Lithofacies heterogeneity and reservoir pore development characteristics of continental shale: A case study of the Dongyuemiao shale of the Ziliujing Formation in the Sichuan Basin

Abstract

Objective After the exploration break through of the Well Fuye 10 in the Fuxing area of the Sichuan Basin, shale oil and gas from the Dongyuemiao section of the Jurassic Ziliujing Formation showed good exploration potential. The Dongyuemiao shale is characterized by unique shell limestone interlayers, high clay mineral content (up to 60%), various reservoir pore types, and strong vertical heterogeneity. Methods Taking the Well Xingye X as an example, combined with logging data, core observation, argon ion polishing scanning electron microscopy (SPE), and other technical means, the lithofacies characteristics and pore development characteristics of continental shale in the Dongyuemiao section were emphatically analysed. Results In this study, the principle of continental shale lithofacies division of "interlayer+mineral three-terminalelements" was established, and the continental shale of the Dongyuemiao section was vertically divided into 6 lithofacies: shell rhythmic mixed shale facies, silt shell interbedded clay shale facies, silt lithic interbedded mixed shale facies, lithic limestone facies, lithic interbedded mixed shale facies, and lithic interbedded clay shale facies. Through argon ion polishing and scanning electron microscopy (SEM), it was found that this set of continental shale mainly develops special complex organic clay pores, of which the lithic interbedded clay shale facies was the most developed type of organic pore, while the lithic limestone facies organic pores were not developed, mainly develop intragranular dissolved pores. The mercury intrusion nitrogen adsorption joint measurement results revealed that there was no significant difference in the pore size distribution of the six lithofacies shales. Conclusion Comprehensive analysis revealed that the interaction between organic matter and clay minerals during the diagenetic evolution process was the main factor influencing the pore development of continental shale in the Dongyuemiao section.

Keywords

• continental shale
• lithofacies heterogeneity
• organic-clay complex pore
• jurassic
• dongyuemiao section
• sichuan basin