Tunnel and Underground Space (터널과지하공간)

Korean Society for Rock Mechanics and Rock Engineering (한국암반공학회)
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Experimental Study on Fracture Pressure, Permeability Enhancement and Fracture Propagation using Different Fracture Fluids

다양한 파쇄 유체별 파쇄압력, 투과도 증진 및 균열전파에 관한 실험적 연구

  • Choi, JunHyung (Korea Institute of Geoscience and Mineral Resources Post Doc. Oil & Gas Research Center) ;
  • Lee, Hyun Suk (Korea Institute of Geoscience and Mineral Resources Post Doc. Oil & Gas Research Center) ;
  • Kim, Do Young (Department of Energy and Mineral Resources Engineering, Dong-A University) ;
  • Nam, Jung Hun (Department of Energy and Mineral Resources Engineering, Dong-A University) ;
  • Lee, Dae Sung (Department of Energy and Mineral Resources Engineering, Dong-A University)
  • 최준형 (한국지질자원연구원 석유가스연구센터) ;
  • 이현석 (한국지질자원연구원 석유가스연구센터) ;
  • 김도영 (동아대학교 에너지.자원공학과) ;
  • 남정현 (동아대학교 에너지.자원공학과) ;
  • 이대성 (동아대학교 에너지.자원공학과)
  • Received : 2021.01.25
  • Accepted : 2021.02.10
  • Published : 2021.02.28
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Abstract

The hydraulic fracturing developed to improve permeability of tight reservoir is one of key stimulation technologies for developing unconventional resources such as shale gas and deep geothermal energy. The experimental study was conducted to improve disadvantage of hydraulic fracturing which has simple fracture pattern and poor fracturing efficiency. The fracturing experiments was conducted for tight rock using various fracturing fluids, water, N2, and CO2 and the created fracture pattern and fracturing efficiency was analyzed depending on fracturing fluids. The borehole pressure increased rapidly and then made fractures for hydraulic fracturing with constant injection rate, however, gas fracturing shows slowly increased pressure and less fracture pressure. The 3D tomography technic was used to generate images of induced fracture using hydraulic and gas fracturing. The stimulated reservoir volume (SRV) was estimated increment of 5.71% (water), 12.72% (N2), and 43.82% (CO2) respectively compared to initial pore volume. In addition, permeability measurement was carried out before and after fracturing experiments and the enhanced permeability by gas fracturing showed higher than hydraulic fracturing. The fracture conductivity was measured by increasing confining stress to consider newly creating fracture and closing induced fracture right after fracturing. When the confining stress was increased from 2MPa to 10MPa, the initial permeability was decreased by 89% (N2) and 50% (CO2) respectively. This study shows that the gas fracturing makes more permeability enhancement and less reduction of induced fracture conductivity than hydraulic fracturing.

치밀 저류층의 투과도 증진을 위해 개발된 수압파쇄 기술은 셰일가스와 같은 비전통자원과 심부지열 개발에 필수적인 기술 중 하나이다. 파쇄형태가 단순하고 파쇄효율이 좋지 않은 수압파쇄를 개선하기 위해 다양한 파쇄유체를 이용한 실험적 연구가 진행되었다. 물, N2, CO2 가스를 파쇄유체로 사용하여 치밀 암석에 대한 파쇄형태와 효율성을 분석하였다. 파쇄유체로 물을 일정 주입속도로 주입한 경우 순간적으로 압력이 상승하여 파쇄가 발생하였으나, 파쇄유체로 가스를 주입한 경우 서서히 압력이 증가되면서 물보다 낮은 파쇄압력을 보였다. 3D 단층촬영 기법을 이용하여 물과 가스 주입으로 생성된 균열을 관찰한 결과는 기존 공극부피 대비 파쇄 자극부피가 각각 5.71%(물), 12.72%(N2), 43.82%(CO2) 증가되었다. 또한 파쇄유체의 파쇄 효율성을 검정하기 위한 파쇄 전후 투과도 변화 실험에서는 가스 파쇄에 의해 증가되는 투과도 증가 값이 물을 이용한 파쇄보다 훨씬 높게 측정되었다. 파쇄 이후 인공균열의 생성과 주변응력에 의해 다시 균열이 닫히는 현상을 고려하여 생성된 인공균열에 구속압을 단계별로 증가시켜 투과도 변화를 측정하였다. 구속압이 2MPa에서 10MPa로 증가시켰을 경우 초기 투과도 대비 각각 89%(N2), 50%(CO2) 감소하였다. 본 연구는 가스파쇄기술이 수압파쇄보다 투과도 증진 효과가 크고 이후 주변 응력에 의한 투과도 감소가 적은 것으로 나타났다.

Keywords

Acknowledgement

이 논문은 한국지질자원연구원의 '국내 대륙붕3차원 석유시스템 평가 및 셰일가스전 EGR+ 원천기술 개발(GP 2020-006)' 연구와 정부(과학기술정보통신부)의 재원으로 한국연구재단의 지원을 받아 수행된 연구임(No. NRF-2020R1F1A1063305).

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