PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
NAMED AFTER S. M. KIROV, HOLDER OF THE ORDER OF THE OCTOBER REVOLUTION
AND THE ORDER OF THE RED BANNER OF LABOR

Volume 254 1975

ON THE NECESSITY OF SYSTEMATIC PROSPECTING FOR LITHOLOGICAL GAS AND GAS-CONDENSATE POOLS IN THE SOUTHERN PART OF TOMSK OBLAST, AS EXEMPLIFIED BY THE DISCOVERY OF THE OSTANINO FIELD

V. G. CHERTENKOV

(Presented by Professor A. V. Aksarin)

At one time the author wrote about the prospects of the southern part of Tomsk Oblast, including the western slope of the Pudin arch, for finding lithological oil and gas pools there [1]. A specific area was indicated, in particular, the Ostanino structure (Fig. 1).

Deep exploratory drilling carried out in recent years in this area confirmed the stated assumption. Thus, during the drilling of the Ostanino and Mirnaya structures, four gas-condensate lithological pools were discovered, forming the Ostanino field. The field is located in the northwestern part of the uplift of the same name, which is dome-shaped. Administratively, it is situated on the territory of Kargasok District, Tomsk Oblast.

Along reflecting horizon II-a, confined to the base of the Maryanovka Suite of the Upper Jurassic, the field is outlined as two separate structures: Ostanino and Mirnaya, situated next to one another (Fig. 2). Hypsometrically they are at the same level and are contoured by the seismic isohypse of −2400 m, having, respectively, dimensions along it of \(14 \times 11\) km and \(20 \times 7\) km. The structures are separated from one another by a small saddle.

Deep exploratory drilling carried out recently on these structures has shown that, as a result of changes in lithology and deterioration of the reservoir properties of the beds from west to east, seismic horizon II-a does not coincide in depth with the base of the Maryanovka Suite, to which it is usually confined, but seems to slip—

Fig. 1. Structural map of the Ostanino field: 1—structure contours based on drilling, 2—drilled wells, 3—projected wells, 4—seismic contours of horizon Pa, 5—OWC of bed Yu-1, 6—numerator: well number; denominator: absolute elevation of the top of bed Yu-1, I—Ostanino, II—Mirnoe

...position of the seismic horizon along beds with identical lithological and reflecting properties, as a result of which seismic horizon II-a intersects the section with respect to depths (Fig. 2). As a result, the structural map for the top of bed Yu-1 (the base of the Maryanovka suite (Fig. 2)) does not coincide with seismic horizon II-a to a rather significant extent. According to preliminary data from deep exploratory drilling, it may be said—

Fig. 2. Geological section along line 1—1. 1—sandstones, 2—argillites, 3—seismic horizon Pa, 4—testing interval, 5—flow rates

Results of well testing
Table 1

It may be said that the Ostanino and Mirnaya structures along the top of bed Yu-1 are a single structure complicated by three small domes. On the structural map these two structures merge into one and are contoured by the \(-2440\)-meter isohypse (Fig. 1).

Thus, exploration work has established that the two gas-condensate fields, Ostanino and Mirnoye, are in fact one, larger Ostanino field. The field is multilayered (beds Yu-I, Yu-II, Yu-III, Yu-IV). Commercial gas content has so far been proved by testing only in bed Yu-1 (the top part of the Vasyugan suite); however, judging from BKZ materials, bed Yu-II is also gas-saturated. During testing of beds Yu-III and Yu-IV, oil, condensate, and a small quantity of gas were obtained. Apparently, these beds contain an oil fringe.

All the beds, and especially Yu-III and Yu-IV, are facies-variable and are represented in the west by sandstones that pass eastward into siltstones and argillites. In the same direction the permeability of the beds deteriorates, which is especially evident from well flow rates (Table 1).

Each bed forms an independent pool with its own water contact. According to the results of well testing and BKZ processing materials, in beds Yu-1 and Yu-II the GWC is conditionally placed at the elevation of \(2420\) m, while for beds Yu-III and Yu-IV the OWC is placed somewhat lower, at the elevation of \(2435\) m.

The improvement of the reservoir properties of the beds westward, toward the Nyurolka depression, suggests the possibility of finding lithologic-type traps throughout the entire southwestern termination of the Pudino arch. Particular attention should be paid to the structures and structural flexures located west of the Ostanino area: the Nizhne-Tabagan structure, the Verkhne-Armiya flexure, and the Mirno-Ozerny flexure. Although these structures, with respect to reflecting horizon II-a, will probably lie hypsometrically somewhat lower than Ostanino, this should not be an obstacle to putting them into drilling, since it is precisely here that there are zones of wedging out and lithologic replacement of the coarse-grained sandstones of the Tyumen, Vasyugan (and perhaps also Kulomzino) suites, overlain by sufficiently thick seals.

Of similar interest are the structures located on the Vodorazdelnoye dome-shaped uplift: Vodorazdelnaya, Verkhne-Vasyuganskaya, and Chagvinskaya. Along with structural traps, there will undoubtedly be traps here of lithologic, structural-lithologic, and perhaps also tectonic types, containing gas or gas-condensate pools.

REFERENCES

1. V. G. Chertenkov, L. S. Babikova. Prospects for searching for lithologic oil and gas pools in the southern part of Tomsk Oblast, using bed B-X of the Myldzhino field as an example.—“Izv. TPI,” vol. 216, 1971.