Application of Produced Water Re-Injection Design and Optimisation in Carbonate Oilfield Containing Hydrogen Sulfide
Authors: Hu Dandan , Li Qianyao , Shen Jiangfeng , He Being , Wu Yuanbing , Li Wenhuan , Wang Ze 
Published: October 2024

The production of oil and natural gas has a great impact on modern industry, but a large amount of produced water is generated during the oilfield development process, especially for large-scale oilfield. The water production in the produced liquid gradually increases, and direct discharge of produced water can have adverse effects on the environment, which has become a serious concern. With the long-term stable production of oilfields achieved by these operators in the Middle East through water injection development, the shortage of injection water sources and the urgent need for water injection to maintain pressure in oil reservoirs, the high investment treatment costs for produced water with high hydrogen sulfide content, and the compatibility between produced water re-injection and reservoir compatibility have become prominent issues. It is urgent to maximize the economic benefits of oil fields and meet the environmental protection requirements of countries.

The paper focuses on the challenges and bottlenecks encountered in the re-injection of produced water in the D oilfield with high hydrogen sulfide content in the Middle East. Based on indoor core experiments, production performance analysis, wellbore corrosion monitoring, and differentiated injection allocation, an optimization strategy and design plan for re-injection of produced water are proposed. In the paper, the parameters and characteristics of different water qualities were determined through indoor experiments for the available water resources in the oilfield. It was clarified that the produced water is high in salinity, chloride ion content, sulfide content, and oil content, while the fresh water is oxygen and bacteria containing. The mechanism and reasons for the decrease in injectivity and corrosion of wellbore and surface pipelines caused by early implementation of produced water re-injection were analyzed. The paper proposes an optimization method for fresh and produced water injection based on reservoir physical properties, H2S content, reservoir type, and production performance. An integrated fresh and produced water injection plan is designed. High hydrogen sulfide and low permeability reservoirs are connected to fresh water pipelines, and low H2S and medium high permeability reservoirs are treated with produced water and re-injected, combined with new anti-corrosion pipes to suppress corrosion in the surface injection system.

The optimization strategy and technical Roadmap in the paper has been applied in D oilfield, which can avoid pipeline corrosion and formation pollution, reduce the complexity of injected water quality, meet the water quality requirements of poor physical properties layers, and play the role of low salinity water in improving oil recovery in low permeability reservoirs. It is beneficial for corrosion prevention and scale inhibition, full utilization of produced water, and maintaining the injection capacity of water injection wells, achieving the goals of good water injection development effect and low investment cost.

Most carbonate reservoirs in the Middle East contain hydrogen sulfide and lack fresh water sources. D oilfield improved the development effect of low permeability reservoirs, reduces corrosion and the cost of OPEX through optimisation and application of produced water re-injection. This study has good reference significance for similar oilfield produced water re-injection programs.