| Summary: | This paper studies typical nonlinear models of fluid flow through multi-porous media in low-permeability reservoirs, analyzes hypothesis conditions, derivation process and the experimental data rationality, and clarifies some confusions in order to understand the fluid flow rules through multi-porous medium in low permeability reservoirs. There are three problems in establishing the models: first, hypothesis conditions cannot be proved, calculation values cannot be measured; second, wrong basic equation not only was used, but also wrong of derivation process, and derived equation is also a wrong equation; third, the threshold pressure gradients obtained from rock samples of low permeability reservoirs at the laboratory are too high, without rationality. The threshold pressure gradient does not exist in all of the low-permeability reservoirs, only when pressure coefficient of low-permeability reservoir is less than one, fluid flow through multi-porous media should need the threshold pressure gradient, threshold pressure gradient should not be considered in reservoir numerical simulation, productivity prediction and well testing in low permeability reservoirs development. To reveal flow rules of low permeability reservoirs and establish theory of low-permeability oilfield development it's necessary to develop the digital rock technology, innovate experimental skills of modern petrophysics and so on. Key words: low-permeability reservoir, non-Darcy flow, nonlinear flow, threshold pressure gradient, yield stress, non-Newtonian fluid, boundary layer effect
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