Research on the influences of different mineral compositions on the development of nanopores in shales

In order to characterize the pore structure and analyze the influences of different mineral components on the pore structure of shale,some chemical methods were used to remove carbonate,silicate and pyrite in the samples col- lected from fresh outcrop sections of Wufeng-Longmaxi Formation located at Shuanghe Town,Changning County in Si- chuan Basin. The nanopores structure of samples at the different stages of processing were measured by carbon dioxide and nitrogen adsorption and analyzed by isotherms and NLDFT method. The results show that for micropores,the re- moval of carbonate reduces the volume of micropores,while the removal of silicate and pyrite results in an increase of the volume of micropores. This phenomenon indicates the dissolved pores in carbonate provide some micropores for the shale. For the meso-macropores,the pore volume shows an increasing trend during the processes of removing the minerals,indicating the minor contribution of minerals for these types of pores. The proportional distributions of pores in different scales have no changes during the processes of removing minerals,showing a characteristic that the mesopores and micropores provide the pore volume and surface area,respectively. The pore size distribution of micropore has a more obvious influence by the mineral constituent than that of meso-macropore. The nanopores in the whole rock show the characteristic of pores in organic matter,the minerals in shale cover the original information of organic matter,es- pecially for the micropore,this is due to the minerals are in packed,fill or filled conditions with the organic matter. In summary,the organic matter is the most important factor in controlling the evolution of nanopores in shales.