The correct answer to this open question is the following.
If Japan were seizing oil fields, they might have invaded the islands in Southeast Asia.
Japan would have invaded places rich in hydrocarbon resources such as Malaysia, Indonesia, Brunel, and Vietnam, that have plenty of oil and natural gas reserves. The Southeast Asia region has been coveted for its many raw materials and natural resources since colonial times. That is why countries such as Great Britain and France used to have colonies in this part of the planet.
Japan might get interested in Jurong Island in Singapore, Diaoyu Island of China, the disputed Spratly Islands. These islands in Asia are rich oil reserves. I think these are the possible answers to the question you have given. I hoped this helped you
