Abstract
In this paper, two novel methods to correct the effect of ash on logs are firstly introduced. The corrected log responses of density in coal bed are in accordance with the changing rule of density of laboratory. The hydrogen index of coals with different ranks is simulated. And the simulated neutrons are well verified by logs. After obtaining the accurate variation of density and neutron along with coalification, the log response behaviors of density and neutron in coal bed with different ranks are analyzed and discussed in detail. The values of bulk density and neutron porosity for higher rank ash-free coals are also proposed, which make supplement for the petrophysical knowledge base. Finally, a cross plot of density versus neutron logs is proposed to identify coal ranks, and it has been successfully applied to various CBM fields of several basins in China.
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