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Journal of Petroleum Science and Engineering 42 (2004) 245 – 255 www.elsevier.com/locate/petrol

Intermittent gas lift in Aghajari oil field, a mathematical study
Shahaboddin Ayatollahi a,*, Mostafa Narimani a, Mahmood Moshfeghian a,b,1
a

School of Chemical and Petroleum Engineering, Shiraz University, P.O. Box, 71345-1719, Shiraz, Iran b Department of Chemical Engineering, University ofQatar, P.O. Box 2713, Doha, Qatar

Abstract The gas lift is a widely used method of artificial lift, for which there are different options. Previous work in this regard to optimize the continuous gas lift (CGL) of Aghajari oil field located in the south of Iran was promising. A new intermittent gas lift (IGL) simulator is developed considering all aspects of this artificial lift method includingthe temperature differences between the injected and produced fluids. In order to check the validity of the mathematical model, the intermittent gas lift experimental data, i.e. pressure gradient as a function of time, of Brown [Gas Lift Theory and Practice, Prentice-Hall, Englewood Cliffs, NJ (1967)] were compared with the results obtained by this simulator. The calculated pressure gradientmatched well with the experimental data. For the same system, the pressure under the liquid slug as a function of opening pressure of gas lift valve was also calculated and compared with the experimental data. It was found that ignoring the heat transfer between the injected gas and the liquid slug shifts away the calculated results from the experimental points and therefore, decreasing the accuracy ofthe model. The model then was used to study the Aghajari oil field. The results showed that the production of this oil field will increase significantly using intermittent gas lift method. D 2003 Elsevier B.V. All rights reserved.
Keywords: Gas lift; Artificial lift; Intermittent; Computer simulation; Heat transfer; Two phase flow

1. Introduction Artificial lift is used in petroleumproduction when the energy of the reservoir is not enough to sustain the flow of oil in the well up to the surface with satisfactory economic return. High pressure gas is injected into the well to lighten the column of fluid and allow the reservoir pressure to force the fluid to the surface. The gas that is injected is produced with the reservoir fluid into the low pressure system.

* Correspondingauthor. Fax: +98-711-628-7294. E-mail addresses: shahab@shirazu.ac.ir (S. Ayatollahi), moshfeg@qu.edu.qa (M. Moshfeghian). 1 On sabbatical leave from Shiraz University. 0920-4105/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.petrol.2003.12.015

Oil production operations in Aghajari oil field in south of Iran are mature. Initially discovered in the 1938, cumulativerecovery from this giant oil field with more than 15 billion barrels of recoverable oil has reached 10 billion barrels so far. Iran’s Aghajari Field, which experienced peak production of 1 million barrels a day in 1974, and then produced a steady 850,000 barrels per day for 17 consecutive years, is now going to consume 3 billion cubic feet of South Pars gas to prop up production of only 187,000 barrelsper day. This field operates 165 wells, 60 of them under artificial gas lift process. Typical wellbores include 3 1/2 and 4 1/2 in. tubing set in 9 5/8 in. production casing. Due to the importance and demand of gas lift process, developing a mathematical model to simulate this process is

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of highinterest. The model may be used to find the optimum operational condition.

2. Intermittent gas lift Selection of the proper artificial lift method is critical to the long-term profitability of the oil well; a poor choice will lead to low production and high operating costs. The gas lift is a widely used method of artificial lift, where gas is injected in the production well providing energy to...