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Description
Multi-phase fluid transport in the subsurface natural porous sandstone governs numerous energetic, industrial, and environment activities. A new approach for nanometer-millimeter pore connectivity quantification is compiled by integration of multiple scale pore structure characterization techniques involving casting thin section (CTS), scanning electron microscope (SEM), X-ray tomography (X-μCT), Nuclear magnetic resonance (NMR), pressure-controlled porosimetry (PCP), and rate-controlled porosimetry (RCP), whereby the pore connected pattern, pore connective ratio, and connected full-range pore size distribution (CPSD) are obtained by determining the full-range pore size distribution (FPSD) and empirical correlations between pore size and connective ratio, whereas the reason for the steady-state two-phase flow (STPF) physics are further explored by combined physical simulation of steady-state two-phase fluid flow experiment. Connectivity evaluation indicates that high permeable sandstone shares a reticular connection network with scale-invariant connected ratio stays at around 0.60, low-permeability sandstone exhibits branch-like pattern with the ratio ranging from 0.53 to 0.60, while tight sandstone is characterized by local chain-like pattern with an average ratio of 0.31. A connectivity prediction model,lgC=0.0526lgK+0.0229φ+0.0004Rc50-0.6391, for all types of sandstone is built.With decreasing connectivity ratio, deviated Darcy linear and power-law flows present successively in the fractional non-wetting phase flow in STPF, which can be described as v=α(dP⁄dL-dP0⁄dL0 ) and v=b(dP⁄dL-dP0⁄dL0)^c, respectively. Wetting phase mobility, dynamics of multi-phase interaction, dynamic variation of non-wetting phase flow path are interpreted based on the connected full-range pore size distribution (CPSD), incorporating DLVO theory, augmented Young-Laplace equation, and effective hydraulic radius model, give good explanations for the flow physics. It indicates that the CPSD determines multi-phase fluid mobility potential and dynamics between multi-phase interaction, which control the expansion pattern of non-wetting phase pathway. Preferential non-wetting phase flow path expansions in the outer layer and inner layer of bound water film and accompanying induced flow resistances in the connected pores < 1000 nm primarily control the flow regime distinctions in linear and power-law flows. The pores of 30-50 nm in the flow paths are responsible for threshold pressure gradient (TPG), pressure disorders, and snap-offs during non-wetting phase flow, responsible for power-law flow deviations. A dynamic fractional non-wetting phase flux prediction model is proposed by modifying fractal-based Hagen-Poiseuille equation considering flow physics, pore heterogeneity, and critical percolation length scale along with flow path expansions.
| References | Armstrong RT, McClure JE, Berrill MA, Rücker M, Schlüter S, Berg S., 2016.Beyond Darcy's law: The role of phase topology and ganglion dynamics for two-fluid flow. Phys. Rev. E, 94(4):043113. |
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| Country | China |
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