The Usinskoye field has been operating since 1977. Its development is carried out in very difficult geological conditions associated with the features of the deposit. Formation fluid is a difficult-to-recover fluid, as it has an abnormally high viscosity. However, high viscosity oils in recent decades are considered as the main reserve of world production. According to various estimates, their reserves in Russia range from 30 to 75 billion tons, and most of them are located in the Volga-Ural region. Therefore, the introduction of enhanced oil recovery technologies for such formations has gained particular relevance.
Where is the Usinsk deposit located?
The Usinsk oil deposit is located in the northeast of the homonymous region of the Komi Republic. Its area covers the Pechora lowland and the Kolva river basin (the right tributary of the river Usa). The nearest city is Usinsk. The location of the Usinsky Lukoil oil field is associated with the transitional natural zone from the tundra to the taiga. The climate here is sharply continental, with an average annual temperature of -25 ° C. In winter, the thermometer drops to -55 ° C. The relief of this area is a low-lying, very marshy plain with elevated hilly areas.
Transport communications include rail, river navigation, and helicopter delivery. The Vozey-Yaroslavl oil pipeline was laid across the territory.
There is also a deposit with a similar name - the Malo-Usinskoye field, which is located in the south of the Elovsky district, in the Perm region, near the village of Malaya Usa. It is associated with the Devonian and Lower Middle Visean strata.
Short description
This field is confined to the Timan-Pechersk oil and gas basin, which is of strategic importance in the fuel industry of the North-West of Russia. It is one of the largest in this oil and gas province. An important role is played by proximity to sales markets.
The Usinsk deposit is structured as an anticlinal-type rock fold whose size is 51 km in length and the thickness of the sedimentary cover is about 7-8 km. Oil deposits are located at a depth of 1 to 3.4 km. In terms of water cut, the field is at a late stage of development, and the amount of depleted reserves is only 7.7%. The southern and western parts of the reservoir are practically not covered by production drilling.
Rocks uncovered by the deepest well at the anticline elevation (5000 m) belong to sediments of the Lower Silurian period. The explored deposits are characterized by terrigenous deposits of the Middle Devonian system (the main source of production), the Upper Permian, as well as the Visean, Serpukhov and Famennian layers, which are completely located in the stone-coal-lower Permian complex.
Forecasted Stocks
The balance reserves, the development of which is currently economically feasible, amount to about 960 million tons. The Usinskoye oil field is the largest in the Komi Republic. Oil production on it gives more than a third of the total amount of hydrocarbons explored in this subject of the Russian Federation.
According to preliminary estimates, this volume should be enough until 2030. When conducting additional exploration, an increase in stocks is possible. The operator of this field is Lukoil.
Lithology
The Lower Devonian sediments in the Usinsk deposit are represented by 3 sections (their thickness is indicated in brackets):
- lower (> 1050 m);
- medium (<175 m);
- upper (909-1079 m).
They are composed of the following types of rocks:
- calcareous clay;
- marls;
- carbonate clays;
- dolomites;
- anhydrites with interlayers of clays and marls.
The Visean tier consists of clays; in its upper part, a powerful stratum of carbonate rocks begins, which contains a deposit of highly viscous oil.
Oil properties
Oil Usinskoye field has the following characteristics:
- density - 0.89-0.95 g / cm 3 ;
- sulfur-containing compounds - 0.45-1.89%;
- dynamic viscosity - 3-8 Pa ∙ s (heavy, highly viscous reservoir fluids);
- the maximum content of resinous substances is 28% (northern region of the deposit);
- the content of porphyrins in the form of a vanadium complex is up to 285 nmol / g (increased).
The following compounds predominate in the chemical composition:
- saturated hydrocarbons: alkanes, gonanes and hopanes;
- arenas: naphthalene, o-diphenylenemethane, phenanthrene, tetrafen, fluorantene, pyrene, perylene, chrysene, benzfluorantenes, benzpyrenes.
The concentration of certain types of hydrocarbons varies over the area of the field. So, in its southern part the largest amount of carboxylic acids is detected, and in the northern - the minimum. The oil of this field is generally characterized by a high content of metalloporphyrins and organic acids.
Discovery story
The Usinsky district field was discovered in 1963. In 1968, a powerful fountain was obtained from a depth of about 3100 m (prospecting well No. 7), which produced 665 tons of oil per day. Light oil was produced in the Serpukhov over-horizon in 1972. Initially, this deposit was classified as simple by geological structure.
By 1985, scientists found that the section of the field is more complex, since it has zonal changes in conditions (erosion and interruption of sedimentation), which leads to sharp changes in the thickness of the productive formations and various types of intervals. The tectonic activity of individual zones caused the emergence of vertical fracturing, which also complicates the development of deposits.
In 1998, the geological structure of the field was revised. In some areas, there was a lack of stratification in the form of breakthroughs of bottom water. Also, geologists have established the development of reef-type buildings. The vault part of the Usinsk deposit in the early Permian period towered in the topography of the seabed.
The ideas about the structure of the deposit constantly changed as new information appeared. Seismic surveys in 2012 showed the presence of a large number of tectonic disturbances - cracks. They are most often vertical and are sometimes grouped into 3-4 systems. Cracks in carbonate rocks are not limited to the contact zone of two layers, but pass through several of them at once.
High vertical fracturing and a weak clay cover of the Lower Permian reservoir caused a loss of light hydrocarbon fractions and contributed to the formation of a highly viscous oil field.
Production
Since the reservoir fluid of the Usinsky field has an abnormally high viscosity, its production by traditional methods (rod, centrifugal borehole pumps and other methods) is difficult. By 1990, reservoir pressure had dropped to a critical level. To solve this problem, experts from the Swiss company TBKOM AG were invited. Together with Komineft OJSC, in 1991 the Nobel Oil enterprise was established, the management of which introduced the technology of areal oil displacement by steam at the field. This made it possible to increase the yield of reservoir fluid by 4 times.
Various methods of field development are used and tested on the territory of the deposit - drilling deviated and horizontal wells, a method of thermogravitational drainage of the formation, steam cyclic treatment, combined injection with chemical reagents. However, given the existing thickness of the formation, it cannot be completely covered by heat exposure. Areal injection and steam cyclic treatment covers only about 20% of the oil reserves.
In 2002, Nobel Oil went bankrupt. The company was acquired by Lukoil.
Analysis of the production of this field shows that on average 2 times more oil was produced from watered wells than among those that were stopped due to low reservoir pressure or a drop in productivity. In the latter case, the termination of operation occurs before the completion of the development of the covered reservoirs. This is due to their low permeability, which can be improved with the help of artificial heat.
Heat treatment
The thermogravity method was tested about 30 years ago in Canada. Its principle is to heat the reservoir with hot steam, so that highly viscous oil becomes as mobile as conventional.
In the traditional embodiment, wells for production and injection are drilled at neighboring points. At the Usinskoye field, this technology was changed - the impact was from oncoming wells at opposite points.
The steam injection well in such a scheme is drilled higher than the production one. Steam is continuously pumped into it. A peculiar expanding steam chamber is formed. At its boundary, steam precipitates into condensate and flows under the influence of gravity into the bottomhole zone of the producing well.
Thermoelastic expansion of the reservoir fluid occurs at temperatures in the range of 200-320 ° C. In addition to steam, a large amount of carbon dioxide is generated in the reservoir, which contributes to the displacement of oil. Due to this process, oil recovery is increased by 50%.
Water intake
Due to the presence of a large stock of steam injection units in the reservoir area, there is a great need for fresh water. It is provided by the Yuzhny water intake of the Usinskoye oil field, where liquid is prepared, stored and distributed.
In 2017, the project on the technical re-equipment of water intake began. Technical facilities, water treatment facilities, a pipeline system were updated, a new diesel power station was built. The modernization of this facility will increase technical capabilities and increase oil production at the Usinskoye field.