Methane cracking within shale rocks: A new explanation for carbon isotope reversal of shale gas
Methane cracking within shale rocks: A new explanation for carbon isotope reversal of shale gas
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页岩内的甲烷裂解：页岩气碳同位素逆转的新解释
DOI：
10.1016/j.marpetgeo.2020.104591
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发表时间：
2020-11
影响因子：
4.2
通讯作者：
Ping'an Peng
中科院分区：
文献类型：
--
作者：
Bin Cheng;Jianbing Xu;Qian Deng;Zewen Liao;Yunpeng Wang;Oluwabamise Lekan Faboya;Shida Li;Jinzhong Liu;Ping'an Peng
碳同位素反转（δ 13 Cmethane> δ 13 Cethane）的页岩气，作为一种有希望的资源“甜点”指示剂，往往产于高干度（Cmethane/（Cmethane+ Cethane）> 0.97）的高-过成熟页岩中。然而，这种逆转的原因仍然存在争议，仍然是一个悬而未决的问题。在本工作中，我们提出高过成熟页岩中的甲烷裂解作为解释这种逆转的可能机制之一，这将进一步加深对页岩气碳同位素逆转的认识。为了验证这一假设，在封闭的金管体系中进行了页岩气甲烷热解实验，以探讨页岩气碳同位素反转的发生机制。从热解产物中，检测到CH 4的裂解和C2 H4，C2 H6和C3 H8等更高数烃的产生。CH 4裂解生成C2 H6导致残余CH 4富集13 C，而生成的C2 H6贫化13 C。根据我们的实验结果和来自世界不同地区的583个页岩气藏样品的数据分析，我们认为CH 4在高-过成熟页岩中裂解并结合成C2 H6。当甲烷衍生C2 H6的贡献足够大时，通常发现的δ 13 C甲烷< δ 13 C乙烷的顺序将随着成熟度的增加而改变（例如镜质体反射率，Ro > ~2.0%），页岩气的碳同位素将发生逆转。以美国沃斯堡盆地的巴内特页岩为应用代表的页岩气藏，其演化范围涵盖了δ 13 Cethane随δ 13 Cethane的增加而增加，随后减少，从而开始碳同位素反转的过程。
Shale gas with carbon isotope reversal (δ13Cmethane> δ13Cethane), as a promising indicator for resource “sweet-spot”, tends to occur at high-over maturity shales with high gas dryness index (Cmethane/(Cmethane+ Cethane) > 0.97). However, the cause for this reversal is still controversial and remains an open question. In the present work, we propose methane cracking within high-over matured shale rocks, as one of the possible mechanisms, to explain this reversal, which will further enhance the knowledge about carbon isotope reversal of shale gas. In order to validate this hypothesis, methane pyrolysis experiments were carried out in closed gold-tube system to investigate the mechanism of occurrence of carbon isotope reversal in shale gas. From the pyrolysates, the cracking of CH4and the generation of higher number hydrocarbons like C2H4, C2H6,and C3H8were detected. The CH4cracking and the subsequent formation of C2H6led to the residual CH4being enriched in13C whereas the produced C2H6is depleted in13C. Based on our experimental results and the data analysis of 583 samples from shale gas reservoirs from different regions of the world, we suggest that CH4will be cracked and combined into C2H6in high-over matured shales. When the contribution from methane-derived C2H6is sufficiently massive, the commonly found order of δ13Cmethane< δ13Cethanewill change with increasing maturity (e.g. vitrinite reflectance,Ro > ~2.0%) and a carbon isotope reversal will occur for the shale gas. The Barnett shale from Fort Worth Basin, USA, as the application representative shale gas reservoir, cover the evolution scope of the increase and subsequent decrease of δ13Cethanealong with increase of δ13Cmethaneand thus the beginning of the carbon isotope reversal.
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影响因子：
1.8
作者：
Zhong Ningning
通讯作者：
Zhong Ningning
影响因子：
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作者：
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影响因子：
5.6
作者：
Rui Yang;Sheng He;Q. Hu;Dongfeng Hu;Jizheng Yi
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影响因子：
3.4
作者：
Cheng Bin;Liang Yungan;Xu Jianbing;Deng Qian;Wei Zhiwei;Faboya Oluwabamise L.;Liao Zewen
通讯作者：
Liao Zewen
影响因子：
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作者：
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通讯作者：
A. Milkov;M. Faiz;G. Etiope