DOI: 10.37474/0365-8554/2020-12-12-16 (in Russian).
- Ivlev D.A. Method for regional forecast of oil and gas potential territories by machine learning algorithms on the example of the Tyumen formation of western Siberia. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering. 2021. Vol. 332. N 1, p. 41-53. DOI: 10.18799/24131830/2021/1/2998 (in Russian).
- Makridin E.V., Tyulenev M.A., Markov S.O. et al. Using waste rock to improve the environmental safety of the coal mining region. Gornyi informatsionno-analiticheskii byulleten. 2020. N 12, p. 89-102. DOI: 10.25018/0236-1493-2020-12-0-89-102 (in Russian).
- Kaukenova A.S. Oil and gas potential of the south Turgay basin. Proceedings of higher educational establishments. Geology and Exploration. 2020. N 3, p. 38-45. DOI: 10.32454/0016-7762-2020-63-3-38-45 (in Russian).
- Kobylinskii D.A. Criteria for determining the oil and gas potential of the territory based on the data of ground geochemical survey performed on the ground and artificial sorbent. The Eurasian Scientific Journal. 2020. Vol. 12. N 6. N 51NZVN620. URL: https://esj.today/PDF/51NZVN620.pdf
- Kovalenko I.V., Sokhoshko S.K. Modelling the development of multi-layered oil rims. Izvestiya vysshikh uchebnykh zavedenii. Neft i gaz. 2018. N 3, p. 50-54. DOI: 10.31660/0445-0108-2018-3-50-54 (in Russian).
- Klyuev R.V., Bosikov I.I., Maier A.V., Gavrina O.A. Comprehensive analysis of the effective technologies application to increase sustainable development of the natural-technical system. Sustainable Development of Mountain Territories. 2020. Vol. 12. N 2 (44), p. 283-290. DOI: 10.21177/1998-4502-2020-12-2-283-290 (in Russian).
- Bosikov I.I., Mazko A.I., Maier A.V., Gagarina O.V. A comprehensive analysis of conditions and features of oil-and-gas content within the Akhlovskaya structural zone (the North Caucasus). Oil and gas studies. 2021. N 2, p. 25-38. DOI: 10.31660/0445-0108-2021-2-25-38 (in Russian).
- Kuznetsov V.G., Zhuravleva L.M. Reef formations in the west Canada basin and their oil and gas potential. Lithology and Mineral Resources. 2018. Vol. 53. N 3, p. 236-251. DOI: 10.1134/S0024490218030045
- Egorova E.V., Klyuev R.V., Bosikov I.I., Tsidaev B.S. Assessing the use of effective technologies to enhance the sustainable development of the natural and technical system of the oil and gas industry. Ustoichivoe razvitie gornykh territorii. 2018. Vol. 10. N 3 (37), p. 392-403.
- Gainanshin R.N., Khafizov S.F., Abramov V.Yu. et al. Oil and Gas Perspective Assessment and the Choice of the Exploration Program based on the Multivariate Geological Modeling. Oil and Gas Territory. 2019. N 3, p. 12-16 (in Russian). URL: https://tng.elpub.ru/jour/article/view/866
- Panikarovskii E.V., Panikarovskii V.V., AnashkinaA.E. Vankor oil field development experience. Oil and gas studies. 2019. N 1, p. 47-51. DOI: 10.31660/0445-0108-2019-1-47-51 (in Russian).
- Sharafutdinov V.F., Cherkashin V.I., Musikhin V.A. et al. Prospects of oil and gas production of michael deposits of buy-naks depression of pre-degrenary Dagestan. Trudy Instituta geologii Dagestanskogo nauchnogo tsentra RAN. 2018. N 1 (72), p. 17-23. DOI: 10.31161/2541-9684-2018-62-1-17-23 (in Russian).
- Sevostyanova R.F., Sitnikov V.S. The development of ideas about the structure and oil and gas potential of nepa-botuoba anteclise and adjacent part of predpatomskii trough. Journal of Mining Institute. 2018. Vol. 234, p. 599-603. DOI: 10.31897/PMI.2018.6.599
- Cherkashin V.I., Sabanaev K.A., Gadzhieva T.R. et al. Tectonic structure and oil and gas bearing capacity of the sedimentary cover of the Caspian Sea bed. Trudy Instituta geologii Dagestanskogo nauchnogo tsentra RAN. 2018. N 4 (75), p. 24-29. DOI: 10.31161/2541-9684-2018-62-4-25-30 (in Russian).
- Katsubin A.V., Khoreshok A.A., Tyulenev M.A., Markov S.O. Technology for advance excavation of inclined and steep coal seams with hydraulic backhoes. Gornyi informatsionno-analiticheskii byulleten. 2020. N 11, p. 27-36. DOI: 10.25018/0236-1493-2020-11-0-27-36 (in Russian).
- Ulmasvai F.S., Dobrynina S.A., Sidorchuk E.A. New regularities in the distribution of oil and gas in sedimentary stratum (by the case of Ciscaucasia). Actual Problems of Oil and Gas. 2018. Iss. 1 (20). N 8. DOI: 10.29222/ipng.2078-5712.2018-20.art8 (in Russian).
- De Oliveira D.M., Sobral L.G.S., Olson G.J., Olson S.B. Acid leaching of a copper ore by sulphur-oxidizing microorganisms. Hydrometallurgy. 2014. Vol. 147-148, p. 223-227. DOI: 10.1016/j.hydromet.2014.05.019
- Doifode S.K., Matani A.G. Effective Industrial Waste Utilization Technologies towards Cleaner Environment. International Journal of Chemical and Physical Sciences. 2015. Vol. 4. Special Issue – NCSC, p. 536-540. URL: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.680.646&rep=rep1&type=pdf
- Melnikov N.N., Kalashnik A.I., Kalashnik N.A., Zaporozhets D.V. Integrated Multi-Level Geomonitoring of Natural-and-Technical Objects in the Mining Industry. Journal of Mining Science. 2018. Vol. 54. P. 535-540. DOI: 10.1134/S1062739118043977
- 28. Litvinenko V.S. Digital Economy as a Factor in the Technological Development of the Mineral Sector. Natural Resources Research. 2020. Vol. 29, p. 1521-1541. DOI: 10.1007/s11053-019-09568-4
- Petrov Yu.S., Sokolov A.A. Increase of effective management of technological processes of the mountain enterprise on the basis of the analysis of information on technogenic cycles. 2nd International Conference on Industrial Engineering, Applications and Manufacturing (ICIEAM), 19-20 May 2016, Chelyabinsk, Russia. IEEE, 2016, p. 1-5. DOI: 10.1109/ICIEAM.2016.7911691
- Rylnikova M.V., Vladimirov D.Y., Pytalev I.A., Popova T.M. Robotic Geotechnologies as a Way to Increase Efficiency and Greening the Development of Mineral Resources. Physical and Technical Problems of Mining. 2017. Vol. 53, p. 84-91. DOI: 10.1134/S1062739117011884
- Sinclair L., Thompson J. In situ leaching of copper: Challenges and future prospects. Hydrometallurgy. 2015. Vol. 157. Р. 306-324. DOI: 10.1016/j.hydromet.2015.08.022
- Zhengfu Bian, Xiexing Miao, Shaogang Lei et al. The challenges of reusing mining and mineral processing wastes. Science. 2012. Vol. 337. Iss. 6095, p. 702-703. DOI: 10.1126/science.1224757
- Zhukovskiy Yu.L., Korolev N.A., Babanova I.S., Boikov A.V. The probability estimate of the defects of the asynchronous motors based on the complex method of diagnostics. Innovations and prospects of development of mining machinery and electrical engineering. IOP Conference Series: Earth and Environmental Science. 2017. Vol. 87. Iss. 3. N 032055. DOI: 10.1088/1755-1315/87/3/032055
- Vrancken C., Longhurst P.J., Wagland S.T. Critical review of real-time methods for solid waste characterization: Informing material recovery and fuel production. Waste Management. 2017. Vol. 61, p. 40-57. DOI: 10.1016/j.wasman.2017.01.019
- Zhukovskiy Y., Koteleva N. Diagnostics and evaluation of the residual life of an induction motor according to energy parameters. Mechanical Science and Technology Update (MSTU-2018), 27-28 February 2018, Omsk, Russia. Journal of Physics: Conference Series, 2018. Vol. 1050. N 012106. DOI: 10.1088/1742-6596/1050/1/012106