What is the term used to refer to oil fields that are difficult for people to explore and exploit them?

Question

Do we just refer to it by a simple English term "difficult oil fields" or there is another term that I am not aware?


The political climate of Indonesia has become more stable and has again encourage investment in exploration activities and efforts to increase production. So much that it is expected that in the next few years Indonesia will see an increase again in oil production. It is hoped that several new conducive policies such as the provision of exploration incentives for the DIFFICULT OIL FIELDS and state-of-the-art technology application will contribute significantly to the production increase.

Answer 1

IRANIAN

Answer 2

deep water fields?