Tunnel and Underground Space (터널과지하공간)

Korean Society for Rock Mechanics and Rock Engineering (한국암반공학회)
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Influence of the Cleavage Anisotropy of Pocheon Granite on Hydraulic Fracturing Behaviour

포천 화강암의 결 이방성이 수압파쇄거동에 미치는 영향

  • 정성규 (과학기술연합대학원대학교(UST) 지반신공간공학과) ;
  • 장리 (한국건설기술연구원 지반연구소) ;
  • 염선 (한국건설기술연구원 지반연구소) ;
  • 김광염 ;
  • 민기복 (서울대학교 에너지시스템공학부)
  • Received : 2016.08.17
  • Accepted : 2016.08.29
  • Published : 2016.08.31
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Abstract

In this study, laboratory hydraulic fracturing tests are carried out to evaluate the effects of the cleavage anisotropy of Pocheon granite. Breakdown pressure is smaller when cracks are generated to the direction of rift plane in constant pressurization rate condition because of higher microcracks density. Besides not only injection rate changes but also the amount of injection pressure for fracture initiation and crack expansion is detected while testing due to internal deformation. Pressurization rate is higher while hydraulic fracture testing with constant injection rate condition in case of the specimen which has rift plane perpendicular to borehole because there are much flow paths to penetrate compared to the specimen which has hardway plane perpendicular to borehole. Observation by X-ray CT scanning shows that almost all of cracks due to hydraulic fracturing are generated to the direction of plane which has higher microcrack density that is rift plane or grain plane.

본 연구에서는 화강암 내부의 미세균열 분포에 따른 이방성이 수압파쇄실험 결과에 미치는 영향을 평가하였다. 압력증가율을 일정하게 설정하여 수압파쇄실험을 수행한 결과, 원주방향(주입정 방향과 직교)으로 리프트면이 분포한 시료의 파쇄압력이 가장 낮게 측정되었고, 이는 미세균열의 밀도가 높기 때문이다. 수압파쇄실험과정에서 시료 내부의 변화가 발생하는 주입압력의 크기와 유체 주입속도의 변화 또한 결방향에 따라 분포한 미세균열의 밀도와 관계가 있는 것으로 판단된다. 유체주입속도를 일정하게 설정하여 수압파쇄실험을 수행하였을 경우, 상대적으로 미세균열의 밀도가 높은 리프트면이 원주방향으로 분포된 시료에서 주입압력증가율이 낮게 나타났고, 유체가 침투될 수 있는 균열망이 상대적으로 적게 형성된 그레인면 및 하드웨이면이 원주방향으로 분포된 시료에서는 압력증가율이 높게 나타났다. X-ray CT 촬영을 통해 시료 내부에 생성된 균열의 방향을 확인한 결과, 대부분의 시료에서 리프트면 혹은 그레인면과 평행한 방향으로 균열이 생성된 것을 확인하였고, 이는 암석 내에 상대적으로 미세균열의 밀도가 높아서 분리성이 크기 때문이다.

Keywords

References

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