Pore-Structure Characterization of the Eocene Sha-3 Sandstones in the Bohai Bay Basin, China

Abstract

Mercury Intrusion Capillary Pressure (MICP), Nuclear Magnetic Resonance (NMR), routine core analysis, thin sections, and scanning electron microscope (SEM) analysis were used to gain insight into the pore structure of the Eocene Sha-3 (the third member of Shahejie Formation) low permeability sandstones in Raoyang Sag, including pore type, pore geometry, pore size. Quantitative NMR parameters and petrophysical properties were integrated to build up the relationship between microscopic pore structure and macroscopic performance. The pore systems of Sha-3 sandstones are dominantly of residual intergranular pores, intragranular dissolution pores and intercrystallite micropores associated with authigenic clay minerals. The high threshold pressure and low mercury withdrawal efficiencies from MICP analysis indicate the poor pore connectivity and strong heterogeneous. Both uni- and bimodal T2 (transverse relaxation time) spectrum can be found because of the coexistence of small and large pores, and the T2 of majo...