About 130 cubic meters of oil spilled over an area of about 1,000 square meters at the Trebs field in the Yamal-Nenets autonomous district, the local branch of the Emergency Situations Ministry reported on its website, as cited by Interfax.
The field is being developed by oil company.
No fire broke out following the spill, and no one was injured. Cleanup work is now under way.
This was the second accident at the Trebs field during well re-entry by oil-field services company Burs.
In April, an unsealed well head spewed a mixture of oil and gas into the surrounding area. The Federal Service for Environmental, Technological and Atomic Inspection said the accident occurred in part because of Burs personnel's lack of experience.
In the wake of the spill, Bashneft fired Alexander Dashevsky, senior vice president for oil and gas production, and Rinat Nagayev, head of the oil and gas department.
Bashneft said it is already implementing a program aimed at preventing similar accidents in the future.