TY - JOUR
T1 - Effect of coalification jumps on petrophysical properties of various metamorphic coals from different coalfields in China
AU - Zhou, Sandong
AU - Liu, Dameng
AU - Karpyn, Zuleima T.
AU - Cai, Yidong
AU - Yao, Yanbin
N1 - Funding Information:
This study was funded by the National Natural Science Foundation of China ( 41830427 ; 41772160 ; 41602170 ) and the Fundamental Research Funds for the Central Universities ( 2652017302 ). We also acknowledge the financial support from the China Scholarship Council (No. 201706400009 ). We also thank Prof. Zuleima T. Karpyn for contribution to the editing of the manuscript. The authors thank the editor and three anonymous reviewers for valuable remarks and insightful comments that led to improvements to our paper.
PY - 2018/12
Y1 - 2018/12
N2 - The effect of coalification jumps on petrophysical properties, and the evolution of porosity and permeability of metamorphic coals are poorly understood, which significantly influences coalbed methane extraction. We estimated pore throat diameter, specific surface area, connectivity, moveable fluid space, heterogeneity, porosity and permeability in a series of 41 coal samples (maximum reflectance of vitrinite in 0.34–4.24%) over six coalification jumps, by processing low temperature nitrogen adsorption, mercury intrusion porosimetry and nuclear magnetic resonance (NMR) measurements. Each coalification jump generally leads to abrupt change of petrophysical properties from dehydration to graphitization. Connectivity parameters (efficiency mercury withdrawal and the ratio of movable fluid to bounded fluid) and fractal dimensions (DNA1, DNA2, DMIP, DNMRS and DNMRM) present binomial function with vitrinite reflectance. Generations of thermogenic gas and fractures growth are attributed to increasing pore-fracture connectivity in bituminization and debituminization. Fractures begin healing and compaction, as well as reduced connectivity, at the fourth jump in graphitization. Heterogeneous pore-structures (high DMIP and DNMRM) usually have low connectivity. Moveable fluid space and its porosity from NMR are negatively correlated with the increase in coal rank. The evolution and origin of porosity and permeability (<1 mD) during coalification is proposed. Coal permeability (>1 mD) has no relation with coal rank and is related to fracture characteristics. Unlike the origin of porosity, which intrinsically inherits from progressive coalification, the origin of permeability is attributed to both progressive coalification and tectonic stresses. This study reveals the complex pore-fracture structures variation and the effect of stages in coal maturation on petrophysical properties of coalbed methane reservoirs.
AB - The effect of coalification jumps on petrophysical properties, and the evolution of porosity and permeability of metamorphic coals are poorly understood, which significantly influences coalbed methane extraction. We estimated pore throat diameter, specific surface area, connectivity, moveable fluid space, heterogeneity, porosity and permeability in a series of 41 coal samples (maximum reflectance of vitrinite in 0.34–4.24%) over six coalification jumps, by processing low temperature nitrogen adsorption, mercury intrusion porosimetry and nuclear magnetic resonance (NMR) measurements. Each coalification jump generally leads to abrupt change of petrophysical properties from dehydration to graphitization. Connectivity parameters (efficiency mercury withdrawal and the ratio of movable fluid to bounded fluid) and fractal dimensions (DNA1, DNA2, DMIP, DNMRS and DNMRM) present binomial function with vitrinite reflectance. Generations of thermogenic gas and fractures growth are attributed to increasing pore-fracture connectivity in bituminization and debituminization. Fractures begin healing and compaction, as well as reduced connectivity, at the fourth jump in graphitization. Heterogeneous pore-structures (high DMIP and DNMRM) usually have low connectivity. Moveable fluid space and its porosity from NMR are negatively correlated with the increase in coal rank. The evolution and origin of porosity and permeability (<1 mD) during coalification is proposed. Coal permeability (>1 mD) has no relation with coal rank and is related to fracture characteristics. Unlike the origin of porosity, which intrinsically inherits from progressive coalification, the origin of permeability is attributed to both progressive coalification and tectonic stresses. This study reveals the complex pore-fracture structures variation and the effect of stages in coal maturation on petrophysical properties of coalbed methane reservoirs.
UR - http://www.scopus.com/inward/record.url?scp=85055030404&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85055030404&partnerID=8YFLogxK
U2 - 10.1016/j.jngse.2018.10.004
DO - 10.1016/j.jngse.2018.10.004
M3 - Article
AN - SCOPUS:85055030404
SN - 1875-5100
VL - 60
SP - 63
EP - 76
JO - Journal of Natural Gas Science and Engineering
JF - Journal of Natural Gas Science and Engineering
ER -