APPLICATION OF NEUTRON SCATTERING TO QUANTIFY THE INFLUENCE OF WETTABILITY ON SHALE PORE CONNECTIVITY

Hydrocarbon transport in tight shale is greatly controlled by the pore connectivity between matrix pores and stimulated fracture network. The target of this study focuses on the organic-rich siliceous and calcareous shales from several typical shale plays with different thermal maturity and mineralogy. Pore structure (including porosity, pore size distribution, and pore accessibility) of the shales was characterized by using small angle neutron scattering (SANS) and ultra-SANS (USANS) techniques, as well as mercury injection capillary pressure (MICP) analyses. Owing to the capabilities of detecting inaccessible pore spaces not measurable by other fluid-invasion approaches, SANS/USANS can measure total porosity (i.e., connected and closed porosity) across nm-mm spectrum. Furthermore, contrast-matching experiments, using mixed deuterated/non-deuterated fluids (i.e., water and n-decane), were conducted on the same specimen to quantify the volume fraction of hydrophobic and hydrophilic pores. Results indicate that a significant contribution of pores at >100 nm diameter to the total porosity from (U)SANS, while MICP detects accessible porosity with predominant pore-throat size ranges in <50 nm. A combination of (U)SANS and MICP techniques gives a comprehensive picture of shale pore structure related to wettability.