Geothermal reservoir stimulation is a standard technique for enhancing naturally low permeable reservoirs or to overcome formation damage. Hydraulic, chemical or thermal stimulation are applied as standard procedures. Those are supposed to solve individual problems, which might lead to only short-term reservoir enhancement. Constraints in geothermal systems are often more complex and change with time. Therefore, we developed a Feedback Adjustment Procedure for sustainable soft stimulation concepts. The procedure starts with a multidisciplinary database and pre-evaluates potential scenarios. The most important step in the procedure is a re-evaluation loop after each treatment that ensures regularly updated knowledge on site-specific processes. The loop ensures an adapted stimulation concept ending in sustainable reservoir enhancement. At our geothermal test site in Klaipeda (Lithuania) four wells target a highly permeable Lower Devonian sandstone reservoir at about 1 km depth with 39°C warm, highly saline fluid. The geothermal system delivers 41 MWth. Since start of injection in 2001, rates constantly decrease in both injection wells. Several treatments have been used to enhance the injectivity. However, those applications have not yet resolved injectivity decrease. Thus, we applied a new approach incorporating all relevant processes and adjusting the scenarios based on multidisciplinary observations. Most potential scenarios at the Klaipeda site are ranked based on a Feedback Adjustment Procedure. Most probably reasons for injectivity problems at the site are clogging of filter screen and/or pores by precipitation of minerals, by corrosion-particles, by biofilm, by injection of finest particles or pollution by drilling mud. In a next step, borehole logs, camera inspection and production and injection tests will be used to further rank scenarios. Specific stimulation treatments will be selected after re-evaluation for each scenario. Precipitations and biofilm will be removed and lifted by chemical-mechanical cleaning. Finest particles and corrosion material will be removed by long-term production tests. A mud cake will be hydraulically stimulated with frac-packs. Any new observation requires a re-evaluation and ordering of scenarios based on updated database. Therefore, the Feedback Adjustment Procedure will guarantee a sustainable overcome of formation damage.

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