Abstract
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.
