Hydrodynamic mechanism of interlayer interference and dynamic commingled production limits in low-permeability heterogeneous porous media: The role of threshold pressure gradient

In the commingled production of low-permeability heterogeneous porous media, the non-Darcy flow characteristics governed by the threshold pressure gradient (TPG) induce complex interlayer interference, significantly compromising fluid mobilization. By integrating a TPG-based nonlinear flow model with physical simulation experiments, the quantitative mechanism of hydrodynamic shunting is elucidated, and the dynamic limits of commingled production are determined. The results demonstrate that interlayer interference is inherent to commingled systems and significantly intensifies with increasing heterogeneity, leading to a marked increase in productivity deficit as the permeability ratio widens. Although rising water cut reduces fluid viscosity and flow resistance, the intensified shunting effect in high-permeability layers causes the effective pressure coefficient (β) of low-permeability layers to decay at a rate significantly outpacing the resistance reduction. Flow stagnation occurs once the effective driving force fails to overcome the TPG barrier (β G/▽Psys). This mechanism is corroborated by nuclear magnetic resonance imaging, which visualizes the spatial evolution of residual oil from uniform displacement to central enrichment, and finally to a completely unswept dead-oil state. Furthermore, a dynamic limit chart for commingled production is established, revealing a distinct time-dependent contraction of the feasible domain. Governed by the coupling of fluid rheology and shunting intensity, the maximum allowable permeability ratio decreases significantly from the early to late water-cut stages. These findings highlight the progressive inadequacy of static layer subdivision schemes and necessitate the implementation of dynamic layer reorganization to mitigate the intensified interlayer interference caused by expanding hydrodynamic disparities.