The complicated response mechanism of shale gas requires that a systematic pilot study
is conducted on the influences of resistivity log responses to help with subsequent
experimental design, physical derivations and resistivity simulations. The purpose
of this research is to clarify the main controlling factors of the resistivity log
responses and their semi-quantitative relationship in certain marine shale gas formations.
Comprehensive analyses on large core test datasets, including mineralogical, petrological,
geochemical and other data, from the Longmaxi-Wufeng Formation and the corresponding
resistivity logging curves are carried out in 4 shale gas areas. This research indicates
that in low-porosity systems, the mineral composition directly impacts the resistivity.
Carbonates with large intergranular pores and even intragranular pores increase the
resistivity. The hydrophilic nature of clay decreases the resistivity. When organic
matter is not carbonized, the organic matter and biosilica will further increase the
resistivity. Pyrite layers will cause a large drop in resistivity (to less than 5
omega m). The resistivity is lower where organic matter carbonization has occurred
in the studied reservoir. Mineral components, especially clay minerals and organic
matter, are the main controlling factors of the conductivity of low-porosity systems.
In addition, we propose that elemental logging can be used to characterize the comprehensive
effect of low-porosity s systems on the resistivity of the reservoir and can accurately
reflect the resistivity. These results will help to develop future studies on the
relationship between the electrical conductivity and saturation of shale gas rocks,
which is of great significance.