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APPLIED GEOPHYSICS  2018, Vol. 15 Issue (2): 208-221    DOI: 10.1007/s11770-018-0685-6
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Conductivity model for pyrite-bearing laminated and dispersed shaly sands based on a differential equation and the generalized Archie equation
Guo Zhi-Hua1,2, Song Yan-Jie1,2, Tang Xiao-Min1,2, and Wang Chao1,3
1. College of Geo-science, Northeast Petroleum University, Heilongjiang Daqing 163318, China.
2. Accumulation and Development of Unconventional Oil and Gas, State Key Laboratory Cultivation Base jointly constructed by Heilongjiang Province and the Ministry of Science and Technology, Heilongjiang Daqing 163318, China.
3. No. 9 Oil Production Company Geological Team of Daqing Oilfield Company Ltd, Heilongjiang Daqing 163000, China.
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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 pyrite-bearing 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 satisfies 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.
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Key wordsPyrite   shale   sand   conductivity   Archie’s equation   differential equation     
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This work was supported by the National Natural Science Foundation of China (No. 41274110), and the Northeast Petroleum University Innovation Foundation for Postgraduate (No. YJSCX2016-003NEPU).

Cite this article:   
. Conductivity model for pyrite-bearing laminated and dispersed shaly sands based on a differential equation and the generalized Archie equation[J]. APPLIED GEOPHYSICS, 2018, 15(2): 208-221.
 
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