Abstract Coal failure has been observed in many coal seam reservoirs during gas production, which generated significant impacts to coal permeability and to the efficiency of gas recovery. In this paper we develop a flow-geomechanical-coupled numerical approach and use two genuine field examples to discuss the relevant large-scale coal failure behaviours in fields. One example is with the CBM production in Cedar Hill reservoir, San Juan Basin; and the other one is with the CO2-injected ECBM process in Allison Unit, San Juan Basin. Major observations from the present work include: 1) Laboratory tests and analytical analyses based on uniaxial strain conditions may have considerable deviations in prediction of the coal failure during gas production in fields, because such a condition would not hold there because of non-uniform pressure distributions in the field due to gas production/injection. 2) Field-scale coal strength parameters (e.g., the friction angle) should be remarkably weaker than its counterparts measured with core samples because, if otherwise, the coal failure that has been observed would not occur. 3) In CBM processes, coal failure usually occurs first in the immediate vicinity of a wellbore, and then may expand to the whole field with continuing gas depletion. 4) ECBM processes can have complex strain history including inelastic coal failure due to primary production as well as elastic unloading due to CO2 injection.

中文翻译：

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一次/强化采气过程中的煤层故障：油田故障如何发展

摘要 很多煤层储层在采气过程中都出现过失煤现象，对煤的渗透率和采气效率产生了显着影响。在本文中，我们开发了一种流动-地质力学耦合的数值方法，并使用两个真实的现场例子来讨论现场相关的大规模煤破坏行为。一个例子是圣胡安盆地雪松山水库的煤层气生产；另一个是在圣胡安盆地艾利森装置的注入二氧化碳的 ECBM 工艺。目前工作的主要观察结果包括：1）基于单轴应变条件的实验室测试和分析分析可能对田间采气过程中煤层破坏的预测存在相当大的偏差，因为由于气体生产/注入导致现场压力分布不均匀，因此这种情况不会在那里成立。2) 现场规模的煤强度参数（例如，摩擦角）应该明显弱于用岩心样品测量的对应物，因为否则，观察到的煤破坏将不会发生。3) 在煤层气过程中，煤层破坏通常首先发生在井眼附近，然后可能随着气体的持续枯竭而扩展到整个油田。4) ECBM 过程可能具有复杂的应变历史，包括由于初级生产导致的非弹性煤故障以及由于 CO2 注入导致的弹性卸载。摩擦角）应该比用岩心样品测量的对应物明显弱，因为否则，观察到的煤层失效就不会发生。3) 在煤层气过程中，煤层破坏通常首先发生在井眼附近，然后可能随着气体的持续枯竭而扩展到整个油田。4) ECBM 过程可能具有复杂的应变历史，包括由于初级生产导致的非弹性煤故障以及由于 CO2 注入导致的弹性卸载。摩擦角）应该比用岩心样品测量的对应物明显弱，因为否则，观察到的煤层失效就不会发生。3) 在煤层气过程中，煤层破坏通常首先发生在井眼附近，然后可能随着气体的持续枯竭而扩展到整个油田。4) ECBM 过程可能具有复杂的应变历史，包括由于初级生产导致的非弹性煤故障以及由于 CO2 注入导致的弹性卸载。