가스하이드레이트 해리에 따른 해저지반의 역학적 변형 해석
Numerical Analysis for Geomechanical Deformation of Sea Bed due to Gas Hydrate Dissociation
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초록
본 연구에서는 수치해석을 통해 가스하이드레이트 함유층 내 초기응력분포 및 가스 생산을 위한 감압압력이 해저 지반의 역학적 변형에 미치는 영향을 살펴보았다. 해석기법으로는 가스하이드레이트의 해리 및해리 가스와 공극 유체의 열유동뿐만 아니라 주변 지반 내 응력 및 변형을 동시에 시뮬레이션할 수 있는TOUGH+Hydrate와 FLAC3D를 순차해석하는 방식을 사용하였다. 동해 울릉분지 시추조사 결과에 근거한 기존해석사례(Lim, 2013; Moridis et al., 2013)를 이용한 모델 해석 결과, 침하는 균등한 양상으로 발생하였으며, 침하량은 해저 지반의 강성 특성에 매우 민감한 반응을 보였다. 수평응력에 비해 수직응력이 우세한 이방성응력조건에서 침하량이 다소 증가하는 결과를 보였으며 초기응력분포보다 감압 시 공저 압력 수준에 상대적으로민감한 결과를 보였다. 가스하이드레이트 해리에 따른 상부 지층 및 주변 해저 지반의 유효 응력 변화에 의한전단파괴는 일어나지 않는 것으로 예측되었다.
Abstract
In this study, we examined the influence of in-situ stress and bottom hole pressure on dissociation-induced geomechanical deformation of hydrate-bearing formation in a numerical manner. The sequentially coupled analysis of TOUGH+Hydrate and FLAC3D was employed for the simulation of hydrate dissociation and subsequent dissociated gas flow as well as stress/deformation analysis of the surrounding formations, respectively. The simulation model was constructed using the information of the Ulleung basin from the recently published work (Lim, 2013; Moridis et al., 2013). We could observe that subsidence may occur in a homogeneous way and was sensitive to stiffness properties of sea beds. The subsidence was more substantial when initial stress condition is anisotropic, but depressurization level at the bottom hole was more influential to the subsidence rather than the initial stress condition. The potential for shear failure in hydrate-bearing formation and surrounding ground induced by effective stress change was predicted to be little.
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