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现行各类煤芯煤层气逸散量推算方法,均未考虑煤芯煤层气在不同钻井液环境下解吸过程的差异,可能导致煤层含气量测定结果出现偏差.为此,本文将钻井液条件下煤芯煤层气解吸视为一个变压解吸过程,以Langmuir方程和Fick第一定律为基础,综合考虑钻井液条件下影响煤层气解吸扩散的主要因素,通过物理模拟实验和理论探讨,建立了考虑游离气在内的钻井液条件下煤芯煤层气解吸-扩散模型及逸散量数值模拟求取方法.结果显示:数值模拟能够较为准确地拟合t-Qt物理模拟曲线,提钻过程最终解吸量数值模拟值和物理模拟值总体较为接近.通过对实测解吸数据求取逸散量发现,当逸散时间较长时,数值模拟结果普遍大于直接法计算结果.作者由此认为,采用中国目前方法推得的煤芯煤层气逸散量普遍偏低,有必要在深入研究基础上考虑对中国现行国家标准予以修订.
All the existing calculation methods of coal-bed methane emission are without considering the difference of desorption process of coal-bed methane in different drilling fluid environments, which may lead to deviation of gas content measurement results.Therefore, Based on the Langmuir equation and Fick’s first law, considering the main factors that affect the desorption and diffusion of coalbed methane under drilling fluid conditions, the coalbed methane desorption is considered as a process of pressure swing desorption. Based on the physical simulation experiments and theoretical discussions, Free gas, the desorption-diffusion model of coal-bed coalbed methane and the numerical simulation of escape amount under the conditions of drilling fluid including drilling fluid, the results show that the numerical simulation can fit t-Qt physical simulation curve more accurately, The numerical simulations are close to the physical ones.According to the measured desorption data, we can find the fugacity, when the fugitive time is longer, the numerical simulation results are generally larger than the direct method.The author thinks that using China’s current It is necessary to consider revising the existing national standards in China on the basis of in-depth research.