| 講演要旨(和文) | | 水圧破砕法 (Hydraulic Fracturing)は、ボーリング孔に流体を注入することで地盤中に亀裂を形成する手法である。しかし、水圧破砕に伴う環境問題も発生しており、より安全で効率の良い水圧破砕の適用のために、坑井内に流体を圧入した際の亀裂の発生場所や、応力場の変化による既存の亀裂の伸展を数値的にシミュレーションすることが不可欠である。本研究では、水圧破砕に伴う地盤中の応力場の変化や破壊現象に対して原位置地圧やボアホール周辺の既存の亀裂が与える影響に着目し、拡張有限要素法(X-FEM) を用いてこれらの問題を取り扱うことにした。拡張有限要素法を用いることにより亀裂の伸展とともに変化する応力分布を効率よく求めることができ、その結果円孔周りの応力集中や孔隙水圧の変化と亀裂伸展方向の関係を求めることができた。本研究の結果は、水圧破砕法を行う上での応力場の推定や亀裂進展の推定に適用できる。 |
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| | 講演要旨(英文) | | It is well known that the hydraulic fracturing is a tool commonly used for stimulating hydrocarbon reservoirs, and in-situ stress measurement. It is, however, difficult to predict the behavior of fracture propagation from boreholes due to the difficulty to estimate stress distribution in the subsurface. We have developed a program to simulate fracture propagation from a borehole due to increasing fluid pressure. We employed an extended finite element method (X-FEM), which deals with any fractures independent from the location of grid or mesh in the numerical simulation. We first found that our program could simulate that the local stress field near the borehole showed some deviated orientation from the regional stress field. We then confirmed that the tendency of fracture propagations to be a function of fluid pressure to induce the extension of fracture. The orientation of the fracture propagation converges to that of the principal stress. However, the higher the fluid pressure is, the smaller the curvature of fracture trace becomes. We would like to conclude that the orientation of maximum in-situ principal stress and the fluid pressure for fracturing is two major parameters to control the propagation of fractures due to increasing fluid pressure. |
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