It has been shown that high contents of organic matters in gas shales can provide excellent original organic richness and high generation potential, resulting in higher gas-in-place volumes. Nanopores in the organic matters are believed to be the predominant pore type in the Barnett mudstones generated during thermal maturation. It is therefore important to understand the evolution of pores in organic matters during the process of thermal maturation in order to quantitatively predict the storage space in gas shales. The evolution of pores in organic-rich shales during thermal maturation was investigated. An alloy reactor was used to perform pyrolysis experiments on an immature shale collected from the Fushun Basin, northeast China. Residues of different maturation were obtained for pore characterization and various measurements including gas compositions and yields, fluorescence characteristics and vitrinite reflectance for cross calibration. Nano-pores in the shale residues were measured using Small Angle X-ray Scattering (SAXS), Scanning Electron Microscope(SEM) and N2 gas adsorption at low temperature and pressure. Also, nanopore developed in natural samples of different thermal maturity was observed for comparison. It has been found that with increasing thermal maturity (i.e. pyrolysis temperature), the pores in the shale become more abundant. From 300 C to 600 C, the pore sizes increase by up to 35%, while the pore volumes increase by 10.2 cc/kg. The threshold temperature for such a change is around 400-450 C, equivalent to a vitrinite reflectance (Ro%) value of 1.0-1.8%, which also corresponds to the maximum oil generation as indicated by fluorescence intensity and a moderate gas yield. It is believed that the increase of nano-scale pore sizes and the total volumes is directly related to hydrocarbon generation process during the shale maturation process. The experimental findings are consistent with the porosity changing ranges for shales with varying maturities directly measured from the Ordovician Collingwood shale in USA, covering a maturity range from immature to over-mature with Ro value ranging from 0.70% to 1.62%, and gas shales from the Sichuan Basin, China, with Ro values greater than 2.0% and bulk He porosities of 0.47% - 2.40%.
AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016