Laboratory experimental study on fracture shear-activation induced by carbon dioxide injection

국문 초록 (Abstract)

대표적 이산화탄소 지중저장 저류암인 사암에 이산화탄소를 주입시 사암 내 균열의 거동과 전단활성을 유발하는 임계 압력조건을 분석하기 위한 실내 실험을 수행하였다. 인공적으로 임의의 각도로 기울어진 균열면을 형성시킨, 물로 포화된 Berea 사암시편에 삼축압축 응력조건 하에서 이산화탄소를 단계적으로 주입하여 균열의 전단활성을 유도하였다. 실험을 통해 측정된 균열 전단활성을 유발시키는 임계공극압을 쿨롱마찰법칙을 통해 유추한 이론적 임계공극압과 비교하였다. 모든 실험에서 균열의 전단활성은 이론적으로 유추한 임계공극압보다 최소 8%, 최대 133% 이상 높은 공극압에서 발생하였다. 이 결과는 물로 포화된 사암 내 이산화탄소를 주입시 공극압 증가에 따른 단순한 역학적 변화를 초래하는 것 이상의 물-이산화탄소-암석 간의 화학적 상호작용에 의한 물성 변화가 있음을 암시한다. 이를 확인하기 위한 방법으로 이산화탄소와 물로 동시에 포화된 사암시편에 대해 균열 전단 물성을 측정해 보니 물과 이산화탄소로 포화된 시편 내 균열의 점착력은 단순히 물로만 포화된 균열의 점착력 보다 높아 있음을 확인하였다. 즉, 물, 이산화탄소, 암석 간의 상호작용에 의한 균열 강화가 진행된다는 점을 의미하며 이는 이산화탄소 주입, 운영에 있어 호의적인 측면으로 작용한다.

다국어 초록 (Multilingual Abstract)

We investigated critical pore pressures that could trigger shearing along a fracture when we injected carbon dioxide into water-saturated Berea sandstone. We gradually increased pore pressure by injecting CO₂ into cylindrical sandstone specimens containing a saw-cut fracture subjected to triaxial compression. Shearing along fracture occurred when pore pressure reached a critical value higher by 8-133% of that theoretically predicted by the Coulomb friction law. This result suggests a water-CO₂-rock interaction leading to an enhancement of shear strength of fracture, which may be best described as a chemical-mechanical coupling. To confirm this inference, we conducted another series of tests, in which the same specimens saturated with both water and CO₂ were loaded under triaxial compression to determine frictional properties of the fractures, and found that the cohesion of fractures increased above that of water-saturated samples. Thus, such a strengthening effect of water-CO₂-rock interaction on fracture can work favorably in CO₂ sequestration projects.

목차 (Table of Contents)

• 요약
• ABSTRACT
• 1. 서론
• 2. 이론적 배경
• 3. 시험시편 및 마찰계수 측정
• 4. 이산화탄소 주입실험 및 결과
• 5. 이산화탄소 주입에 의한 균열 마찰물성 변화
• 6. 결론
• REFERENCES

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