Supplemental Recovery Development of The Intisar "A" and "D" Reef Fields, Libyan Arab Republic

Abstract

Large-scale pressure maintenance programs were begun very early in the producing life of these giant fields to maximize oil recovery and conserve producing life of these giant fields to maximize oil recovery and conserve associated gas. It is estimated that a continuation of these programs will effect a combined recovery of more than 60 percent of the oil originally in place and will conserve nearly 2 trillion cubic feet of natural gas for future use. Introduction Supplemental recovery operations were begun early in the Intisar "A" and "D" Reef reservoirs to maximize ultimate oil recovery, maintain flowing production. and conserve natural gas and gas liquids. production. and conserve natural gas and gas liquids. These giant fields originally contained approximately 4 billion bbl of stock-tank oil. Because the oil in both reservoirs was highly undersaturated, primary recovery efficiency was indicated to be relatively low, necessitating the installation of large water- and gas-injection pressure maintenance programs very early in their productive lives. This paper reviews the reservoir engineering planning and development work that led to the planning and development work that led to the installation of a 500,000 B/D bottom-water injection program in the Intisar "A" field and a combination program in the Intisar "A" field and a combination miscible gas-water displacement program in the Intisar "D" field. The projected peak injection rates in the latter were 700,000 Mcf of gas per day and 400,000 BWPD. A large gas liquids extraction plant, completed early in 1972, also was constructed as an integral part of this gas reinjection project. Water injection was begun in the Intisar "A" field less than 6 months after the held was placed on production. In the Intisar "D" reservoir, water production. In the Intisar "D" reservoir, water injection was started almost coincidentally with production, and crestal gas injection operations were production, and crestal gas injection operations were begun less than 15 months later. These pressure maintenance programs were completely implemented in July, 1971 when the last of three huge gas compressors was commissioned. Thus, the primary and supplemental development of these two fields was completed barely 4 years after the discovery of the first reservoir in April, 1967. This supplemental development was accomplished quickly in order to optimize ultimate oil recovery. It is estimated that these timely pressure maintenance programs will ultimately result in the recovery of approximately three times as much oil from the two fields as would have been realized by primary means alone. In addition, almost 2 Tcf of associated natural gas will be conserved for future use. Discovery and Development The Intisar "A", "C", and "D" field complex is located in the cast-central part of the Libyan Arab Republic's petroleum-rich Sirte Basin. The Intisar "A" and "D" fields are only 15 miles apart and lie within Occidental of Libya's 465,000-acre Concession 103, located about 220 miles due south of Benghazi and 525 miles cast-southeast of Tripoli (see Fig. 1). This concession was awarded in March, 1966, and seismic operations were begun there early in 1967. In April, 1967, the first well drilled on the concession, A1-103, discovered a major oil accumulation when it penetrated oil-bearing Paleocene carbonate rock at a well depth of 9,417 ft. JPT P. 785