Abstract Potential aquifer contamination has been a huge environmental concern for the implementation of underground coal gasification (UCG) as coal seams are frequently overlaid by an aquifer. To explore the general impact of cleats on the mass transfer problems in UCG, particularly in the vertical direction, a dual-permeability (DP) cleat model was integrated into a 3-D numerical model which is dimensionally extensive to account for the hydrostatic effect of an aquifer. It was found that cleats favour UCG production, and the prime operational parameter, i.e., the injection pressure, plays a dominant role in governing vertical mass transport in UCG. Syngas production retains some constancy with variable geological settings unless a surge in the injection pressure occurs. Higher pressure injection generates higher peak rates but delayed production. At near-hydrostatic injection, gas species attain a weak presence in the overburden contrary to expectations based on key geological parameters. However, gas saturation in the cap rock increases appreciably under above-hydrostatic injection. The role of higher injection pressure becomes so overwhelming that variations or heterogeneity in geological parameters produce little difference in the transfer problems.

中文翻译：

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割理对煤炭地下气化的一般水文地质影响

摘要 由于煤层经常被含水层覆盖，潜在的含水层污染一直是实施煤炭地下气化（UCG）的一个巨大的环境问题。为了探索割理对 UCG 中传质问题的一般影响，特别是在垂直方向上，双渗透性 (DP) 割理模型被整合到 3-D 数值模型中，该模型在维度上广泛考虑了流体静力效应一个含水层。发现割理有利于 UCG 生产，主要操作参数，即注入压力，在控制 UCG 的垂直质量传输中起主导作用。合成气生产在可变地质条件下保持一定的稳定性，除非注入压力发生激增。更高的压力注入会产生更高的峰值速率，但会延迟生产。在接近静水压注入时，与基于关键地质参数的预期相反，上覆岩层中的气体种类较弱。然而，在高于静水压注入的情况下，盖层中的气体饱和度显着增加。更高的注入压力的作用变得如此势不可挡，以至于地质参数的变化或异质性对传输问题几乎没有影响。