Density logging is an effective method in the evaluation of coalbed methane (CBM) reservoirs. Whether densitylog values effectively represent true density of coal will directly determine precision of evaluating coalbed methaneparameter logs. In this paper, a statistical method is used to analyze density log response characteristics and hole enlargementrate for three main coal beds in the study area in order to determine the internal relation between hole enlargementrate and density response. Analytical results show that distortion of density log response values is caused mainly by holeenlargement impacts. Based on the apparent geometric factor theory, a model suitable for correcting hole enlargement impactsdensity logs for coalbed methane reservoirs has been deduced. To correct density logs for hole enlargement influences,it is key to determine a mud apparent geometric factor. Using measured apparent relative density, density log valuesand caliper logs for coal rock, the least squares fitting method was adopted to obtain computation model constants forthe mud apparent geometric factor applicable to the study area. When this model was applied in a computer autocorrectingprocess for evaluating enlargement impacts on density logs for coalbed methane reservoirs of the Hancheng gasfield in the eastern section of Ordos Basin, China, the correction results were very close to measured relative density, indicatingthat this method can improve precision of correcting hole enlargement impacts on density logs.
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