Usinskoye field has been in operation since 1977. Its development is carried out in very difficult geological conditions associated with the characteristics of the deposit. Reservoir fluid refers to hard-to-recover fluids, as it has an abnormally high viscosity. However, in recent decades, high-viscosity oils have been considered as the main reserve of world production. Their reserves in Russia, according to various estimates, 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 reservoirs has become particularly relevant.
Where is the Usinskoye field?
Usinsk oil deposit is located in the north-east of the region of the same name in the Komi Republic. Its area covers the Pechora Lowland and the basin of the Kolva River (the right tributary of the Usa River). The nearest city is Usinsk. The location of the Usinsk oil field "Lukoil" is associated with a transitional natural zone from the tundra to the taiga. The climate here is sharply continental, the average annual temperature is -25 °C. In winter, the thermometerdrops to -55 °С. The relief of this area is a low, heavily swampy 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.
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. Proximity to sales markets also plays an important role.
Usinskoye field is a fold of rocks of anticline type, the size of which 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 deposit are practically not covered by production drilling.
Rocks recovered by the deepest borehole on the rise of the anticline (5000 m) belong to the deposits of the Lower Silurian period. Explored deposits are characterized by terrigenous deposits of the Middle Devonian system (mainsource of prey), the Upper Permian, as well as the Visean, Serpukhovian and Famennian stages, which are completely located in the Carboniferous-Lower Permian complex.
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 provides more than a third of the total amount of hydrocarbons explored in this subject of the Russian Federation.
This volume, according to preliminary calculations, should be enough until 2030. During additional exploration, an increase in reserves is possible. The operator of this field is Lukoil.
Lower Devonian deposits in the Usinsk field 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:
- carbonate clays;
- anhydrites with interlayers of clays and marls.
The Visean stage consists of clays, in its upper part a thick sequence of carbonate rocks begins, which contains a deposit of high-viscosity oil.
Properties of oil
Oil from the Usinsk field has the following characteristics:
- density - 0.89-0.95g/cm3;
- sulfur-containing compounds – 0.45-1.89%;
- dynamic viscosity - 3-8 Pa∙s (heavy, high-viscosity formation fluids);
- maximum content of resinous substances - 28% (northern area of the deposit);
- content of porphyrins in the form of a vanadium complex - up to 285 nmol / g (increased).
The chemical composition is dominated by the following compounds:
- saturated hydrocarbons: alkanes, gonanes and hopanes;
- arenes: naphthalene, o-diphenylenemethane, phenanthrene, tetraphene, fluoranthene, pyrene, perylene, chrysene, benzfluoranthenes, benzpyrenes.
The concentration of certain types of hydrocarbons varies across the field area. So, in its southern part, the largest amount of carboxylic acids is revealed, and in the northern part, the minimum. Oil from this field is generally characterized by a high content of metal porphyrins and organic acids.
The field in the Usinsk region was discovered in 1963. In 1968, a powerful fountain was obtained from a depth of about 3100 m (exploratory well No. 7), which produced 665 tons of oil per day. Light oil was produced in the Serpukhov superhorizon in 1972. According to the geological structure, this deposit was originally classified as simple.
By 1985, scientists found that the section of the field is more complex, as it has zonal changes in conditions (erosion and breaks in sedimentation), which causes sharp changes in the thickness of productive layers and various types of intervals. The tectonic activity of individual zones caused the emergence of a verticalfracturing, which also complicates the development of the deposit.
In 1998, the geological structure of the deposit was revised. In some areas, the absence of layering in the form of outbursts of plantar waters was found. Also, geologists have established the development of reef-type buildings. The arched part of the Usinskoye field in the early Permian period rose in the topography of the seabed.
Representations about the structure of the deposit were constantly changing as new information appeared. Seismic exploration in 2012 showed the presence of a large number of tectonic faults - cracks. They are most often vertical and 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 weak shale seal of the Lower Permian deposit caused the loss of light hydrocarbon fraction and contributed to the formation of a high-viscosity oil field.
Since the reservoir fluid of the Usinskoye field has an abnormally high viscosity, its production by traditional methods (rod, centrifugal well pumps and other methods) is difficult. By 1990, reservoir pressure dropped to a critical level. To solve this problem, specialists from the Swiss company TBKOM AG were invited. In 1991, together with OAO Komineft, 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 reservoir fluid recovery by 4times.
Different methods of field development are used and tested on the territory of the deposit - drilling of inclined and horizontal wells, the method of thermogravitational drainage of the reservoir, steam cycling treatment, combined injection with chemical reagents. However, with the existing thickness of the formation, it cannot be completely covered by thermal exposure. Only about 20% of the volume of oil reserves is covered by areal injection and steam cycling.
In 2002, Nobel Oil went bankrupt. The company was bought out by OAO Lukoil.
An analysis of the production of this field shows that, on average, 2 times more oil was produced from flooded 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 covered reservoirs. This is due to their low permeability, which can be improved by artificial heat treatment.
Thermogravitational method was tested about 30 years ago in Canada. Its principle is to heat the reservoir with hot steam, so that high-viscosity oil becomes as mobile as regular oil.
In the traditional variant, wells for production and injection are drilled at neighboring points. At the Usinskoye field, this technology was changed - the impact was made from opposite wells at opposite points.
Steam injection well in such a schemedrilled higher than production. Steam is continuously pumped into it. A kind of expanding steam chamber is formed. At its boundary, steam falls into condensate and, under the influence of gravity, flows into the bottomhole zone of the production well.
Thermoelastic expansion of 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 of wells is increased by 50%.
Due to the presence of a large stock of steam injection plants in the area of the deposit, there is a great need for fresh water. It is provided by the Yuzhny water intake of the Usinsk oil field, where the preparation, storage and distribution of liquid is carried out.
In 2017, the implementation of the project for the technical re-equipment of the water intake began. The technical facilities, water treatment facilities, pipeline system were updated, a new diesel power plant was built. The modernization of this facility will increase technical capabilities and increase oil production at the Usinskoye field.