Fluid extraction from sandstone oil, gas, or geothermal reservoirs causes elastic and inelastic compaction of the reservoir, which may lead to surface subsidence and induced seismicity, as observed in the Groningen Gas Field, Netherlands. The inelastic compaction is partly caused by rate- or time-dependent processes, meaning that compaction may continue even if production is stopped. To reliably evaluate the impact of prolonged reservoir exploitation and post-abandonment behavior (>10–100 years), mechanism-based rate/time-dependent compaction laws are needed. We systematically investigated the effect of strain rate (rates of 10−3–10−9 s−1) in triaxial compression experiments performed on clay-bearing Bleurswiller sandstone (as an analogue of the Groningen reservoir sandstone) and almost clay-free Bentheimer sandstone, to explore the effect of mineralogy. Our results showed a systematic lowering of stress–strain curves with decreasing axial strain rate in Bleurswiller sandstone at differential stresses exceeding 40%–50% of peak stress (i.e. comparable to typical reservoir stress conditions). By contrast, in Bentheimer sandstone, rate effects were only noticeable at differential stresses > 70% of peak differential stress. Further investigation of the deformation behavior of Bleurswiller sandstone at varying confining pressure, temperature and pore fluid pH, complemented by microstructural analysis, suggested that the observed rate effects are likely controlled by rate-dependent intergranular frictional sliding at lower differential stress, with an increased role of stress corrosion cracking at higher stress. Extrapolation of our data to reservoir conditions suggests that additional strains of about 10% can be expected, compared to the strain accumulated at laboratory strain rates. Our results show that time-dependent inelastic deformation plays an important role in controlling reservoir deformation, such as of the Groningen gas reservoir. Such effects could lead to an underestimation of surface subsidence and induced seismicity, if not accounted for. The present experiments provide important data for developing physics-based constitutive models for predicting rate/time-dependent reservoir compaction.

中文翻译：

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应变速率对储集层条件下变形多孔砂岩非弹性应变发展的影响


从砂岩石油、天然气或地热储层中提取流体会导致储层的弹性和非弹性压实，这可能导致地表沉降和诱发地震，如在荷兰格罗宁根气田观察到的那样。非弹性压实部分是由速率或时间相关的过程引起的，这意味着即使停止生产，压实也可能继续。为了可靠地评估长期储层开采和弃化后行为（x3E10-100 年）的影响，需要基于机制的速率/时间依赖性压实定律。我们系统地研究了在对含粘土的 Bleurswiller 砂岩（作为格罗宁根储层砂岩的类似物）和几乎不含粘土的 Bentheimer 砂岩进行的三轴压缩实验中应变率（速率为 10-3-10-9 s-1）的影响，以探索矿物学的影响。我们的结果表明，在差异应力超过峰值应力的 40%-50%（即与典型的储层应力条件相当）时，Bleurswiller 砂岩的应力-应变曲线随着轴向应变率的降低而系统地降低。相比之下，在 Bentheimer 砂岩中，速率效应仅在峰值差应力的 > 70% 的差应力下才明显。对 Bleurswiller 砂岩在不同围压、温度和孔隙流体 pH 值下的变形行为的进一步研究，辅以微观结构分析，表明观察到的速率效应可能由较低差应力下速率依赖性的晶间摩擦滑动控制，在较高应力下应力腐蚀开裂的作用增加。 将我们的数据外推到储层条件表明，与在实验室应变速率下积累的菌株相比，可以预期会增加约 10% 的菌株。我们的结果表明，瞬态非弹性变形在控制储层变形中起着重要作用，例如格罗宁根气藏。如果不加以考虑，这些影响可能会导致低估地表沉降和诱发地震。本实验为开发基于物理的本构模型提供了重要数据，用于预测速率/时间依赖性的储层压实。