인공저류층 지열시스템 운영 중 지열수 플러싱 공정의 지화학적 영향
Geochemical Effect of Geothermal Water Flushing during Enhanced Geothermal Systems Operation
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인공저류층 지열시스템(EGS) 운영 중 생길 수 있는 대표적인 문제점은 스케일의 생성인데 여러 주변 환경 조건으로부터 영향을 받는다. 파이프 또는 저류층 내에서 생기는 스케일 물질로 인하여 주입정과 생산정의 직경이 좁아지거나 저류층의 투수성이 줄어들어 EGS의 효율성을 낮추게 된다. 낮아진 효율을 회복하기 위한 방법 중의 하나로 EGS 운영 중 지열수 플러싱이 적용될 수 있다. 본연구에서는 EGS 모사 실험장치를 이용하여 수리자극 중 EGS 저류층 내 암석의 광물 조성 변화와순환수의 화학조성 변화를 관찰하였다. EGS를 모사하기 위하여 지열수를 여러 번 순환하여 균열된 코어에 투과시키는 실험이 진행되었다. 실험결과에 의하면 지열수 내의 Si 이온이 감소하고 균열 내 형성되는 침전으로 투수율이 감소하였다. 이를 해결 하기 위하여 더 높은 압력으로 지표수를사용하여 플러싱을 실험적으로 적용시킬 때 침전된 광물이 용해되는 결과를 확인하였다.
Abstract
Scale production occurs during enhanced geothermal system (EGS) processes due to various conditions. The production of scales in pipes or fractured reservoir narrows the diameter of the injection and production well, decreasing permeability and reducing EGS efficiency. However, geothermal water flushing during EGS processes can be implemented to recover the permeability. In this study, an experimental instrument to simulate a geothermal system was applied to observe the chemical composition change of core and water samples. To simulate the EGS, an experiment was conducted by injecting the geothermal fluid in several cycles to the fractured core. Results showed that Si ions decreased in the geothermal fluid and permeability decreased due to precipitation. Thereafter, flushing was applied, and dissolution occurred inside the fracture, increasing the permeability.
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