Hunfeld Luuk B, Chen Jianye, Hol Sander, Niemeijer André R, Spiers Christopher J
HPT Laboratory, Department of Earth Sciences Utrecht University Utrecht The Netherlands.
Rock and Fluid Science Shell Global Solutions International B.V. Amsterdam The Netherlands.
J Geophys Res Solid Earth. 2020 Jul;125(7):e2019JB018790. doi: 10.1029/2019JB018790. Epub 2020 Jun 26.
We investigated the frictional strength recovery (healing) and subsequent reactivation and slip-weakening behavior of simulated fault gouges derived from key stratigraphic units in the seismogenic Groningen gas field (N. E. Netherlands). Direct-shear, slide-hold-slide (SHS) experiments were performed at in situ conditions of 100 °C, 40 MPa effective normal stress and 10-15 MPa pore fluid pressure (synthetic formation brine). Sheared gouges were allowed to heal for periods up to 100 days before subsequent reshearing. The initial coefficient of (steady) sliding friction was highest in the Basal Zechstein caprock ( = 0.65 ± 0.02) and Slochteren sandstone reservoir ( = 0.61 ± 0.02) gouges, and the lowest in the Ten Boer claystone at the reservoir top ( = 0.38 ± 0.01) and in the Carboniferous shale substrate ( ≈ 0.45). Healing and subsequent reactivation led to a marked increase () in (static) friction coefficient of up to ~0.16 in Basal Zechstein and ~0.07 in Slochteren sandstone gouges for the longest hold periods investigated, followed by a sharp strength drop (up to ~25%) and slip-weakening trajectory. By contrast, the Ten Boer and Carboniferous gouges showed virtually no healing or strength drop. Healing rates in the Basal Zechstein and Slochteren sandstone gouges were significantly affected by the stiffness of different machines used, in line with the Ruina slip law, and with a microphysical model for gouge healing. Our results point to marked stratigraphic variation in healed frictional strength and healing rate of faults in the Groningen system, and high seismogenic potential of healed faults cutting the reservoir and Basal Zechstein caprock units, upon reactivation.
我们研究了源自格罗宁根气田（荷兰东北部）关键地层单元的模拟断层泥的摩擦强度恢复（愈合）以及随后的再活化和滑动弱化行为。在100°C、40MPa有效法向应力和10 - 15MPa孔隙流体压力（合成地层盐水）的原位条件下进行了直剪、滑-停-滑（SHS）实验。在后续重新剪切之前，让剪切后的断层泥愈合长达100天。初始（稳态）滑动摩擦系数在基底蔡希斯坦盖层（= 0.65 ± 0.02）和斯洛赫特伦砂岩储层（= 0.61 ± 0.02）断层泥中最高，而在储层顶部的滕布尔粘土岩（= 0.38 ± 0.01）和石炭系页岩基底（≈ 0.45）中最低。愈合和随后的再活化导致基底蔡希斯坦断层泥的（静态）摩擦系数显著增加（），在研究的最长保持时间内增加到约0.16，在斯洛赫特伦砂岩断层泥中增加到约0.07，随后强度急剧下降（高达约25%）并出现滑动弱化轨迹。相比之下，滕布尔和石炭系断层泥几乎没有愈合或强度下降。基底蔡希斯坦和斯洛赫特伦砂岩断层泥的愈合速率受所用不同机器刚度的显著影响，这与瑞纳滑动定律以及断层泥愈合的微观物理模型一致。我们的结果表明，格罗宁根系统中断层的愈合摩擦强度和愈合速率存在显著的地层变化，并且在再活化时，切割储层和基底蔡希斯坦盖层单元的愈合断层具有高地震潜力。
