Steam injection into oil sands reservoirs for bitumen extraction leads to the in situ generation of gases (mainly methane). Many oil sands formations have permeable cap rocks that may allow these gases to migrate to the overlying formations and pose environmental challenges to the groundwater. We present a detailed analysis of the long‐term fate of the in situ generated gases over the course of thermal oil recovery operations. The impacts of capillary barriers on upward migration of the in situ generated gases are quantified. Our findings reveal that the upward migration of gases over a 100‐year period in formations with continuous flow barriers with a permeability of less than ∼1 × 10⁻¹⁸ m² is negligible. However, for formations with discontinuous flow barriers, the migrated gas can potentially leak to the surface depending on the capillary entry pressure of the preferential pathways (e.g., sand layers). In this case, the upward migration is primarily controlled by high permeability pathways. It was found that the migrated gas is effectively trapped by the residual and dissolution trapping mechanisms, and the gas migration to the overlying formations is prevented or significantly reduced by capillary pressure of sand layers. The results indicate that the migrated gas to the shallow groundwater is primarily comprised of methane and is free of CO₂ and H₂S. These results provide valuable insights into the long‐term fate of these gases in thermal oil recovery operations. They also offer potential opportunities for the development of regulatory frameworks and screening considerations for caprock/seal integrity/risk assessments.

中文翻译：

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来自油砂热采作业的甲烷地下迁移

蒸汽注入油砂储层中用于沥青提取会导致就地产生气体（主要是甲烷）。许多油砂岩层都具有可渗透的盖层，可能使这些气体迁移到上覆岩层，并对地下水构成环境挑战。我们对热采油作业过程中原位生成气体的长期命运进行了详细分析。量化了毛细管屏障对原位产生的气体向上迁移的影响。我们的发现表明，在具有连续流动屏障且渗透率小于〜1×10 ^-18  m ^2的地层中，气体在100年内向上迁移可以忽略不计。但是，对于具有不连续导流壁的地层，根据优先通道（例如，沙层）的毛细管进入压力，迁移的气体可能会泄漏到地表。在这种情况下，向上迁移主要受高渗透率途径控制。已经发现，通过残留和溶解捕获机制有效地捕获了被迁移的气体，并且通过砂层的毛细压力阻止或显着减少了气体向上覆地层的迁移。结果表明，向浅层地下水迁移的天然气主要由甲烷组成，不含CO ₂和H _2。S.这些结果为热采油作业中这些气体的长期命运提供了宝贵的见解。它们也为监管框架的发展和筛查盖层/密封完整性/风险评估的考虑因素提供了潜在的机会。