Experimental Study on Pore Structure and Mechanical Properties of Stratified Coal
Publication: International Journal of Geomechanics
Volume 17, Issue 12
Abstract
The most striking feature of liquid nitrogen (LN2) fracturing is to drastically reduce the temperature around the rock when LN2 is injected into the reservoir. The strong thermal gradient can significantly induce the internal thermal stress of the rock, which results in severe damage. In this study, the permeability, ultrasonic wave, and triaxial compression test were performed to investigate the influence of LN2 treatment on pore structure and mechanical properties of stratified coal. In the pore structure tests, the increasing range of permeability of LN2-treated samples is 100.3–149.6%, and the P-wave velocity decreases by 3.1–4.6%. In the triaxial compression tests, the compressive strength and elastic modulus of LN2-treated samples decrease by 11–39.6% and 18.2–32.1%, respectively. The experimental results indicate that LN2 treatment increases the connectivity of coal pores, improving its flow conductivity and permeability, which can effectively enhance the fracturing effect. Meanwhile, it also reduces the ability of coal to resist deformation and rupture, which contributes to the reduction of initiation pressure in the reservoir simulation. In addition, the analysis further suggests that the super low temperature thermal stress can greatly promote the generation of secondary cracks and the formation of complex fracture networks inside coal. The study provides an important reference for tight reservoir simulation of cryogenic fracturing.
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Acknowledgments
The authors would like to thank the National Natural Science Foundation of China (Grants. 51574270 and 51504280), the Changjiang Scholars and Innovative Research Team in University (Grant IRT_14R58), the Qingdao Science and Technology Project (Grant 15-9-1-55-jch), the Independent Innovation Research Project of Central University (Grant 16CX02022A), and the Talent Introduction Project of the China University of Petroleum (East China) (Grant YJ201601094) for their financial support.
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Published In
International Journal of Geomechanics
Volume 17 • Issue 12 • December 2017
Copyright
© 2017 American Society of Civil Engineers.
History
Received: Jan 6, 2017
Accepted: Jun 15, 2017
Published online: Sep 29, 2017
Published in print: Dec 1, 2017
Discussion open until: Mar 1, 2018
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