Conventional assumptions about multiphase flow in gas condensate reservoirs often do not correlate with field production. This discrepancy stems from the various mechanisms influencing the multiphase process, which are inadequately represented in numerical models. One of the least understood mechanisms is the influence of the non‑equilibrium thermodynamics on the flow in the wellbore region, where the reservoir pressure is below the dew point pressure. To address this problem, experimental and mathematical analyses were conducted using a microfluidic device designed to replicate the flow dynamics in a gas condensate system.

Conventional assumptions about multiphase flow in gas condensate reservoirs often do not correlate with field production. This discrepancy stems from the various mechanisms influencing the multiphase process, which are inadequately represented in numerical models. One of the least understood mechanisms is the influence of the non‑equilibrium thermodynamics on the flow in the wellbore region, where the reservoir pressure is below the dew point pressure. To address this problem, experimental and mathematical analyses were conducted using a microfluidic device designed to replicate the flow dynamics in a gas condensate system.

The exploration of gas condensates poses challenges due to complex multiphase flow mechanisms, especially below the dew point pressure. Existing assumptions about multiphase flow under these conditions do not align with actual field production. To address this, a microfluidic experiment was conducted to replicate the flow dynamics of gas condensate systems. Furthermore, a mathematical analysis was conducted to account for the deviation of the flow from the traditional assumptions of local equilibrium. The results showed significant deviations in condensate phase saturation from traditional local equilibrium assumptions. This deviation is mainly due to the non-instantaneous phase separation of the condensate phase. Hence, the condensate flows as a sub-critical nuclei in the gas phase (fog state).

Introduction
Currently, the oil industry often faces the challenge of correctly selecting the agent introduced into the reservoir to increase oil production. For many years, the main standard has been laboratory tests on core samples, assuming that all cores are slightly different from each other. However, samples are often heterogeneous and, worse, not reusable. This means that a new core is needed for each test, which can lead to very low accuracy in selecting an EOR agent.
Microfluidic chips represent a unique alternative to core research. In the case of microchips, one design can be reproduced many times, ensuring the testing of various liquids and gases under the same conditions, and accurate assessment of a particular technology for the chosen reservoir. Currently, there is no standard procedure for creating microfluidic analogs of real deposits. Therefore, the idea of this research is to develop such a methodology to accelerate it.

To increase the oil recovery factor, enhanced oil recovery methods (EOR) are used: chemical, gas, thermal, and combined. Standard methods of laboratory research for the selection and optimization of EOR technologies and inflow intensification require significant time and resource expenditures, as well as core material, which is often in short supply. The application of microfluidic technology, i.e., conducting experiments under reservoir conditions using microfluidic chips with a porous structure reproducing the properties of the target deposit's core, is proposed to optimize the selection of agents and development technologies. The main advantages of conducting tests in micromodels are low duration and the ability to visualize filtration processes, which allows assessing the behavior of fluids under reservoir conditions.
This work considers the modern application of microfluidics for the selection of EOR agents and inflow intensification methods and the status of this technology in the oil and gas industry. The use of microfluidic chips for screening surfactants and polymers, as well as studying the mechanism of action of low-mineralized water, is described. Microfluidic tests for optimizing gas and thermal EOR were conducted, made possible by the development and improvement of technology.

Oil extraction is a complex process that can be made more efficient through the application of enhanced oil recovery (EOR) methods using gas. Thus, it is extremely important to know the minimum miscibility pressure (MMP) and minimum enrichment by miscibility (MME) of gas in oil. Traditional experiments in slim tubes to measure MMP require hundreds of milliliters of real or recombined oil and last more than 30 days. Advances in microfluidic technology allow reducing the amount of fluid needed and the time required to determine MMP (or MME), thereby accelerating the process. In this study, we developed a microfluidic model with a stochastically distributed network of pores, a porosity of 74.6%, and a volume of 83.26 nanoliters. Although the volume was six orders of magnitude smaller than that of a slim tube, it maintained the same proportions, ensuring a correct comparison of tests. This microfluidic chip allowed the study of MMP of n-decane with carbon dioxide under two different temperature conditions. Experimental results matched those obtained from both traditional and microfluidic experiments. Additionally, numerical modeling of part of the microfluidic model under experimental conditions showed results within the acceptable limits of experimental data. The results of the presented methodology indicate the potential to replace traditional MMP measurement technologies with microfluidic technology. Its promise lies in speeding up laboratory tests and improving the reliability of experimental results and, subsequently, the quality of field operations for enhancing oil recovery using gas.

Polymer flooding is one of the most studied and widely applied enhanced oil recovery (EOR) technologies, implemented in tight and low-permeability reservoirs to mobilize trapped oil. Typically, the selection of chemical compositions for polymer flooding is associated with numerous challenges and limitations, such as time-consuming core flooding tests, high costs of testing with modern saturation control methods, and a limited number of core samples available. To overcome these challenges, microfluidic technology was applied to optimize the screening of surfactant compositions for flooding. The workflow of this project consisted of five main stages: (1) manufacturing of microfluidic chips, (2) volume screening of surfactants, (3) polymer flooding in microfluidic chips, (4) image analysis, and data interpretation.
For the experiments, silicon-glass microfluidic chips were used, which are 2D representatives of the porous medium of a reservoir. The geometry of the porous structure was designed based on CT images of core samples from a specific low-permeability field. The interfacial behavior of selected surfactants at the boundary with n-decane was studied and correlated with their ability to recover hydrocarbons. The results showed that patterns of interfacial tension significantly impact the efficiency of displacement. Thus, surfactants

Most of today's fields are mature, and traditional waterflooding is insufficient for effective development of oil layers. One way to significantly enhance the extraction efficiency for deep, low-permeability fields is through the use of gas-enhanced oil recovery (EOR) methods. This work presents a screening method and an efficiency improvement of gas EOR methods based on microfluidic research, as well as studying the impact of various factors on the oil displacement process. Such technology can be used alongside traditional core flooding tests, reducing time, cost, and the amount of fluid required. The porous structure was implemented in the form of a silicon-glass microchip that can withstand high pressure and temperature, close to field conditions. N-decane was chosen as the model oil phase for the tests, while nitrogen was used along with carbon dioxide for screening. Several tests conducted on the microchips proved the effectiveness of this approach for screening gases before application in field conditions. Miscible displacement proved to be the most effective for carbon dioxide, leading to almost complete displacement of n-decane. Additionally, when comparing tests with the same system pressure but different pressure drops, a greater drop led to a higher oil recovery factor. Since traditional nitrogen injection resulted in a negligible displacement factor even after increasing the differential pressure, it was decided to use this agent for an experiment with pulsating introduction. The test led to a doubling of the sweep efficiency factor. Thus, an experimental procedure and a unique geometry of the microchip with a radial uniform porous structure were developed, allowing the tests to be conducted.