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The production splitting coefficient is a key parameter for predicting gas production and reserves, evaluating gas recovery efficiency, and guiding the optimization of well patterns in multilayer commingled gas reservoirs. Therefore, developing a reliable splitting method to calculate this coefficient is critical for the development of multilayered commingled gas reservoirs. The gas drainage radius emerges as a key parameter in determining the production splitting coefficient grounded in the physical concept of production splitting. This coefficient is influenced by several factors—such as the wellbore radius, production layer thickness, porosity, initial gas saturation, gas deviation coefficient, reservoir temperature, gas drainage radius, and average formation pressure. Usually, calculating the gas drainage radius and average formation pressure cannot be performed in actual applications. Combining the gas well deliverability and material balance equations forms a closed-loop model for calculating the production splitting coefficient. This model features three equations with three unknowns—gas drainage radius, average formation pressure, and the production splitting coefficient. It introduces a double-cycle calculation method to solve the model. Specifically, the internal cycle computes the gas drainage radius, whereas the external cycle determines the production splitting coefficient, each offering unique solutions and employing alternating forward recursion and reverse recursion rules. The establishment of a double-cycle calculation process—defined by specific cycle step sizes and an error threshold—ensures that the external cycle progresses only upon the convergence of the internal cycle. Moreover, it determines whether the internal cycle can converge. Numerical simulations demonstrate that the production splitting coefficient exhibits different patterns across different production stage layers, highlighting the accuracy and mechanism soundness of the double-cycle method compared with direct numerical simulations. Moreover, it has good feasibility in field application because it can calculate the production splitting coefficient even without known values for gas drainage radius. Comparing gas-producing profiles indicates that the dual-cycle calculation method has reliable accuracy in field applications when the gas drainage radius and average formation pressure are unknown. Ultimately, the double-cycle calculation method offers a comprehensive solution for a three-element equation system, enabling simultaneous estimations of the production splitting coefficient, gas drainage radius, and average formation pressure.

The oil-water imbibition equation in the nano-scale pores considering the dynamic contact angle effect, nanoconfinement effect, inertia effect, and inlet end effect was established, and the relation between the friction coefficient of solid-oil-water three-phase contact line and the fluid viscosity in the interface zone was derived. In combination with the capillary bundle model and the lognormal distribution theory, the imbibition model of tight core was obtained and key parameters affecting imbibition dynamics were analyzed. The study shows that in the process of nanopore imbibition, the dynamic contact angle effect has the most significant impact on the imbibition, followed by nanoconfinement effect (multilayer sticking effect and slippage effect), and the inertia effect and inlet end effect have the least impact; in the initial stage of imbibition, the effect of inertial force decreases, and the effect of contact line friction increases, so the dynamic contact angle gradually increases from the initial equilibrium contact angle to the maximum and then remains basically stable; in the later stage of imbibition, the effect of contact line friction decreases, and the contact angle gradually decreases from the maximum dynamic contact angle and approaches the initial equilibrium contact angle; as the pore radius decreases, the dynamic contact angle effect increases in the initial stage of imbibition and decreases in the later stage of imbibition; as the oil-water interfacial tension increases, the imbibition power increases, and the dynamic contact angle effect increases; there is a critical value for the influence of interfacial tension on the imbibition dynamics. In improving oil recovery by imbibition in tight oil reservoir, interfacial tension too low cannot achieve good imbibition effect, and the best interfacial tension needs to be obtained through optimization.

To quantitatively evaluate the impact of non-equilibrium phase transition on degassing in an oil-gas system and accurately determine the bubble point pressure of the system with different oil rates, a model, which takes the influence of pressure drop and non-equilibrium phase transition into consideration, is established based on the Henry model to calculate the gas solubility. To measure the degassing speeds with non-equilibrium phase transition and equilibrium phase transition respectively, degassing experiments are done at different pressure drop speeds with the oil-gas system composed of transformer oil and carbon dioxide. A function characterizing the non-equilibrium nature of the oil and gas system is derived after calculation and matching, based on which, degassing speeds and bubble point pressures at different pressure drop speeds are calculated. The impact of non-equilibrium phase transition on degassing and the deviation degree of the bubble point pressure are evaluated quantitatively. The model considering the non-equilibrium phase transition has higher computational accuracy than the Henry model not considering the non-equilibrium phase transition. The computation results indicate that the non-equilibrium phase transition reduces the bubble point pressure in the reservoir and slows down the degassing process of the volatile oil during the development of volatile oil reservoirs. The extent to which the non-equilibrium phase transition impacts degassing depends on the speed of pressure drop and the value of pressure drop: the bigger the pressure drop value and the faster the pressure drop speed, the more significant impact the non-equilibrium phase transition exerts on degassing, the lower the bubble point pressure and the slower the degassing speed. Key words: oil-gas system, volatile oil, non-equilibrium phase transition, degassing, model, solubility