Developing Geothermal Energy in Croatia by Using Oil Wells for Power Generation

Abstract

Pannonian is a sedimentary basin developed in Central Europe extending to northern Croatia in its southern part. Oil and gas exploration and exploitation activities had been conducted for the last 60-70 years, and thousands of wells have been drilled. Temperature measurements conducted in those wells have revealed anomalous heat fluxes up to 110 mW/m2 in that part of the country. It is believed that thinning earth crust in that region created high heat flow and also helped the formation of hydrocarbon resources within the sedimentary series. Geothermal fluids circulate in the bottom of sedimentary series in highly fractured carbonate rocks which overly metamorphic basement. Sedimentary series have deposited in grabens which, in turn, have created favorable structures for circulation of deeply laying geothermal fluids. These are similar structures to Aegean region of Turkey and Basin and Range of USA. They are deeply seated occurrences with almost no outflowing regions to the surface. Had no hydrocarbon exploration been conducted they would not been unearthed. Power generation project have been developed in Velica-Ciglena license are in which four abandoned oil wells are used, two for production and two for reinjection. It was planned a 15 MWe power generation capacity with 800 t/h flow rate obtained from production wells. This study first introduces regional and the area’s geological setting, including structural geology. Then, it puts forward planning and execution stages of rehabilitation of those oil wells thorough workover operations converting them finally geothermal wells, and afterwards, testing of new geothermal wells for the project target. Finally, it presents the basis of power generation capacity and future vision.