Intergranular Clay Films Control Inelastic Deformation in the Groningen Gas Reservoir: Evidence From Split‐Cylinder Deformation Tests
Intergranular Clay Films Control Inelastic Deformation in the Groningen Gas Reservoir: Evidence From Split‐Cylinder Deformation Tests
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DOI：
10.1029/2019jb018702
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发表时间：
2019-12
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影响因子：
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通讯作者：
R. Pijnenburg;B. Verberne;S. Hangx;C. Spiers
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文献类型：
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作者：
R. Pijnenburg;B. Verberne;S. Hangx;C. Spiers
砂岩储层的油气开采导致储层产生较小的弹性和非弹性应变，这可能引起地面沉降和地震活动。虽然弹性分量很容易描述，但在相关的小应变范围内（≤1.0%），非弹性分量及其任何速率敏感性仍然知之甚少。为了解决这个问题，我们对格罗宁根发震气田Slochteren砂岩的单个裂柱样品（孔隙度20.4%）进行了5次应力/应变循环加应变标记成像实验。试验是在有效围压（40 MPa）和温度（100℃）的原位条件下进行的，在连续运行中探索了越来越大的差应力（高达75 MPa）和/或轴向应变（高达4.8%）。在与产储层相关的小应变（≤1.0%）下，非弹性变形在很大程度上由粘土充填颗粒接触的变形所调节。高轴向应变（>1.4%）导致普遍的晶内裂纹和局部共轭带内的晶间滑移。使用简化的砂岩模型，我们表明，在小应变（≤1.0%）和与格罗宁根储层相关的应力下，我们的实验产生的非弹性变形的大小确实可以大致地用粘土膜变形来解释。因此，预计格罗宁根储层的非弹性压实在很大程度上受粘土膜变形的控制。这种机制的压实对生产时间尺度的速率不敏感，预计当天然气生产停止时，压实就会停止。然而，其他工艺的蠕变不能消除。同样，含粘土砂岩储层在全球范围内广泛存在，这意味着我们的结果具有广泛的相关性。
Production of oil and gas from sandstone reservoirs leads to small elastic and inelastic strains in the reservoir, which may induce surface subsidence and seismicity. While the elastic component is easily described, the inelastic component, and any rate‐sensitivity thereof remain poorly understood in the relevant small strain range (≤1.0%). To address this, we performed a sequence of five stress/strain‐cycling plus strain‐marker‐imaging experiments on a single split‐cylinder sample (porosity 20.4%) of Slochteren sandstone from the seismogenic Groningen gas field. The tests were performed under in situ conditions of effective confining pressure (40 MPa) and temperature (100 °C), exploring increasingly large differential stresses (up to 75 MPa) and/or axial strains (up to 4.8%) in consecutive runs. At the small strains relevant to producing reservoirs (≤1.0%), inelastic deformation was largely accommodated by deformation of clay‐filled grain contacts. High axial strains (>1.4%) led to pervasive intragranular cracking plus intergranular slip within localized, conjugate bands. Using a simplified sandstone model, we show that the magnitude of inelastic deformation produced in our experiments at small strains (≤1.0%) and stresses relevant to the Groningen reservoir can indeed be roughly accounted for by clay film deformation. Thus, inelastic compaction of the Groningen reservoir is expected to be largely governed by clay film deformation. Compaction by this mechanism is shown to be rate insensitive on production timescales and is anticipated to halt when gas production stops. However, creep by other processes cannot be eliminated. Similar, clay‐bearing sandstone reservoirs occur widespread globally, implying a wide relevance of our results.