Role of Deep Fluid Injection in Induced Seismicity in theDelaware Basin, West Texas and Southeast New Mexico

特拉华盆地的地震活动率从2017年的每年10次本地震级（ML）3.0及以上增加到2022年的超过185次，这一增长与油气生产和废水回注到生产层位浅层或深层地层的活动相吻合。迄今为止，最大震级达到ML 5.4的地震事件发生在延伸到接收了超过四十亿桶注入的基底以上的地层中的断层上。

在这里，我们展示了该区域注入地质学、孔隙压力演化、断层稳定性和诱发地震之间的联系。我们发现，注入目标主要是具有低（<5体积%）基质孔隙度和由裂缝增强渗透性的白云岩化平台碳酸盐岩，这些岩石在流动属性上具有固有的非均质性。我们使用一个全面的三维地质模型，该模型填充了储层属性，用于流体流动模拟，并通过动态注入数据进行全局校准。从1983年到2023年，深层注入的孔隙压力变化高达5 MPa，局部增加了原生孔隙压力状态的10%。模拟结果表明，发生在深层注入附近30公里范围内的地震经历了小幅度（<0.1 MPa）的孔隙压力增加，表明这些断层对有效应力变化高度敏感，并且比通常假定的0.6具有更低的摩擦稳定性。这些结果在理解美国最活跃、地质最复杂的盆地之一中诱发地震的应力变化方面起到了关键作用。

CMG软件应用情况：

在这项工作中，使用了CMG-STARS v.2019.10软件包来评估孔隙压力历史。流动模型有20层，从宾夕法尼亚系到前寒武纪基岩，受到地层解释的约束。模型的角点网格是270 × 220 km²，有123 × 116 × 20个单元格，大约是1.6 × 1.6 km²，并包括285,360个活跃单元格。平均单元格厚度是103米，85%的单元格厚度中位数范围从24到183米。网格单元在南北方向上对齐。流体属性如粘度和密度是作为温度、压力和盐度的函数计算的。

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Abstract

Rates of seismicity in the Delaware Basin of Texas and New Mexico increased from 10 earthquakes per year of local magnitude (ML) 3.0 and above in 2017 to more than 185 in 2022, coincident with increasing oil and gas production and wastewater re-injection into strata shallow or deeper than producing intervals. Events of large magnitude—up to ML 5.4 to-date—occur on faults extending into formations above the basement that have received more than four billion barrels of injection. Here, we demonstrate the link between injection geology, pore pressure evolution, fault stability, and induced seismicity in this region. We find that the injection targets are largely dolomitized platform carbonates with low (<5 vol.%) matrix porosity and fracture-enhanced permeability with inherent heterogeneity in flow properties. A comprehensive, three-dimensional geological model populated with reservoir properties is used for fluid flow modeling, with global calibration supplemented by dynamic injectivity data. Pore pressure changes with deep injection are up to 5 MPa from 1983 to 2023, increasing the native pore pressure state by 10% locally. Modeling results show that earthquakes occurring at distances of up to 30 km from deep injection have experienced small (<0.1 MPa) pore pressure increases, indicating that the faults hosting these earthquakes are highly sensitive to changes in effective stress and have lower frictional stability than the 0.6 generally assumed. These results serve as a critical step in understanding the stress changes that induce earthquakes in one of the most seismically active and geologically complex basins in the US.

Key Points

  • Injection of oil field wastewater into deep strata in the Delaware Basin causes pore pressure changes of up to 5 MPa
  • Earthquakes occurring in crystalline basement are likely induced by pore pressure diffusion associated with regional deep injection
  • Many basement-rooted faults hosting earthquakes are optimally oriented, sensitive, and slip with small pore pressure perturbations

作者单位：

德克萨斯大学奥斯汀分校

 

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