There has been a long tradition of process waste disposal into existing deep wells in Croatia. Previously, liquids were separated from solids and injected into geologically appropriate formations. Solids were left in the existing mud pits or transferred into selected deposits. An essential disadvantage of such a procedure was the settlement of heavy metals and their penetration into sediments containing fresh water. The authors of this project have elaborated a new technology that presumes joint injection of liquids and solids into deep wells properly designed, so that the slurry may penetrate through geologically adequate formations. Wells have been classified into three groups upon which the following requirements are imposed: (1) reservoir pressure of a selected geological formation is lower than the hydrostatic one; (2) reservoir pressure is higher than the hydrostatic one, but lower than the fracturing pressure of that formation; and (3) possibility of obtaining an injection pressure that creates fractures and thus enables waste disposal. With regard to the fact that a relatively large number of dry exploration wells and depleted production wells exist in Croatia, the study illustrates that a number of wells can be classified into these three groups.
Currently, the technological waste created during drilling, workover, oil and gas production and refining processes is permanently disposed by applying a specific procedure developed in Croatia. Besides, there has been a serious debate over the possibility of a permanent low and middle radioactivity waste disposal created in health services, pharmacy and food industry, following the referred procedure. For that purpose, an adequate law regulation to enable the application of the referred procedure is under preparation.