Norway's Johan Sverdrup oilfield, the North Sea's largest with an output capacity of up to 470,000 barrels of oil per day, will have to close down production unless a strike among workers ends by Oct. 14, operator Equinor said on Wednesday.Four smaller oil and gas fields will likely also shut as a result of the strike as early as Oct. 10, on top of six fields that closed earlier this week, an Equinor spokesman told Reuters…