Conceptual Models for Correlation between Detrital Particles Contents and Pore Distribution of Shale: Taking the Silurian Longmaxi Formation in northwestern Guizhou as an example

Key words: 
• particle dispersed shale /
• laminated shale /
• micro pore /
• interparticle pore /
• porosity

Abstract: The composition, structure and particles arrangement of rocks determine the developmental characteristics of pores. However, there are few researches performed on the influence of detrital particles content and its arrangement patterns on the pore distribution of shale from the structural-genetic perspectives by far. The black shale of the Silurian Longmaxi Formation in northwestern Guizhou Province was taken as an example for the analysis of thin section, XRD and scanning electron microscopy (SEM), and two types of shales were divided as the "particle dispersal" and "lamellar" according to the arrangement patterns of detritus particles. The conceptual models of pore structure of shales were abstracted and the influence of detrital particles content on the pore development was analyzed. For the particle dispersed shale, the main type of pore is micro pores of clay minerals while the content of clastic particles is less than 52.4%, and the porosity decreases with increase of particles content. When the content of clastic particles reaches 52.4%, the porosity becomes the lowest and the interpartical pores are filled with clay. The interpartical pores will increase with the clastic particles content increasing, and the porosity will increase rapidly. For the laminar shale, the increase of grain content leads to the increase of intergranular pores and the increase of porosity in sand strip, and then result in the transformation of shale reservoir to conventional clastic reservoir gradually. These models can be helpful for a deepen understanding of the development mechanism of porosity in shale, tight sandstone and conventional sandstone, and also important implications to predict and evaluate unconventional reservoirs.