The model experiments regarding the conversion of organic matters from carbonate rock samples of Dankov-Lebedyan deposits of Zelenogorskaya area and siliceous-carbonate rocks of Semiluki-Mendym deposits of Berezovskaya area of Domanic formations of Romashkino oil field were carried out. Two types of experiments were carried out: (1) the hydrothermal treatment of rocks at a temperature of 350°C in the presence of carbonic acid and a water content of 30%; (2) pyrolysis at temperatures of 350 and 600°C in the presence of hydrogen. The yield and quality of extracted hydrocarbons from the rocks depending on the mineral composition of rocks, content and composition of organic matter, and thermal stability of kerogen under hydrothermal influences were evaluated. Application of electron paramagnetic resonance in pyrolysis processes revealed the difference in mineral content of rocks (Mn2+, SO3−, and SO2− ions) and free radicals R∗, as well as in vanadyl ion (VO2+) concentration. It is established that an increasing temperature of pyrolysis promotes the formation of new free organic radicals in rock samples: in Domanic rocks of Semiluki-Mendym deposits at 350°С and in carbonate rocks of Dankov-Lebedyan horizon at 600°С. This indicates different ability of oil-generating potential of rocks with hydrothermal and pyrolysis technologies.
Low-salinity waterflooding (LSW) and its effect on oil recovery factor have been studied around the world during the last 30 years. Low-salinity/fresh water was used in the initial stage of waterflooding because of deficiency of produced water. The Pervomaiskoye oil field in Republic of Tatarstan is one of the examples. Waterflooding started in 1966. Water was taken from the nearest water source, the Kama River. After more than 40 years, about two PVI has been injected, and 30.1% of this injected water was low-salinity. This paper presents the results of laboratory study of double core flooding using high-salinity (formation) and low-salinity (river) water. Two plugs were taken with the clay content of about 0.8% and 0.1% and the permeabilities of 432 and 291 mD, respectively. Dead oil was used with the viscosity of 37.5 mPa.s. TDS values were about 252,738 ppm for high-salinity water and 848 ppm for low-salinity water. Dry and vacuumed plugs were saturated, first, with high-salinity water, then, with oil, to simulate connate water saturation; then, oil was displaced with the same water. After this, the cores wre restored to the connate water by a secondary oil flood, and finally, LSW was simulated. In both cases, oil recovery was recorded and fines release was analyzed. Processing of the low-salinity corefloods data by a numerical model shows a two-fold decrease of water relative permeability for the first plug and 1.5 times reduce of residual oil saturation for the second plug. Fines release and formation damage was observed in the first plug and wettability alteration in the second plug. Oil relative permeability didn't change. Also, the unusual behavior of water relative permeability in response to low-salinity waterflood was observed, namely, it decreased at water saturation values more than 0.4. To investigate the low-salinity EOR effect seven pilots on the Pervomaiskoye field were analyzed, with high-salinity waterflooding following LSW. Incremental oil recovery for these pilots, that has been achieved by now, is approximately 5-9%. Calculations of low-salinity EOR effect in the field show that LSW through 96 injectors ensures to date the incremental recovery factor of 3-4%. The reservoir 3D model of five-spot pattern for the Pervomaiskoye field for fines-assisted waterflooding gave incremental oil recovery by 5-11%. The laboratory relative permeabilities were used in the model. Incremental oil recovery depends on the number of the flooded layers.
Low salinity waterflooding is presently one of the most promising enhanced oil recovery (EOR) methods. Wettability alteration and residual oil decrease are the most important EOR mechanisms of low salinity waterflooding. However, the mobility control EOR due to fines migration, induced by low salinity water, and the consequent flux diversion is also an important feature of the smart waterflooding. We analyze the limited available field data from 10 years of low salinity water injection in Bastrykskoye field. The mathematical model for fines-assisted waterflooding is used for history matching resulting in good agreement between the field and modeling data. The model is used to compare recovery factor for two scenarios of low salinity water injection and formation (normal) water injection. Low incremental recovery and low decrease in the amount of produced water during the development of Bastrykskoye field is explained by the production of significant amount of the reservoir water before the commencement of low salinity water injection.
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