Abstract Fault reactivation may lead to induced seismicity, damage to wells and loss of containment of potentially harmful and economically valuable fluids or gas in the subsurface. For this reason, fault reactivation is assessed in hydrocarbon development projects, in particular when injecting water, gas, or steam, but also when disposing of (contaminated) water or CO2 in depleted oil or gas reservoirs. In this paper, we compare the results obtained by a Mohr-circle evaluation and two-dimensional Finite-Element (FE) analysis that are commonly used to assess the likelihood of fault reactivation. It is found that Mohr-circle evaluations provide a non-conservative estimate of the allowable reservoir pressure in cases where the reservoir is offset by a fault. In practice, this may comprise virtually all imageable faults, as the limited seismic resolution does not allow interpretation of faults with no or small throws. Furthermore, we demonstrate that the maximum (vertical) element size for capturing the onset of fault slip with sufficient accuracy is about 2% of the reservoir thickness. Finite-element models with larger vertical element size increasingly over-estimate the depletion pressure required to cause fault reactivation or won't predict fault reactivation at all, thereby under-estimating the hazard associated with fault reactivation. This paper concludes with recommendations for evaluating onset of fault slip using Mohr-circles, and two- and three-dimensional finite-element analysis.

中文翻译：

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为什么莫尔圆分析可能会低估枯竭油藏断层再激活的风险

摘要 断层再激活可能导致诱发地震活动、对井的破坏以及对地下潜在有害且具有经济价值的流体或气体的遏制能力丧失。出于这个原因，在碳氢化合物开发项目中评估断层再活化，特别是在注入水、气体或蒸汽时，以及在枯竭的油藏或气藏中处理（受污染的）水或 CO2 时。在本文中，我们比较了通常用于评估故障再激活可能性的莫尔圆评估和二维有限元 (FE) 分析所获得的结果。发现在储层被断层偏移的情况下，莫尔圆评估提供了允许储层压力的非保守估计。实际上，这可能包括几乎所有可成像的故障，因为有限的地震分辨率不允许解释没有或小断层的断层。此外，我们证明了用于以足够精度捕获断层滑动开始的最大（垂直）单元尺寸约为储层厚度的 2%。具有较大垂直单元尺寸的有限元模型越来越高估导致断层再激活所需的耗尽压力，或者根本无法预测断层再激活，从而低估了与断层再激活相关的危险。本文最后提出了使用莫尔圆以及二维和三维有限元分析评估断层滑动开始的建议。我们证明，用于以足够精度捕获断层滑动开始的最大（垂直）单元尺寸约为储层厚度的 2%。具有较大垂直单元尺寸的有限元模型越来越高估导致断层再激活所需的耗尽压力，或者根本无法预测断层再激活，从而低估了与断层再激活相关的危险。本文最后提出了使用莫尔圆以及二维和三维有限元分析评估断层滑动开始的建议。我们证明，用于以足够精度捕获断层滑动开始的最大（垂直）单元尺寸约为储层厚度的 2%。具有较大垂直单元尺寸的有限元模型越来越高估导致断层再激活所需的耗尽压力，或者根本无法预测断层再激活，从而低估了与断层再激活相关的危险。本文最后提出了使用莫尔圆以及二维和三维有限元分析评估断层滑动开始的建议。从而低估了与故障重新激活相关的危险。本文最后提出了使用莫尔圆以及二维和三维有限元分析评估断层滑动开始的建议。从而低估了与故障重新激活相关的危险。本文最后提出了使用莫尔圆以及二维和三维有限元分析评估断层滑动开始的建议。