Geological Structure and Oil Potential of the Pervomayskoye Field
Abstract Generated abstract
The paper describes the geological setting and petroleum potential of the Pervomayskoye field in Tomsk Oblast, located on a local uplift in the northeastern Novo-Vasyugan swell of the Kaimysov arch. Based on seismic structural interpretation and early exploratory drilling, it identifies Late Jurassic Vasyugan Formation sandstones and siltstones, especially bed Yu-1, as the main productive interval, with the discovery well yielding water-free oil at 57.5 cubic meters per day. The author concludes that the field is likely small but commercially significant, requiring further drilling to define pool boundaries, oil-bearing interval, and reservoir regime, and notes that Cretaceous deposits also merit careful evaluation in light of nearby discoveries.
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GEOLOGICAL STRUCTURE AND OIL POTENTIAL OF THE PERVOMAYSKOYE FIELD
Yu. V. Naidanov
(Presented by Professor A. V. Aksarin)
The Pervomayskoye oil field was discovered in 1969 and is located in the Kargasok District of Tomsk Oblast. In tectonic terms, the field is confined to the local uplift of the same name, identified by areal seismic surveying in 1963–1964 in the northeastern part of the Novo-Vasyugan swell, which in turn is situated in the central part of the Kaimysov arch. The Pervomayskoye uplift (structure), along the reference reflecting horizon II-a (the base of the Maryanovka Formation), has a northwestern strike and is outlined by the seismic isohypse of −2,500 m. Its dimensions within this isoline are 15 × 4 km, and its amplitude is 100–120 m. Along the −2,460 m isohypse, the structure is complicated by two domes located along the long axis (Fig. 1).
The first oil fields on the territory of the Kaimysov arch were discovered in 1964 (Moiseevskoye, Lontyn-Yakhskoye), which are located in the southern and central parts of the arch; in 1965 and 1967 two more fields were added in the north of the arch. Finally, the latest of those discovered—Pervomayskoye—is located between two fields: Lontyn-Yakhskoye to the south and Katylginskoye to the north. Such proximity, in combination with other favorable exploration criteria (height of the structure, its area, etc.), long ago placed the Pervomayskoye structure among the most promising and highest-priority targets for exploratory drilling. And indeed, the very first well drilled on the southeastern dome, well No. 260, penetrated an oil pool in Jurassic deposits and became the discovery well of the field.
Paleozoic, Mesozoic, and Cenozoic deposits take part in the geological structure of the Pervomayskoye field. The oil-bearing rocks proved to be sandstones and siltstones of the Vasyugan Formation of Late Jurassic age. The main productive bed is bed Yu-1, which was penetrated in the depth interval of 2,444–2,472.8 m. The total thickness of the bed is 28.8 m, the effective thickness is 10.4 m, and the oil-saturated thickness is 7.6 m. During testing of its upper part in the interval 2,453–2,442 m, a flowing stream of water-free oil was obtained at a rate of 57.5 m³/day through an 8-mm choke. The lower part of the bed has not been tested; therefore the oil-water contact can be drawn only conditionally along the lower perforation holes. However, judging by the size of the structure, its height, the total and effective thicknesses of the bed, and the results of testing, the field will tentatively be small. At present, the Pervomayskoye field is being explored by deep drilling. It is necessary to establish the boundaries of the oil ԥ
Figure 1. Structural map of the Pervomayskoye field: 1—isochrones of the reference reflecting horizon II-a; 2—drilled wells.
the pool, the oil-bearing stage, and determine the field’s regime. The oil of the Pervomayskoye field is light, with a specific gravity of 0.837 g/cm³ and an initial boiling point of 48°C. The content of light fractions boiling off up to 200° is 38.8%; the oil is low-sulfur—0.69%. Its viscosity under surface conditions is 4.8 cSt.
In connection with the discovery of commercial oil potential in the Cretaceous deposits on the South Cheremshanskaya area (east of the Kaymysov arch), their prospects are increased both for the Kaymysov arch as a whole and for the Pervomayskaya area. Therefore, these deposits should be studied carefully. Provision should be made for core sampling, formation testing with a formation tester during drilling, etc.