Review of Miscible Flood Performance, Intisar "D" Field, Socialist People's Libyan Arab Jamahiriya
Authors: DesBrisay Charles L. , El Ghussein Bassam F. , Holst Peter H. , Misellati Azzam 
Published: December 2007

Summary
One of the largest miscible gas injection projects in the world is in its 12th year in the Intisar "D" field in the Socialist People's Libyan Arab Jamahiriya. As of March 31, 1981, cumulative oil production totaled 890 MMbbl (141.4 × 10 m) of oil, or 56 recovery of the estimated stock-tank original oil in place (OOIP). This past performance and recent simulation studies indicate a final recovery efficiency on the order of 70 %.

Introduction
The Intisar "D "reservoir is a major oil field in the Sirte basin of the Socialist People's Libyan Arab Jamahiriya. It was discovered in 1967 and is estimated to have had 1,600 MMSTB (254.4 × 10 stock-tank M) OOIP. The field has been developed with bottomwater injection for pressure support and crestal high-pressure miscible gas injection for enhanced oil recovery and gas conservation. It has been the subject of earlier publications on engineering and geology.
This paper presents details of the continuing reservoir performance and the sixth reservoir simulation study. This simulation work was concluded in March 1980 before two significant events further affecting reservoir performance took place. In April 1980, production was reduced from 155,000 STB/D) (24 600 stock-tank m /d) to about 75,000 STB/D (11 900 stock-tank m /d) as part of a national prorationing schedule. At the end of July, control of Well D9 was lost during a workover. At that time the field was completely shut-in for about 3 weeks for safety reasons, and efforts to kill Well D9 were not completed successfully until Jan. 1981.
Twelve and one-half years of reservoir performance history are reviewed. During this time, 890 MMbbl (141.5 × 10 m) of oil, or 56% of the stock-tank OOIP, have been produced. Reservoir withdrawals have been matched by the injection of 670 MMbbl (106.5 × 10-6 m3) of water and 1.420 Tcf (40 × 109 m3) of gas to maintain pressure at or near the 4,000-psi (27 580-kPa) level necessary to ensure miscible displacement.
Field performance results, including the advance of the gas/oil and water/oil contacts (GOC and WOC), have been history matched with a three-dimensional (3D), 1,615-grid, two-component black-oil simulator, and preduction runs have been made to evaluate future performance under various operating alternatives. The simulator prediction runs indicate that the final oil recovery efficiency for this dual displacement process will be approximately 70%. This high recovery is attributed to effective miscible displacement and gravity drainage together with efficient bottomwater displacement.

Discovery and Development
The Intisar "D" oil field was discovered in Oct. 1967 with the completion of Well D1-103, the fourth well drilled by Occidental of Libya in their 465,000-acre (1.9 × 10-9 Mm3) Concession 103. Well D1-103 encountered the oil-bearing Upper Paleocene carbonate reservoir at a depth of 8,946 ft (2727 m) and the WOC at 9,834 ft (2997 m), yielding 888 ft (270 m) of gross productive interval. The field covers an area of 3,325 acres (1.3 × 10-7 m3) and is in the east-central pan of the prolific Sirte basin in the Socialist People's Libyan Arab Jamahiriya, 220 miles (354 km) south of Benghazi and 525 miles (845 km) east-southeast of Tripoli (Fig. 1).
During initial development 36 wells were drilled, of which 13 were originally producers, 16 were water injectors, and 7 were gas injectors. Development drilling was complete by May 1970.
JPT
P. 1651^