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Energies 2017, 10(5), 654; doi:10.3390/en10050654

Study on the Propagation Laws of Hydrofractures Meeting a Faulted Structure in the Coal Seam

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1,2,* , 1,2
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1,2
and
3
1
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
2
National & Local Joint Engineering Laboratory of Gas Drainage in Complex Coal Seam, Chongqing University, Chongqing 400044, China
3
China Coal Technology Engineering Group Chongqing Research Institute, Chongqing 400037, China
*
Author to whom correspondence should be addressed.
Academic Editor: Mehrdad Massoudi
Received: 21 February 2017 / Revised: 2 April 2017 / Accepted: 5 May 2017 / Published: 10 May 2017
(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)
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Abstract

Hydraulic fracturing is an important technique for increasing coal seam permeability and productivity of CBM (coalbed methane). As a common type of faulted structure in the coal seam, the fault has a direct impact on the direction and scope of hydrofracture propagation, weakening fracturing effects. To study the propagation laws of a hydrofracture meeting a fault in the coal seam, based on a two-dimensional model of a hydrofracture meeting a fault, the combined elastic mechanics and fracture mechanics, the propagation mode, critical internal water pressure, and influencing factors were analyzed. A numerical simulation on the propagation laws of hydrofracture meeting a fault was conducted by using the coupling system of flow and solid in the rock failure process analysis (RFPA2D-Flow). The results show that the horizontal crustal stress difference, the intersection angle between hydrofracture and fault plane, and the physical mechanics characteristics of coal-rock bed are the main factors influencing fracture propagation. With a decrease of horizontal crustal stress differences, intersection angle and an increase of roof elasticity modulus, it is easier for the footwall hydrofracture to enter the hanging wall along the bedding plane, forming an effective fracture. When the stress difference is large and the dip angle of fault plane surpasses 45°, the hydrofracture is easy to propagate towards the coal roof and floor by going through the fault plane. At this time, the coal seams of the footwall and the hanging wall should be fractured respectively to ensure fracturing effects, and the support of the roof and floor should be strengthened. The field experiment, theoretical analysis and numerical simulation were consistent in their results, which will contribute to the optimization of hydraulic fracturing and the prediction of hydrofracture in the coal seams containing faults. View Full-Text
Keywords: coal seam; faulted structure; hydraulic fracturing; hydrofracture propagation coal seam; faulted structure; hydraulic fracturing; hydrofracture propagation
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Wang, H.; Xia, B.; Lu, Y.; Gong, T.; Zhang, R. Study on the Propagation Laws of Hydrofractures Meeting a Faulted Structure in the Coal Seam. Energies 2017, 10, 654.

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