在許多天然氣及石油場域中經常會遇到井壁穩定性問題，岩盤應力會因開挖而不斷的重新分布，因此在鑽井時，為了保持其井壁的穩定性，必須充分考慮岩體內的裂隙，以及隨著水平大地主應力不同時可能對井壁穩定帶來的負面影響。本研究透過UDEC（Universal Distinct Element Code）程式進行數值模擬，分析於破裂岩體中井壁之應力分布狀態，並比對同樣彈性行為之數值結果。本研究採任意多邊型和兩組節理排列之五種節理型式，以及三種不同水平大地作用力狀態來模擬在不同水平大地應力狀態下井壁應力分布狀況。另外，改變節理間距，進行不同節理間距對井壁行為影響之研究；以及模擬改變井壁壓力對其周圍節理內之流速、孔隙水壓之影響。數值分析結果顯示井壁的節理會隨著水平大地應力相差越多而更加惡化；節理的間距和塊體幾何形狀也是井壁穩定的重要控制因素；而施加井壁壓力的鑽井泥漿，在設計其密度時，應考慮到節理型式及原處之大地壓力狀態。

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