Produced water is always an unwanted by-product for any hydrocarbon producing process. Underground disposal of the produced formation water has many benefits such as minimum or no damage to the environment. However, formation damage arising from injection of water containing impurities is usually of great concerns and poses challenges for maintaining good injectivity of disposal wells. Well stimulation is probably one of the most effective treatment to restore the injection of impaired wells. Therefore, well treatment and optimization always play an important role in cost saving and injectivity improvement.
Although many treatments such as acidizing and mutual solvent have been developed as a standard practice and are widely employed in the oil and gas industry, there is no universal treatment recipe which may be used to effectively stimulate a well without doing any well specific studies. To effectively tackle the injection rate decline issue in water disposal wells, understanding the process, quality of injection water and the nature of the in-situ properties of the formation is vitally important. Therefore, analysis of the formation minerals and lithology, produced water, well performance and field stimulation histories had been thoroughly reviewed and examined to understand the root causes and the mechanisms underlying the rate reduction and how to improve the injectivity. Laboratory experiments had then been organized and conducted for evaluating and optimizing the treatment. Fit-for-purpose well treatments were finally designed and executed for field evaluation. Once the field treatment was done, a thorough review and benchmarking of the treatment job had been performed to capture the lessons learned. More laboratory evaluation may be necessarily carried out for further improvement in the next well treatment.
Applying the above process to the treatment of water disposal wells, a new well specific matrix stimulation treatment had been developed and applied to a few water disposal wells over the last few years. When compared with the outcomes of other types of treatment in history, the injection gain from this type of treatment was significant with a maximum 400% injection increase. Moreover, the improved injectivity had longer effective duration up to 26 months so far. Still a few wells have no signs of injection rate drop. The benefits are obviously enormous in terms of cost saving and injection gain.
Effectiveness of a well specific treatment is rooted into the thorough understanding of the physical and chemical interaction between alien fluids and the in-situ formation. Laboratory evaluation is an important key to the development of a successful treatment recipe, which was showcased by the work presented in this paper. This would enrich the expertise of petroleum professionals in the limited stimulation practice of the water disposal wells.