Abstract:

Based on the sedimentologic theory and acoustic transit mechanism and by using logging data of wells drilled with oil-based and water-based mud,this paper systematically analyzes features and control factors of various acoustic impedances and actual wave impedances met in sandstone-mudstone section while logging.Logging acoustic impedances of fluvial strata are largely influenced by drilling mud.Under the condition of using water-base mud,alteration of argillaceous strata and borehole collapse can often lead to mismatch or pseudomorph in inversion of logging acoustic impedance.In contrast,stratigraphic actual wave impedance is mainly controlled by shale contents,and it reaches its maximum value when the shale contents is equal to the stratigraphic maximum effective porosity.Generally,values of wave impedance in argillaceous sandstone and sandy mudstone are relatively large,while that in mudstone is relatively small,and that in sandstone is situated between the two.

Key words: interval transit time, rock density, wave impedance, shale content, log-constrained inversion