Contributions of pore-throat size distribution to reservoir quality and fluid distribution from NMR and MIP in tight sandy conglomerate reservoirs

Abstract

Overall pore-throat size distribution is a critical foundation for evaluating tight sandy conglomerate reservoirs. However, the pore-throat size cannot be easily obtained from a single technic due to the complex microstructure. In this paper, a new method was introduced to characterize the microstructure by combining thin sections, scanning electron microscopy (SEM), pressure-controlled injected mercury (PMI), rate-controlled injected mercury (RMI), and nuclear magnetic resonance (NMR). Twenty-four tight sandy conglomerate cores from the Baikouquan Formation of the Mabei oil field, northwest China, were selected to conduct the series of experiments. Overall pore-throat size distribution (TRD) was reconstructed by combining mercury injection porosimetry (MIP) with NMR with pores that were equivalent to triangular cross-section; the radii of the inscribed spheres were obtained to weaken the influence of irregular shapes by RMI. Irreducible water saturation of the cores was achieved by nitrogen displacement, which decreases with increasing of micropore proportion. An ideal relationship between permeability, movable water saturation, and micropore percentages was constructed which indicates the effect of microstructure on reservoir quality and fluid distribution in tight sandy conglomerate reservoirs.