Kirkuk is a supergiant oil reservoir located in Iraq. Kirkuk began production in 1934, and 2 billion bbl of oil were produced before water injection was implemented in 1961. From 1961 to 1971, 3.2 billion bbl of oil were produced under pressure maintenance by waterdrive using river water. The 1971 production rate was approximately 1.1 million barrels of oil per day (BOPD). Since then, the field has continued to produce large volumes of oil by voidage-replacement water injection; however, few production details for recent years appear in the technical literature.
The primary pay interval for the Kirkuk field is the 1,200-ft-thick Main Limestone. This interval consists of a series of extensively fractured limestones, some porcelaneous and some dolomitized. These limestones were deposited in a variety of environments—back-reef/lagoonal, fore-reef, and basinal—and have a wide range of porosity and permeability properties. The oil is contained both in an extensive, extremely permeable but low-capacity fracture system and in a low-permeability but high-capacity, matrix-pore system. Also, the reservoir is underlain by a fieldwide aquifer. The oil gravity is approximately 36°API and was approximately 500 psi undersaturated at the original reservoir pressure of 1,100 psia.
The interesting technical aspects of this type of reservoir are the determination of the ultimate oil recovery from the matrix and the time scale of matrix oil recovery. Laboratory experiments can be run using matrix rock samples to determine the water/oil imbibition behavior; however, what matters is the actual reservoir’s matrix/fracture interaction because the fracture density varies considerably. The early water injection showed that within the fracture network there was rapid communication over a distance of more than 20 miles. Water injection initially was peripheral; however, because of low injectivity caused by lack of downdip fracturing, injection was shifted to seven injection wells in the saddle area between the two principal domes of this oil field, one of which had an injection capacity of more than 400,000 barrels of water per day (BWPD).
A 90-day temporary production stoppage in 1967 allowed unique field data to be acquired regarding the matrix/fracture interaction because of the observed changes in the oil/water contact (OWC). It was observed that the OWCs fell in the areas where they were the highest and rose in the areas where they were the lowest. These OWC changes were the result of the countercurrent imbibition process between the fracture network and matrix pore system. From these data, the time-delay function could be calculated on the basis of observed field data. Depending on the assumptions, the half-life was estimated to be 3 to 5 years and the ultimate recovery was estimated at 30 to 45% of the original oil in place (OOIP).
- Al-Naqib, F.M., Al-Debouni, R.M., Al-Irhayim, T.A. et al. 1971. Water Drive Performance of the Fractured Kirkuk Field of Northern Iraq. Presented at the Fall Meeting of the Society of Petroleum Engineers of AIME, New Orleans, Louisiana, 3-6 October 1971. SPE-3437-MS. http://dx.doi.org/10.2118/3437-MS
Noteworthy papers in OnePetro
Grabowski, G.J., Jr. and Liu, C. 2009. Ages and Correlation of Cenozoic Strata of Iraq. Presented at the International Petroleum Technology Conference, 7-9 December 2009, Doha, Qatar. IPTC-13589-MS. http://dx.doi.org/10.2523/13589-MS
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