InterPore2026

Fluid Occurrence Mechanisms in Deep Tight Sandstones: Quantitative Characterization of Pore Structure and Effective Pore-Throat Cutoffs via Integrated Experiments

19 May 2026, 09:50

1h 30m

Poster Presentation (MS13) Fluids in Nanoporous Media Poster

Speaker

Sha Li

Description

Tight sandstone reservoirs, representing a substantial fraction of global unconventional hydrocarbon resources, are characterized by complex pore structures and high heterogeneity, which pose significant challenges to resource evaluation and efficient development. Water saturation (Sw) serves as a critical physical parameter for revealing the evolution laws of multiphase fluids in porous media, characterizing fluid migration efficiency, and evaluating fluid mobility. However, due to the high heterogeneity of pore structures in tight formations, analyses based solely on single reservoir parameters fail to accurately depict fluid distribution and migration mechanisms.

Consequently, this study adopts a synergistic research methodology combining multi-scale characterization, multi-gradient fluid injection, and multi-method experimental integration to systematically explore reservoir internal fluid distribution and transport mechanisms. First, utilizing multi-scale characterization techniques—including Scanning Electron Microscopy (SEM), High-Pressure Mercury Injection (HPMI), Nuclear Magnetic Resonance (NMR), Micro-CT imaging, and Digital Core Simulation—we systematically characterized the pore structure features from micro to meso scales, clarifying the spatial morphology and pore-throat configurations of the porous media. Second, by integrating Gas-Driven Dynamic Injection Experiments (GDDIE) with NMR technology, fluid injection was conducted under varying charging pressures and confining pressures to precisely characterize the distribution features of different fluids. Assisted by large-field SEM stitching and Micro-CT imaging, the fluid distribution in samples post-displacement was visually characterized across scales, revealing fluid occurrence states in tight reservoirs. Finally, synthesizing results from dynamic injection, HPMI, NMR, and digital core simulations, the internal fluid migration mechanisms were deeply dissected. . A novel method was developed to quantify movable fluid within specific pore‑size intervals by constraining NMR‑derived pore‑size distributions with gravimetrically measured movable‑fluid mass, thereby experimentally determining the actual pore‑size cutoff between movable and bound fluid and validating theoretical NMR T₂ cutoffs.

Key findings reveal that Sw distribution is governed by the coupling of pore geometry (size, connectivity) and surface properties (mineralogy, wettability). Specifically, low‑water‑saturation reservoirs, dominated by primary pores with "large‑pore/coarse‑throat/strong‑connectivity" (pore‑throat ratio <5, coordination number >3), can effectively displace 15% of total movable fluid in nanopores under low pressure (<2 MPa), achieving a maximum relative movable fluid saturation of 81.2%. Medium‑water‑saturation reservoirs, primarily composed of dissolution pores with "large‑pore/fine‑throat/weak‑connectivity", require higher pressure (~4 MPa) to mobilize nanopore fluid and exhibit a maximum relative movable fluid saturation of 47.03%. In contrast, high‑water‑saturation reservoirs are nanopore‑dominated with poor connectivity; only under high pressure (>10 MPa) can a small amount of fluid be mobilized, yielding a maximum relative movable fluid saturation of merely 28.12%. Displacement threshold pressure is lowest in large‑pore‑coarse‑throat systems, with movable water in sub‑micron pores displaced first, and flow from 10–100 nm pores initiating above 4 MPa before stabilizing.

This study provides a critical quantitative basis for the precise assessment of reservoir fluid content from a micro-mechanism perspective.