Title: Fracture characterisation of coal and its implication on coalbed methane development

Authors: Yong Li; Dazhen Tang; Hao Xu; Tonggang Chen

Addresses: College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China ' Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization, School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China ' Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization, School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China ' Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization, School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China

Abstract: Network of naturally occurring fractures provides an important parameter for fluid flow modelling and coalbed methane (CBM) production potential prediction. This paper presents a detailed study of coal fractures identified in coal samples recovered from five coal mines in Weibei Coalfield, China. Endogenetic fractures, including condensed fracture and static pressure fracture, and exogenetic fractures, including tensile, compression, shear and relaxation fracture, were found based on scanning electron microscopy (SEM). The heterogeneity of coal fractures reflected by X-ray computed tomography (CT) numbers was calculated, and the three-dimensional view shows that fractures resemble 'K' type. The nuclear magnetic resonance (NMR) test was conducted to understand the connectivity. Three types of transverse relaxation (T₂) time spectrum were classified, corresponding to micropores, mesopores and microfractures. The third spectrum P₃, representing microfractures in trimodal T₂ spectrum type disappeared after being centrifuged and indicated the significant role of fractures in coal permeability. Results, using the same source samples, show the fracture planar morphology and its origin by SEM, the stereoscopic shape by CT, and the fluid flow ability by NMR. [Received: July 8, 2014; Accepted: February 3, 2015]

Keywords: coalbed methane; scanning electron microscopy; SEM; X-ray CT; computed tomography; nuclear magnetic resonance; NMR; Ordos Basin; naturally occurring fractures; fluid flow modelling; microfractures; coal fractures; coal mines; China; endogenetic fractures; condensed fracture; static pressure fracture; exogenetic fractures; tensile fracture; compression fracture; shear fracture; relaxation fracture; mining industry.

DOI: 10.1504/IJOGCT.2016.077299

International Journal of Oil, Gas and Coal Technology, 2016 Vol.12 No.4, pp.396 - 411

Received: 27 Jul 2014
Accepted: 03 Feb 2015
Published online: 28 Jun 2016 *

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