Would an oil embargo be placed by the US? Wouldn't they choose another type of punishment for the war with China?
I mean, the Japanese war machine will be fueled by themselves, no worries anymore. Hell, they can expand.
IIRC the oil embargo was because the Japanese occupied French Indo China.
My guess is that the Pacific War still happens. Although Japan should be self-sufficient in oil by this point it still needs other raw materials like iron ore and rubber from the East Indies.
OTOH if synthetic rubber can be made from the type of oil the Manchurian fields produce then that's another thing they don't need the East Indies for.
This oil field, even if optimally exploited does not get Japan out of the embargo hole. The Embargo Acts covered a wide swath of economic activity. Perhaps the most important part was freezing all Japanese bank accounts in the US. Japan was not only heavily dependent on US banks for short term and long term loans/investment capitol, but the New York banking center was important for Japans conduct of its global trade. Other than London there were no good alternatives.
Cargo shipping; in 1940 over half Japans port intake and discharge of material was in foreign flagged ships. The embargos stalled the flow of raw materials and finished goods in & out of Japans ports. Conflicts between industry, the army, and navy prevented using the remaining cargo fleet to full efficiency & a crash program to build new ran up directly against the lack of steel and the need for warship construction. Even with adequate steel the merchant fleet would have not reached necessary capacity until maybe 1945. long after Japans economy collapsed.
Raw Materials: Steel. Aluminum. Alloys, Chemicals, Lumber.... were included in the embargos. Japan had built up a 6-12 month reserve, depending on the item. The ability to replenish that was problematic, lacking both transportation, cash or credit to pay with, and any sources to purchase from.
OTOH if synthetic rubber can be made from the type of oil the Manchurian fields produce then that's another thing they don't need the East Indies for.
Rubber was one item Japan had. Occupation of French Indochina gave Japan control of the Michilen rubber plantations. A fair portion for the worlds natural rubber supply.