Effects of Microheterogeneous Wettability and Pore-Throat Structure on Asphaltene Precipitation in Tight Sandstone: Results from Nuclear Magnetic Resonance.

The pore throat structure and microheterogeneous wettability of tight sandstone reservoirs are complex, which leads to varying asphaltene precipitation locations, contents, and distributions in different pores during CO flooding. Clarifying the heterogeneous wettability of different pore throat structures and their effects on asphaltene precipitation and adsorption is crucial for improving CO displacement efficiency. A series of experiments were conducted in this study, including X-ray diffraction (XRD), cast thin section (CTS), field emission scanning electron microscopy (FE-SEM), high-pressure mercury intrusion (HPMI), environmental scanning electron microscopy (E-SEM), nuclear magnetic resonance (NMR), and CO flooding experiments, to investigate the pore structure complexity of tight sandstone reservoirs of the Yanchang Formation in the Ordos Basin, China.

Microscopic Mechanism of CO Displacement Oil in Different Pore Throat Radius Segments of Tight Sandstone Reservoirs.

The micropore structure of tight sandstone affects the efficiency of CO displacement of crude oil. As the pressure changes, the oil displacement efficiency ( ) in segments with different pore radii changes, and the asphaltene precipitation in the pores causes alterations in the pore structure and wettability, which constrain . Ten samples of tight sandstone from the Yanchang Formation in the Ordos Basin were selected for this study.