Pre-Discovery
In 1957, the Libyan government granted Concession 65 to Bunker Hunt, an independent oil producer from Texas. By 1960, BP had assumed a 50% interest in C-65 and became the operator. After large discoveries in the Sirte Basin in 1958 and 1959, a reflection seismology survey was conducted on C-65, followed by an aeromagnetic survey showing the existence of large structures. Later that year, BP began drilling in C-65, 80, and 81, targeting Paleocene and Cretaceous carbonates that had yielded discoveries in the Nasser (Zelten), Defa, Raguba field, and Bahi fields. Mobil discovered Cretaceous basal sand at Amal in 1959, but early results did not recognize its full potential.
Before drilling the C-1-65 well, BP drilled six tests to basement in C-65, 80, and 81. None had high hydrocarbon shows. Eocene, Paleocene, and Cretaceous carbonates were generally freshwater bearing, and basement highs were draped in Late Cretaceous shales. There were occasional redbed vestiges at the shale-basement contact and bitumen veining. Many wells proved expensive due to lost circulation in Paleocene-Cretaceous carbonates and caving in underlying Late Cretaceous shales. This was so severe that the Sarir field was nearly bypassed because oil was not anticipated in the Nubian Formation. However BP's chief geologist insisted a basement core be taken in every well. This turned out to be a good decision, since C-1-65 was subsequently shown to be a prolific reservoir with initial production rates of 20,000 bbl/d (3,200 m3/d).
Read more about this topic: Sarir Field