INA Oil Company, Plc. Zagreb is a Croatian company engaged in the exploration and production of oil and gas, refining and distribution of petroleum products. An enormous quantity of hazardous waste is generated in oil and gas production and thus has to be disposed in a permanent and safe manner. In recent years, INA has been disposing waste by injection into exploration dry wells and production depleted wells. A specific waste disposal problem has arisen in the process of gas and condensates in Molve, Kalinovac, Stari Gradec and Gola fields. Namely, mercury-sulfide, sulfur slurry and heavy metals have been separated during the production of gas and condensate. Mercury-sulfide has been separated in the process of active coal utilization. The disposal of active coal saturated with mercury-sulfide is a very complex issue. So far, the methods of mercury-sulfide disposal have not been ecologically acceptable. However, on the basis of new experience and knowledge in that field, waste dispersed in a bentonite suspension may be disposed in a permanent and safe manner into appropriate geological formations. In the same way, when combusting various types of industrial and municipal waste, the problem of residual ash disposal emerges. Such residual ash contains heavy metals which may be permanently disposed by using the above mentioned method. This paper deals with the experience of waste disposal by deep well injection in the Republic of Croatia.
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