The carbon dioxide output from the white storage tank is pressurized by the skid-mounted equipment and injected into a reservoir three to four thousand meters deep through a gas injection well. On the afternoon of November 17th, China Petroleum (7.110, -0.01, -0.14%) Xinjiang Oilfield Branch is implementing gas injection operations in the Mahu well 1 area of the Mahu oil field, using carbon dioxide to drive crude oil extraction.
There are 6 gas injection wells and 12 oil production wells here, forming a five point injection production well network. The injection production wells are 280 meters apart, and the carbon dioxide injected into the reservoir dissolves with the crude oil, forming a mixed phase drive, causing the crude oil to expand, reducing the viscosity and interfacial tension of the crude oil, and promoting more crude oil to flow to the production wells, thereby improving the plateau oil recovery rate.
"Previously, carbon dioxide driven crude oil extraction experiments were conducted in old areas with decreasing crude oil production. This year, for the first time, experiments were directly conducted on production wells," said Qin Ming, an engineer at the Mahu Exploration and Development Project Department.
The area where gas injection operations are carried out is a highly sensitive oil reservoir. Previously, the "horizontal well+volume fracturing" method was used for production, but due to the influence of water sensitivity, the oil recovery effect was not ideal. This year, the Mahu well 1 area was selected for pilot testing. At the same time, gas flooding tests were also carried out for high saturation oil reservoirs in the Ke well 83 area and top gravity gas flooding tests in the Xia well 77 area. Currently, gas injection is fully underway.
Mahu well 1 area is the world's largest sensitive tight conglomerate oil reservoir with low porosity, and crude oil is stored in rock pores that are invisible to the naked eye. "A reservoir with such characteristics, after water injection, actually blocks the pores and crude oil production channels, hence it is called a strong water sensitive area," explained Qin Ming.
Carbon dioxide dissolves with crude oil to form a mixed phase drive, overcoming the influence of water sensitivity. Therefore, the Mahu Exploration and Development Project Department has decided to carry out a new well CO2 injection driven crude oil extraction experiment. According to the design plan, after injecting carbon dioxide into the new well for three months, it is expected to be put into operation in February next year, and the oil recovery rate is expected to increase by more than 20%.
While conducting carbon dioxide driven crude oil extraction experiments on the new well, Mahu Oilfield also injected carbon dioxide into the pre-fracturing stage for the first time this year. "There are more than 10 wells in the south of Zone 5 of Well Ma 2, which have injected carbon dioxide during the pre-fracturing process, with a daily injection of four to five hundred tons of carbon dioxide," said Yang Gang, an engineer from the Mahu Exploration and Development Project Department.
The carbon dioxide driven crude oil extraction experiment in the old area has been further upgraded. The reporter learned from PetroChina Xinjiang Oilfield Branch that in order to achieve a 100% carbon sequestration effect, a test station has been built this year in the well 530 area of the eighth zone of Xinjiang Oilfield Oil Production Plant after years of exploration. "After the trial station is put into operation, carbon dioxide can be recycled," said Wang Bin, the director of the natural gas treatment station at the Second Oil Production Plant.
About 70% of the carbon dioxide injected into the reservoir can be permanently buried underground, and another 30% is accompanied by crude oil flowing out of the wellhead. To prevent carbon dioxide from overflowing from the wellhead, a recovery plant is installed at the experimental station to purify the recovered carbon dioxide and inject it back into the reservoir.
Since 2015, Xinjiang Oilfield has carried out a pilot test of carbon dioxide driven crude oil extraction. As of 2022, a total of 1300 wells have been injected with carbon dioxide gas, injecting over 400000 tons of carbon dioxide and increasing oil production by over 130000 tons.
With the further advance of the pilot test, the demand for carbon dioxide in Xinjiang Oilfield is also increasing. The captured carbon source has also expanded from the refinery in Karamay to several chemical enterprises around the the Junggar Basin, making more space for carbon emission reduction in Xinjiang.
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