Coal Macrolithotype Distribution and Its Genetic Analyses in the Deep Jiaozuo Coalfield Using Geophysical Logging...

Area of Science:

• Earth Science
• Geology
• Petroleum Geology

Background:

• Coal macrolithotype identification is vital for coalbed methane (CBM) exploration, influencing gas content and coal structure.
• Traditional core analysis for macrolithotype identification is costly, time-consuming, and challenging with broken cores.
• Geophysical logging offers a rapid and effective alternative for CBM well analysis.

Purpose of the Study:

• To establish geophysical logging response rules for different coal macrolithotypes.
• To analyze the relationship between coal macrolithotypes, coal facies, and pore structures.
• To assess the feasibility of using geophysical logging for CBM exploration targeting.

Main Methods:

• Quantitative analysis of logging cutoff numbers for various macrolithotypes from 75 coal cores.
• Establishment of response rules for natural gamma (GR), deep lateral resistivity (LLD), and gamma-gamma log (GGL) curves.
• Discussion of formation mechanisms based on coal facies and pore structure analysis.

Main Results:

• Distinct GR, LLD, and GGL responses were identified for different coal macrolithotypes, with GR and LLD increasing from bright to dull coal.
• Most macrolithotypes were distinguishable using established logging curve thresholds, though ash yield impacts accuracy.
• Vertical macrolithotype distribution in the Shanxi Formation reflects peat marsh environments, with variations in maceral content (vitrinite/inertinite).

Conclusions:

• Geophysical logging provides a rapid and effective method for coal macrolithotype identification in CBM wells.
• Accurate macrolithotype identification aids in determining CBM enrichment areas, well locations, and exploration horizons.
• While macrolithotype influences pore structure, it's not the sole determinant; ash content significantly affects logging identification validity.