Title: Hydraulic fracturing mechanisms in coal: a review

Authors: Josef Blunschi; John Wang; Turgay Ertekin

Addresses: Petroleum and Natural Gas Engineering, The Pennsylvania State University, 230 Hosler Building, University Park, PA 16802, USA ' Petroleum and Natural Gas Engineering, The Pennsylvania State University, 202 Hosler Building, University Park, PA 16802, USA ' Petroleum and Natural Gas Engineering, The Pennsylvania State University, 118 Hosler Building, University Park, PA 16802, USA

Abstract: Hydraulic fracturing mechanisms in coal differ in many aspects from those in inorganic rocks. Due to the lower Young's modulus and higher Poisson's ratio, the stress state in coal is higher than in adjacent formations. This leads to wider and shorter fractures than in inorganic rocks. Fractures are affected by the cleat system in coal, so that multiple fractures may follow in tortuous paths the coal cleats. Coal often has a fracture treatment pressure in excess of 22.6 kPa/m (1 psi/ft.). Several hydraulic fracturing mechanisms may account for that, namely fracture blocking by coal chips, fracture tip plugging by coal or the development of a complex multi fracture system. The orientation of the hydraulic fractures is predominantly horizontal at shallow depths (< 200 m) and mostly vertical at depths > 600 m. In between these depths, fracture orientation may be either horizontal or vertical. This paper gives a comprehensive overview of the proposed hydraulic fracturing mechanisms in coal. [Received: July 28, 2015; Accepted: January 14, 2016]

Keywords: coal bed methane; CBM; hydraulic fracturing; fracking; coal cleats; fracture tip plugging; parallel fractures; coal fines; review; fracture blocking; coal chips; fracture orientation.

DOI: 10.1504/IJOGCT.2017.082050

International Journal of Oil, Gas and Coal Technology, 2017 Vol.14 No.3, pp.247 - 263

Received: 30 Jul 2015
Accepted: 14 Jan 2016
Published online: 06 Feb 2017 *

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