Abstract

A pre-existing plane of weakness along the fault is comprised of a particular pattern of joints dipping at different orientations. The fault stress state, partially defined by the orientation of fault, determines the potential of slip failure and hence the evolution of fault permeability. Here the influence of fault orientation on permeability evolution was investigated by direct fluid injection inside fault with three different sets of fault orientations (45°, 60° and 110°), through the coupled hydromechanical (H-M) model TOUGHREACT-FLAC3D. The influence of joints pattern on slip tendency and magnitude of potential induced seismicity was also evaluated by comparing the resulted slip distance and timing. The simulation results revealed that decreasing the dip angle of the fault increases the corresponding slip tendency in the normal fault circumstance. Also, with changing joints dip angle associated with the fault, the tendency of the fault slip changes concurrently with the permeability evolution in a noticeable manner. Permeability enhancement after the onset of fault slip was observed with the three sets of fault angles, while the condition of 60° dipping angle resulted in highest enhancement. Joints pattern with a dip angle of 145° (very high dip) and 30° (very low dip) did not trigger a shear slip with seismic permeability enhancement. However, high dip and intermediate dip angles (135°, 50° and 70°) yielded high permeability in varying orders of magnitude. The large stress excitation and increasing permeability during shear deformation was noticeably high in intermediate joint dip angles but decreases as the angle increases.

Article highlights

1. 1.

   The magnitude of injection-induced permeability enhancement is largely influenced by the fault and joint spatial orientations.

2. 2.

   With a slight change in the joint direction, there is an increasing possibility for fault to approach a different critical state of failure.

3. 3.

   Stress elevation at the point of failure is controlled by the orientations of fault/joint planes with respect to the direction of maximum principal stress.

中文翻译：

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不连续性取向对断层渗透率演化和滑动位移影响的数值研究

摘要

沿断层先前存在的弱化面由在不同方向上浸入的特定接头模式组成。断层的应力状态（部分由断层的方向确定）决定了滑动破坏的可能性，并因此决定了断层渗透率的演变。在这里，通过耦合流体力学（HM）模型TOUGHREACT-FLAC3D，通过在三个不同断层方向（45°，60°和110°）的断层内部直接注入流体，研究了断层方向对渗透率演化的影响。通过比较所得的滑移距离和时间，还评估了节理型式对滑移趋势和潜在诱发地震活动度的影响。仿真结果表明，在正常断层情况下，减小断层的倾角会增加相应的滑动趋势。而且，随着与断层相关的节理倾角的变化，断层滑动的趋势与渗透率的演变同时发生显着变化。在三组断层角下均观察到断层滑动开始后的渗透性增强，而在倾角为60°的条件下渗透率得到了最大的增强。倾角为145°（非常高的倾角）和30°（非常低的倾角）的节型不会触发剪切滑移，从而增强了地震渗透率。但是，高倾角和中间倾角（135°，50°和70°）会产生不同数量级的高磁导率。

文章重点

1. 1。

   注入引起的渗透率增强的幅度在很大程度上受断层和关节空间方位的影响。

2. 2。

   随着关节方向的轻微变化，故障越来越有可能进入不同的关键故障状态。

3. 3。

   破坏点处的应力升高由断层/接合面相对于最大主应力方向的方向控制。