Abstract: Abstract：According to the complex logging environment of sand-shale interbeded formation，the response of dual laterolog
to multilayered medium model in horizontal well has been analyzed by 3D finite element method. The numerical result shows
that the borehole diameter and mud resistivity，the thickness and resistivity of shoulder bed（mudstone）as well as the radius
of invasion and invasion zone resistivity make obvious influences on dual laterolog response. In the sand-shale formation，the
larger the borehole sizes and mud resistivity are，the more serious influence on Ra is. If mudstone’s resistivity is higher，the
apparent resistivity of dual laterolog changes more obviously. The shoulder bed which includes sandstone and mudstone makes
no impact on the apparent resistivity and the apparent resistivity curves of variation are nearly the same when bed thickness of
formation is beyond 8 meters. The lower the resistivity invasion is and the deeper it invades，the more the difference between
Ra and the real resistivity of formation is.

Key words: Key words：dual laterolog, horizontal well, interbeded sand-shale, multilayered model