Effect of Pore Structure on Reservoir Quality and Oiliness in Paleogene Dongying Formation Sandstones in Nanpu Sag, Bohai Bay Basin, Eastern China

Abstract

Routine core analysis, thin sections under transited and ultraviolet light, scanning electron microscope (SEM) analysis, and nuclear magnetic resonance (NMR) measurements were used to investigate the pore structure of the Paleogene Dongying Formation sandstones in the Nanpu Sag, Bohai Bay Basin. Regression analysis was performed to build up the relationships between microscopic pore structures and macroscopic behaviors. The pore systems mainly include primary intergranular pores, intergranular and intragranular dissolution pores, and clay-dominated micropores. Most of the intergranular pore bodies are connected by effective necking and sheet like pore throats, while the intragranular pores and micropores are connected by bending-flake and narrow cluster pore throat. Unimodal, bimodal, or multimodal T2 (transverse relaxation time) distributions can be observed due to the wide ranges of pore bodies and throats in Dongying sandstones. Consequently, wide variations of NMR parameters are encountered, and high-...