Measurement of the surface diffusion coefficient for adsorbed gas in the fine mesopores and micropores of shale organic matter
Measurement of the surface diffusion coefficient for adsorbed gas in the fine mesopores and micropores of shale organic matter
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DOI：
10.1016/j.fuel.2016.05.069
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发表时间：
2016-10
期刊：
影响因子：
7.4
通讯作者：
Bin Yang;Yili Kang;Lijun You;Xiangchen Li;Qiang Chen
中科院分区：
文献类型：
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作者：
Bin Yang;Yili Kang;Lijun You;Xiangchen Li;Qiang Chen
在页岩储层中，地表扩散对吸附气的输运具有重要意义，其扩散系数的确定对储层评价和油田产量预测至关重要。提出了一种测量页岩岩心塞在原位条件下吸附气体（甲烷）表面扩散系数的压力衰减法。基于气体的储存和流动机制、孔径分布和物质平衡，排除了散输（非表面扩散）数据。用球形扩散模型对表征有机质细介孔和微孔表面扩散的数据进行了处理。与以往通过样品大小估算扩散距离的方法不同，本文采用简化几何模型和氧化处理后二氧化氮吸附测定的有机物BET表面积（4.08-9.52 m2/g）相结合的方法计算了扩散距离（114.5-190.4 nm）。测量得到的表面扩散系数约为10 ~ 16cm2/s，随气体压力的增大而增大，符合表面扩散理论。最终，虽然扩散系数较小，但考虑到扩散距离短、表面积大，表面扩散可以将吸附气输送到较大的流道中，促进页岩储层吸附气的产量。
In shale plays, the surface diffusion is of great significance in the mass transport of adsorbed gas, and obtaining its diffusion coefficient is crucial for reservoir evaluation as well as field production forecast. This paper presented a pressure decay method to measure the surface diffusion coefficient of adsorbed gas (methane) with shale core plugs under in-situ conditions. Based on the gas storage and flow mechanisms, pore size distribution and material balance, the bulk transport (non-surface diffusion) data was excluded. The data which represented the surface diffusion in the fine mesopores and micropores of organic matter was dealt with a spherical diffusion model. Unlike previous works which estimated the diffusion distance via sample size, the diffusing distance (114.5–190.4 nm) was calculated by combining a simplified geometric model and the BET surface area of the organic matter (4.08–9.52 m2/g) which was tested by N2-adsorption after oxidation treatments. The measured surface diffusion coefficient was about 10−16cm2/s, and increased with the growth of gas pressure, in accord with the surface diffusion theories. Ultimately, although the diffusion coefficient was small, considering the short diffusing distance and large surface area, surface diffusion could transport the adsorbed gas to big flow channels, promoting the output of adsorbed gas in shale reservoirs.