Отправлено: 10.03.19 07:15. Заголовок: Conductivity model for pyrite-bearing laminated and dispersed shaly sands based on a differential eq

Conductivity model for pyrite-bearing laminated and dispersed shaly sands based on a differential equation and the generalized Archie equation*
APPLIED GEOPHYSICS, Vol.15, No.2 (June 2018), P. 208–221, 18 Figures.

Guo Zhi-Hua1,2, Song Yan-Jie♦1,2, Tang Xiao-Min1,2, and Wang Chao1

Abstract: The conductance of pyrite-bearing laminated and dispersed shaly sands is not
well understood and resistivity models for pyrite-bearing shaly sands are nonexistent.
Thus, we first synthesize clean pyrite-matrix samples, and quartz-matrix samples with
variable laminated shale, dispersed shale, and pyrite content and then perform petrophysics
experiments to assess the effect of pyrite content on the conductivity of pyrite-bearing
shaly sands. Second, based on the differences in conductivity and conduction pathways and
geometries because of the variable composition of the pyrite-bearing laminated and dispersed
shaly sands, we divide the shaly sands into their components, i.e., laminated shale, quartz
grains, pyrite grains, hydrocarbon, dispersed shale, microscopic capillary water, and mobile
water.

A generalized resistivity model is proposed to describe the conductivity of pyritebearing laminated and dispersed shaly sands,
based on the combined conductivity differential equation and generalized Archie equation.

In the generalized resistivity model, the conductivity differential equation is used to describe
the conductivity of dispersed inclusions in a host, whereas the generalized Archie equation is used to describe the conductivity
of two conducting phases.

Moreover, parallel conductance theory is used to describe the conductivity of dispersed shaly sands and laminated shale.

Theoretical analysis suggests that the proposed model satisfi es the physical constraints and the model and experimental
results agree. The resistivity and resistivity index of shaly sands decrease with increasing
conductivity and pyrite.

Finally, the accuracy of the resistivity model is assessed based on
experimental data from 46 synthetic core samples with different oil saturation.

The model can describe the conductivity of clean pyrite-matrix samples, and quartz-matrix samples
with different volumes of laminated shale, dispersed shale, and pyrite. An accurate saturation
model of pyrite-bearing laminated and dispersed shaly sands is thus obtained and the log data
interpretation in complex shaly sands can improve with the proposed model.