Sarir oil field

The Sarir Field was discovered in southern Cyrenaica during 1961 and is considered to be the largest oil field in Libya, with estimated oil reserves of . Sarir is operated by the Arabian Gulf Oil Company (AGOCO), a subsidiary of the state-owned National Oil Corporation (NOC).

Location

The Sarir field or, more specifically, Sarir C is on west edge of the Calanscio Sand Sea at the southeast margin of the Sirte Basin. Sarir C, which is part of a three-field complex, is 56 km long and 40 km wide covering 378 km². To its north is Sarir L, covering . Situated between the two is a much smaller Sarir North pool. Estimated ultimate oil recovery from Sarir L is .

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 .

Discovery

For years BP avoided using gas detectors on its oil platforms, citing numerous false alarms. However, in 1961, Baroid was hired to set up gas detectors on BP's Libyan wells. C-1-65 gave high readings. This was assumed to be a false alarm, but high readings persisted. Examinations of shale caving samples revealed oil-stained sand grains at the bottom of the plates. 61 m of petroleum play was drilled. The top play in Lower Cretaceous sandstones occurred at 2631 m. On drill-stem tests C-1-65 produced at a rate of .

Post-Discovery

C-1-65 had an oil column exceeding 76 m, above predicted closure for its shallow reflection structure. Although seismic maps gave structural indications, details were unreliable at the reservoirs top 1676 m below. Thus, while the second and third wells were drilled, a seismic refraction survey was shot. It gave control over the basement structure, but since the first four wells proved reservoir sands varied from 141-410m in thickness over a relatively short distance, the survey gave little control over the trapping structure. Seismic maps on both horizons and subsurface information showed the reservoir structure and helped limit drilling in dry holes.

After discovery continuous drilling occurred with up to five rigs at a time. Initially, short outsteps up to 4 km were made, followed by bolder drilling to confirm reserves and justify costs for a 516 km oil pipeline to Tobruk. Once confirmed, C-1-65 was steadily drilled on a 2 km grid spacing. At this time, two smaller fields were discovered: Sarir North and L-65.

In May 1965 five infill wells were sabotaged. The incident occurred during the reign of King Idris before the 1969 coup led by Colonel Qaddafi. The wild wells were not reported in the news media and the perpetrations not revealed. Until the Persian Gulf War of 1991 this was the largest simultaneous well fire ever. In recognition of the number and ferocity of the blowouts BP called for the fire fighter Red Adair