Int. J. of Oil, Gas and Coal Technology   »   2017 Vol.14, No.3

 

 

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.2017.10002920

 

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

 

Available online: 01 Feb 2017

 

 

Editors Full text accessAccess for SubscribersPurchase this articleComment on this article