The existence of a deep borehole in the Earth’s crust disturbs the local stresses and creates a stress concentration that may result in breakout and damage to the borehole. Maintaining wellbore integrity mitigates environmental impacts such as groundwater contamination, gas leakage to the atmosphere, and fluid spills and seepage at the surface. In this paper, the stability of deep boreholes (5 km) is examined by laboratory experiments and numerical models in the context of nuclear waste disposal in Israel. Two rock types in southern Israel are considered: the crystalline basement (granite) and the Zenifim Formation (arkose). A series of room-temperature triaxial rock deformation experiments were conducted at different confining pressures. This mechanical characterization was then used to parameterize the elastic properties and damage behavior of the rocks. This facilitated modeling the stability of the deep boreholes by two different formulations of damage rheology: a dynamic-oriented formulation used to model deformation immediately after the creation of the open hole and a quasi-static formulation used to model longer stress corrosion regime. The calibrated modeling results indicate greater stability with Zenifim arkose than the crystalline granite for deep borehole conditions despite the granite having a greater triaxial compressive strength. Dissipation associated with dilation and porous compaction in the arkose during deformation plays a significant stabilizing role in the borehole compared to crystalline rocks. These results suggest that common strength-based borehole stability assessment may lead to inaccurate predictions. Three-dimensional modeling of bottom-hole stress conditions and the effects of transient borehole geometry show conventional two-dimensional analysis may not be conservative when predicting borehole damage.

地壳中存在一个深孔，这会扰乱局部应力并产生应力集中，这可能会导致钻孔破裂和损坏。保持井筒的完整性可以减轻环境影响，例如地下水污染，气体向大气的泄漏以及流体的溢出和地表渗漏。在本文中，在以色列进行核废料处理的情况下，通过实验室实验和数值模型检验了深孔（5公里）的稳定性。考虑了以色列南部的两种岩石类型：结晶基底（花岗岩）和Zenifim地层（黑糖）。在不同的围压下进行了一系列室温三轴岩石变形实验。然后使用这种机械特性来参数化岩石的弹性和破坏行为。这有助于通过两种不同的损伤流变公式对深孔的稳定性进行建模：一种用于动态模型，用于在裸眼创建后立即对变形进行建模；以及一种用于模拟较长应力腐蚀状态的准静态模型。校准的模型结果表明，即使花岗岩具有更高的三轴抗压强度，Zenifim arkose仍比深层钻孔条件下的结晶花岗岩具有更高的稳定性。与结晶岩相比，变形过程中与阿科斯膨胀和多孔压实有关的耗散在井眼中起着重要的稳定作用。这些结果表明，基于强度的常见井眼稳定性评估可能导致不准确的预测。井底应力条件的三维建模和瞬态井眼几何形状的影响表明，常规的二维分析在预测井眼破坏时可能并不保守。