The Niger Delta Nembe Creek Oil field was discovered in 1973 and produces from middle Miocene deltaic sandstone-shale in an anticline structural trap at a depth of 2–4 km. In June 2013, the company announced a strategic review of its operations in Nigeria, hinting that assets could be divested. While many international oil companies have operated there for decades, by 2014 most were making moves to divest their interests, citing a range of issues including oil theft. In August 2014, Shell Oil Company said it was finalising its interests in four Nigerian oil fields.

Answer this question, if possible (if impossible, reply "unanswerable"): What is the depth of the Niger Delta Nembe Creek Oil field?
2–4 km