On the nitrogen content in Middle Carboniferous sediments on the territory of the Udmurt Republic

UDK: 553.98:552.578.2
DOI: 10.24887/0028-2448-2021-2-56-60
Key words: nitrogen, gas content, gas cap, deposit, field, migration, aulacogen, fault, bed
Authors: A.A. Chihirin (Izhevsk Petroleum Scientific Centre CJSC, RF, Izhevsk), V.V. Firsov (Udmurtneft JSC, RF, Izhevsk), A.V. Shostak (Izhevsk Petroleum Scientific Centre CJSC, RF, Izhevsk), K.A. Kirillov (Izhevsk Petroleum Scientific Centre CJSC, RF, Izhevsk)

The western part of the Udmurt Republic is characterized by a low degree of geological study and traditionally refers to lands with unclear prospects for oil and gas potential. One of the main constraints for further geological exploration is the presence of nitrogen gas in the Middle Carboniferous section. The article provides information on the areal distribution of the nitrogen gas zone, as well as on the general trend of changes in its content within the identified oil fields in the region. It is noted that in a number of fields with gas caps of mainly nitrogen composition, the drilling process and the implementation of geological and technical measures are significantly complicated. A comparative analysis of the nitrogen content features of the middle carboniferous section of the Kama region is carried out. In the regional plan, there is a trend of increasing nitrogen content in the western direction and its sharp increase at the latitude of the border eastern regions of Udmurtia and Tatarstan. The dependence of an increase in the nitrogen content with a decrease in the depth of oil-bearing formations is established. The formation of nitrogen gas caps is associated with the proximity of the source and migration routes of nitrogen within Udmurtia and adjacent regions. The republic's territory was graded according to the content of free and dissolved nitrogen. It is assumed that the main source of nitrogen gas is the deep-lying layer of thermobarically transformed sediments within the Kama-Belaya (Kaltasinsky) aulacogen. The gas flow to the Paleozoic floor was most intense in the zone of the western step sides of the aulacogen through the Udmurt fault system. The correlation dependence of the nitrogen content in the associated gas of the Terrigenous Devonian deposits as they approach this fault zone is established. For the territory under consideration, examples of objects that may be of interest for further search operations are given. The main prospects of the territory under consideration are associated with the study of the oil-bearing potential of the Upper Frasnian-Tournaisian carbonate deposits, as well as the Upper Devonian terrigenous deposits.


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