| 低温气体辅助煤层气压裂中的冷冲击机理 |
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| 引用本文： | 张亮,罗炯,崔国栋,范志坤,任韶然,张建光,杨勇,车航.低温气体辅助煤层气压裂中的冷冲击机理[J].地球科学,2016,41(4):664-674. |
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| 作者姓名： | 张亮 罗炯 崔国栋 范志坤 任韶然 张建光 杨勇 车航 |
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| 作者单位： | 1.中国石油大学石油工程学院，山东青岛 266580 |
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| 基金项目： | 国家科技重大专项项目(No.2009ZX05062-012-011);中石油2011校企合作研究基金项目(No.2011-HB-X308);中央高校基本科研业务费专项资金资助项目(Nos.13CX02052A,15CX05036A) |
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| 摘 要： | 液N2等气体辅助煤层气压裂的常规机理已较为清楚，但其低温特征对煤层物性的影响以及对压裂效果的改善机理尚未引起重视，缺乏理论认识.归纳总结了低温气体对煤岩的冷冲击作用机制，评价了地层水的结冰条件和低温气体的热物性，通过室内实验和数值模拟等手段验证和预测了液N2对煤岩及近井煤层的冷冲击效果，并进行了冷冲击机理应用潜力分析.研究结果表明，煤层气压裂过程中注入N2等低温气体对煤层进行冷冲击，可引起煤岩基质收缩和地层水结冰膨胀，使煤岩产生大量微裂缝和力学强度降低(10%~30%)，有利于实现冰晶暂堵和改善煤层气压裂效果.以沁水盆地樊庄区块3#煤层为例，当液N2注入总量为30~120 m3时，可在近井周围3~5 m内形成低温区(＜-20 ℃)，煤层孔隙度将平均增大约1.5倍，渗透率增大4倍，还可造成煤岩的拉伸和挤压破坏.利用低温气体的冷冲击机理及其产生的冰晶暂堵可以作为改进煤层气和页岩气压裂工艺的新方向.
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| 关 键 词： | 煤层气 液N2 CO2水合物 冷冲击 微裂缝 煤岩强度 煤矿 |
| 收稿时间： | 2015-05-06 |
Mechanisms of Cold Shock during Coalbed Fracturing Assisted with Cryogenic Gases |
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| Zhang Liang;Luo Jiong;Cui Guodong;Fan Zhikun;Ren Shaoran;Zhang Jianguang;Yang Yong;Che Hang.Mechanisms of Cold Shock during Coalbed Fracturing Assisted with Cryogenic Gases[J].Earth Science-Journal of China University of Geosciences,2016,41(4):664-674. |
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| Authors: | Zhang Liang;Luo Jiong;Cui Guodong;Fan Zhikun;Ren Shaoran;Zhang Jianguang;Yang Yong;Che Hang |
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| Affiliation: | Zhang Liang;Luo Jiong;Cui Guodong;Fan Zhikun;Ren Shaoran;Zhang Jianguang;Yang Yong;Che Hang;School of Petroleum Engineering,China University of Petroleum;Huabei Oilfield PetroChina; |
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| Abstract: | The common mechanisms of coalbed fracturing assisted with cryogenic gases, such as liquid nitrogen, have been relatively clear, but the impact of low-temperature characteristics of cryogenic gases on coalbed physical properties and its mechanism of improving the fracturing performance have not yet attracted wide attentions, and lack of theoretical understanding. The mechanisms of cold shock of cryogenic gases to the coal rock are summarized first. Then based on the freezing condition of formation water and the thermal properties of cryogenic gases, the cold shock performance of liquid nitrogen to the coal rock was verified by laboratory experiments, and the behavoirs of the cooled coalbed around the wellbore after liquid nitrogen injection were predicted by numerical simulation method. Then the application potential of cold shock was analyzed. The results show that injecting cryogenic gases, such as liquid nitrogen, during coalbed fracturing, can cause a cold shock to the coal rock around wellbore, which will induce the coal matrix shrinking and the formation water freezing. A large number of new microcracks will generate in the coal rock. The mechanical strength of the coal rock will decrease by 10%-30%. These phenomena are favorable for the ice temporary blocking and the improvement of coalbed fracturing. Taking the coalbed of layer 3 in the Fanzhuang block in the Qinshui basin as example, when a amount of liquid nitrogen with a volume of 30-120 m3 is injected underground, a good cooling and shock performance in the coalbed will be obtained within 3-5 m around wellbore. The porosity of the nearby coalbed will increase about 1.5 times and the permeability will increase 4 times. A stretching and squeezing damage may also occur in the coal rock around wellbore. The cold shock of cryogenic gases and its induced ice temporary blocking can be used for the improvement of hydraulic fracturing techniques in coalbed methane and shale gas wells. |
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