Oil production is a complex process that can be made more efficient by applying gas enhanced oil recovery (EOR) methods. Thus, it is essential to know the minimum miscibility pressure (MMP) and minimum miscibility enrichment (MME) of gas in oil. Conventional slim-tube experiments for the measurement of MMP require hundreds of millilitres of real or recombined oil and last over 30 days. Advances in microfluidic technology allow the reduction of the amount of fluid and the time required in determining MMP (or MME), hence making the process rapid. In this study, we developed a microfluidic model with a stochastically distributed pore network, porosity of 74.6% and volume of 83.26 nanolitres. Although the volume was six orders of magnitude smaller than the slim tube, it retained the same proportions, guaranteeing a proper comparison between the tests. This microfluidic chip allowed the study of the MMP of n-decane with carbon dioxide at two different temperature conditions. The experimental results coincided with the results received both from conventional and microfluidic experiments. Furthermore, a numerical simulation of a section of the microfluidic model under the experimental conditions presented results within acceptable margins of the experimental ones. The results of the presented methodology indicate the potential to replace conventional technology for the measurement of MMP with microfluidic technology. Its promise lies in accelerating laboratory tests and increasing the reliability of experimental results and, subsequently, the quality of field gas EOR operations.

To increase the oil recovery factor (RF), enhanced oil recovery (EOR) methods are applied: chemical, gas, thermal, and combined ones. Standard laboratory research methods for selecting and optimizing EOR technologies require a lot of time and resources, as well as core material, which is often in short supply. To optimize the selection of reagents and field development technologies, the use of microfluidic technology is proposed i.e. conducting experiments in reservoir conditions using microfluidic chips with a porous structure, reproducing the properties of the core of the target field. The main advantages of conducting tests in micromodels are the low duration and the ability to visualize filtration processes, which makes it possible to evaluate the behavior of fluids in reservoir conditions. This paper considers the modern application of microfluidics for the selection of EOR agents and stimulation 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 low-mineralized water action is described. Conducting microfluidic tests to optimize gas and thermal EOR, which became possible due to the development and improvement of technology, is considered.

Most of the reservoirs today are mature, and traditional waterflooding is not enough for the effective development of oil formations. One of the ways to significantly increase production efficiency for deep, low permeable reservoirs is gas EOR (enhanced oil recovery) methods. This paper presents a method for screening and increasing efficiency of gas EOR methods based on microfluidic studies and for studying the influence of various factors on the oil displacement process. Such technology can be used on par with traditional core flooding tests, reducing time, cost, and the amount of needed fluid. The porous structure was realized as a silicon-glass microchip that can withstand high pressure and temperature close to the reservoir conditions. For the tests, n-decane was chosen as a model oil phase, while nitrogen was used along with carbon dioxide for screening. On the microchips, several tests were done that proved the approach's effectiveness for screening gases before field application. The most effective for carbon dioxide occurred miscible displacement, resulting in the almost complete displacement of n-decane. Additionally, when comparing tests with the same system pressure but a different pressure drop, a more considerable drop led to a higher oil recovery coefficient. Since the conventional nitrogen injection resulted in an insignificant displacement coefficient even after an increase in differential pressure, it was decided to use this agent for the huff-n-puff injection experiment. The test led to the raising of the sweep efficiency coefficient by two times. Thus, an experimental procedure and a unique microchip geometry with the radial homogenous porous structure were developed, allowing tests to be performed for both conventional gas flooding imitating a five-spot pattern and huff-n-puff gas injection.

Surfactant flooding is among the most studied and widespread EOR technologies that is being introduced into tight and low-permeable reservoirs to mobilize trapped oil. Typically, the selection of formulations for chemical flooding is associated with numerous challenges and constraints such as time-consuming core flooding tests, the high cost of the tests with modern saturation control methods, and a limited amount of core samples. To overcome these issues, microfluidic technology was applied to optimize the screening of surfactant compositions for flooding. The workflow of this project consisted of five main steps: (1) fabrication of microfluidic chips, (2) surfactant screening in bulk, (3) surfactant flooding in microfluidic chips, (4) image analysis and data interpretation. Silicon-glass microfluidic chips, which are 2D representatives of the reservoir porous media, were used in the experiments. The porous structure geometry was developed based on CT images of core samples from a particular field with low permeability. For the selected surfactants, interfacial behavior on the boundary with n-decane was studied and correlated with hydrocarbon recovery ability. The results obtained revealed that the IFT patterns have a significant influence on displacement efficiency. Thus, the surfactant compositions with a lower initial IFT than the equilibrium value achieved higher recovery factors.