Artificial Lift Method Selection for Mature Oil Fields: A Case Study

Abstract

As oil production continues, reservoir pressure decreases and oil production rate may not be as high as the plateau production rate. Once any sign of reduction in oil production rate has been observed, improved oil recovery (IOR) techniques are considered to aid the production. However, IOR methods could be accomplished from the beginning of oil production. Among different IOR methods, implementing artificial lift systems is one of the main options especially in brown fields. Artificial lift methods are categorized into pump-lift methods and gas-lift methods. In this study, screening process has been performed to find feasible artificial lift methods. During the screening process, different aspects of reservoir, well and fluid behavior have been studied to find the feasible options and it has been concluded that only ESP and gas lift could be implemented in this particular field. Both of these methods have been studied by simulating an integrated model including the reservoir and all of the candidate wells. So, impact of any variation in reservoir or well properties has been captured during the next 10 years. Three scenarios have been defined to predict the field performance by natural depletion, installing electrical submersible pumps and implementing gas lift system. Although an option might be selected as the best method for the present time, a long term evaluation is able to change the selected method. Integrated modeling the whole system of reservoir and wells provides a better understanding of the impact of different factors on performance of each scenario in long time. By performing a number of sensitivity analysis tests, it has been observed that increasing the water-cut may affect noticeably the performance of lifting systems. So, the pressure and water-cut of the reservoir and wells have been predicted during the next decade. It has been shown that using gas-lift method in the mentioned field has the highest oil recovery factor and the cumulative oil production during the next 10 years is more than 134 MMSTB. The ESP pumping system could lift almost 112 MMSTB oil during 10 years, while the natural depletion system has the lowest recovery and only 13 MMSTB oil could be produced during the same period.