河流相地层波阻抗特征及其控制因素

利用油、水基泥浆测井资料,根据沉积学原理、声波传播机理系统分析了砂泥岩剖面各类岩性测井声阻抗、真实波阻抗变化特征及其控制因素。河流相地层测井声阻抗受钻井泥浆的影响较大,在水基泥浆条件下,由于含泥质地层的蚀变以及井眼跨塌,往往导致测井波阻抗反演时的不匹配或假象。地层真实的波阻抗则主要受泥质含量控制。当泥质含量等于该套地层的最大有效孔隙度时,其波阻抗值最大。一般而言,泥质砂岩、砂质泥岩的波阻抗值较大,泥岩波阻抗值较小,而砂岩介于两者之间。

Features and control factors of wave impedance of fluvial strata

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.