Petroleum was discovered in the Usinsk area in the mid 1960ies and remains one of the major oil producing regions of Russia ever since. After over 30 years of production, some of the fields reach their maturity and require stimulation to counterbalance the natural production decline. Given the remoteness of area, stimulation methods were considered that don’t put a high burden on the infrastructure in place. Viscos Energy’s binary mixture technology was hence a natural choice, as all chemicals can be transported in solid form and be mixed on site. The stimulations have been performed together with the Institute of Biochemical Physics of the Russian Academy of Sciences.
The six test wells are in a limestone formation at a depth of approximately 1500 meters (4500 ft). They have a highly developed system of fractures and have a water cut of approximately 45%. The porosity is 10%-25%. The viscosity is around 400 centipoise.
A well has been selected as a test well to reconfirm the reservoir characteristics and verify the treatment plan for the stimulation wells. This first well was treated with 6 tons of chemicals (mostly ammonium nitrate and sodium nitrite) as well as catalysts. The treatment time itself was only a few hours, after which the well was shut in and the reaction monitored. Following the small scale verification, another five production wells were stimulated. Each well was stimulated for about six hours.
During the treatment the formation was heated to a temperature of up to 300°C, while the original reservoir pressure was restored. The high temperatures improved the oil’s viscosity around the well head and in the formation. CO2 produced as a result of the chemical reaction helped to sweep the oil out of the formation.
The wells stayed shut in between one and three days before production was restarted. Temperature and pressure in the formation were constantly monitored during the soaking stage. When moving to the production stage, all wells showed an initial production peak that is in line with other thermal stimulations, e.g., cyclic steam injection. This short term peak is primarily a result of the thinning of the oil generated by the increased formation temperature.
One year after the stimulation, the production dropped by around 30% from the values charted above. Each well that was previously effectively shut down produced 15,000 barrels of oil in average during the first year after the treatment.
The long term effect is a major difference to the classical cyclic steam stimulation, which requires much more frequent treatment than the binary mixture technology.
The success of these initial stimulations led Lukoil to use the pilot wells as a template for future treatment in the Usinsk area.
Download: Binary Mixture treatment in Usinsk
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