Nano- to Micron-Sized Pore Types and Pore Size Distribution in Fluvial, Lacustrine, Transitional and Marine Tight to Shale Oil and Gas Plays in China and US
Based on our recent core sample tests using scanning electron microscopy (SEM), focused ion beam-scanning electron microscopy (FIB-SEM), high-pressure mercury intrusion capillary porosimetry (MICP), gas adsorption e.g. CO2 and N2 and nuclear magnetic resonance (NMR) for tight carbonate, sandstone and shales deposited in fluvial, lacustrine, transitional and marine settings in U.S. and China, it is found that nano to micron-sized pores are dominant in the tight sand, tight carbonate to very tight shale reservoirs and FIB-SEM and gas adsorption methods can reveal the abundant nano-scale pores that the MICP could not render. Measurements combining FIB-SEM, gas adsorption, MICP and NMR are suggested to reveal the full range of pore and pore throat size distributions. The pores in tight/shale reservoirs can be classified into inorganic matrix related pores including interparticle and intraparticle pores, organic matter related pores (if organic matter is present) and inorganic fracture pores. The dominant pore types and distribution of nano to micron-scale pores and pore throats vary between tight and shale reservoirs. The combining measurements suggest the nano-pores dominate the pore systems of the marine and transitional shales, poorly-sorted and clay-rich tight sand in China and U.S.. The nano-pores are mainly contributed by inter-crystal pores, inorganic inter-crystal pores and organic pores (for organic-rich shale). The micron pores may dominate in clean tight sand reservoirs and bioclast-rich tight carbonates in U.S. and China. The tested lacustrine shale in Ordos Basin in China is dominated by micron-range pore throats contributed mainly by inorganic minerals.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017