The Permian-Carboniferous reservoir of the Usinsk field is one of the largest objects in the world with unconventional reserves of heavy oil. Despite the long history of the development of the reservoir (over 35 years), the cumulative oil recovery is less than 10.0 %. Difficulties in the development of the reservoir reserves due to non-Newtonian properties of the saturating oil with a viscosity of 700 mPa*s and a unique geological structure of a massive reservoir, which is represented by a 300 m carbonate strata of the Middle and Upper Carboniferous and Lower Permian age located at a depth of – 950 to −1500 m and underlained around the perimeter by the active aquifer. The prospects for increasing the oil production of the reservoir are associated with the introduction in the development with the help of innovative thermal technologies its poorly drilled edge area, in which almost one-third of all reservoir reserves is accomulated.
This article is devoted to a discussion of the results of thermo-hydrodynamic modeling performed on the sector models and aimed at selecting the most effective option of the further development of the edge area of the reservoir, for which it is advisable to consider the use of multiple cyclic treatments of wells with radial horizontal bores by dry superheated steam in combination with the central hot water flooding into injecting wells.
In carbonate reservoirs with heavy oil, the implementation of "classical" thermal EOR methods such as cyclic steam stimulations, steamflooding, and steam assisted gravity drainage usually demonstrates a lower efficiency in comparison with sandstones. The key performance problems are a very complicated porous structure of carbonates represented by matrix blocks, fractures, and vuggs, and a negative wettability of carbonate rocks, which remains mostly oil-wet even with heating. These suggestions are fully confirmed by actual and laboratory results of the Permian - Carboniferous reservoir of the Usinsk field located in Northwest European Russia. The reservoir has the largest heavy oil remaining reserves in the carbonate reservoirs of Russia. Since the viscosity of its oil is more than 700 mPa*s, in some areas of the reservoir, there is a steam injection at ~300°C and ~10 MPa, which are being used for 25 years via vertical and horizontal wells. However, the current oil recovery numbers of the pilots are estimated only between 12 and 15 %. This work includes the analysis the results of recently conducted experimental studies with stacked core models and the actual production and injection data of the thermal pilots with different well configurations.
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