With the rapid growth of energy consumption, enhanced oil recovery (EOR) methods are continually emerging, the most effective and widely used was polymer flooding. However, the shortcomings were gradually exposed. A novel decorated polyacrylamide might be a better alternative than polymer. In this work, the molecular structure and the properties reflecting the viscosity of decorated polyacrylamide, interfacial tension, and emulsification were examined. In order to better understand the interactions between decorated polyacrylamide and oil as well as the displacement mechanism, the displacement experiment were conducted in the etched-glass microscale model. Moreover, the coreflooding comparison experiments between decorated polyacrylamide and polymer were performed to investigate the displacement effect. The statistical analysis showed that the decorated polyacrylamide has excellent characteristics of salt tolerance, viscosity stability, and viscosification like polymer. Besides, the ability to reduce the interfacial tension in order 10⁻¹ and emulsification, which were more similar to surfactant. Therefore, the decorated polyacrylamide was a multifunctional polymer. The displacement process captured by camera illustrated that the decorated polyacrylamide flooded oil mainly by means of ‘pull and drag’, ‘entrainment’, and ‘bridging’, based on the mechanism of viscosifying, emulsifying, and viscoelasticity. The results of the coreflooding experiment indicated that the recovery of decorated polyacrylamide can be improved by approximately 11–16% after water flooding when the concentration was more than 800 mg/L, which was higher than that of conventional polymer flooding. It should be mentioned that a new injection mode of ‘concentration reduction multi-slug’ was first proposed, and it obtained an exciting result of increasing oil production and decreasing water-cut, the effect of conformance control was more significant.

The numerical simulation of hydraulic fracturing fracture propagation is the core content of hydraulic fracturing design and construction. Its simulation results directly affect the effect of fracturing, and can effectively guide the fracturing construction plan and reduce the construction risk. At present, two-dimensional or quasi-three-dimensional models are mainly used, but most of them are used to simulate the vertical fracture of hydraulic fracturing. There are errors in the application process. In this paper, a three-dimensional mathematical model, including an elastic rock mechanics equation and a material flow continuity equation, is established to simulate horizontal fracture propagation in shallow reservoirs. The emphasis of this paper is to propose a new method for solving equations. The basic idea of the iteration method has been proposed by previous scholars: Firstly, assuming that the initial pressure of each point in the fracture is uniform, the fracture height of each initial point can be obtained by using Equation (20). Using the initial height values, the pressure values at each point of continuous variation are calculated by Equation (16), and then the new fracture height values are obtained by Equation (20). Because of the equal initial pressure, this method leads to too many iterations in the later stages, which makes the calculation more complicated. In this paper, a new Picca iteration method is proposed. The iteration parameters are changed sequentially. Firstly, the distribution value of fracture height is assumed. Then, the pressure distribution value is calculated according to Equation (16). Then, the new distribution value of fracture height is obtained by bringing the obtained pressure distribution value into Equation (20). Then, the new distribution value of the fracture height is calculated according to Equation (16). The pressure distribution value completes an iteration process until the iteration satisfies the convergence condition. In addition, Sneddon’s model is introduced into the hypothesis of fracture height to obtain the maximum fracture height and assume that the initial fracture profile is a parabola. Finally, the proposed method can rapidly improve the convergence rate. Next, on the basis of investigating the solutions of previous equations, the Galerkin finite element method is used to solve the above equations. The new Picard iteration sequence method is applied to solve the height and pressure at different points in the fracture. By calculating the stress intensity factor, we can judge whether the fracture continues to extend or not, and then simulate the full three-dimensional horizontal fracture of the hydraulic fracturing expansion process. The infiltration process of three types of oil reservoirs in Daqing Changyuan oilfield is simulated. The results show that during the initial fracture stage, the radius and height of fractures increase rapidly, and the rate of increase slows down with the increase of construction time. The height and net pressure of each point in the fracture are unequal. The height and net pressure of the fracture in the wellbore reach the maximum, and gradually decrease to the front of the fracture. Compared with conventional fracturing, the fracturing-flooding percolation process has the characteristics of short fracture-making and large vertical percolation distance, which can greatly increase the swept volume of flooding fluid and thus enhance oil recovery. With the increase in the rock modulus of elasticity, the radius of fractures decreases and the height of fractures increases. With the increase in construction displacement, the radius of fractures hardly changes, the height of fractures increases, and the vertical infiltration distance of the fractures increases. It is suggested that the construction displacement should be 4.0 m³/min. In the range of fracturing fluid viscosity in the studied block, with the change of fracturing fluid viscosity, the change of fracture radius and height is not obvious. In order to further increase sweep volume, the fracturing fluid viscosity should be further reduced.

Heterogeneous artificial core plate models with low permeability are designed, made and evaluated based on similarity theory of heterogeneous reservoir with low-permeability physical simulation by artificial core plate model; then, simulative experiments for seepage flow patterns can be carried out. Pressure data are obtained by pressure transducers symmetrically arranged in artificial core plate models to study on the seepage flow patterns in heterogeneous reservoirs with low permeability. Experimental results show that the pressure gradient around injection and production points is high, and the pressure gradient of diagonal corner is very low. The distribution of pressure gradient changes as plane heterogeneity of artificial core plate models changes. The higher permeability increases the spread range of pressure, but the enhancement of heterogeneity has a negative effect on pressure transmission at the same time. The effect of permeability is greater than the negative impact of heterogeneous when the overall permeability of plate model is at a very low level. Non-seepage flow section becomes smaller with the increase in permeability, and the proportion of quasi-linear seepage flow section which is more conducive to fluid flow raise as seepage flow section becomes larger.

Surface-active polymer is a novel multifunctional active polymer applied for enhancing oil recovery which has both viscosity-increasing ability and surface activity. Experiments were carried out to indicate basic physicochemical properties of surface-active polymer and to study on differences of properties between surface-active polymer and other chemical flooding agents, and characteristics of increasing displacement efficiency by surface-active polymer flooding have been tested. Experimental results show that the molecular aggregation conformation, viscosity performance and flow capacity of surface-active polymer were significantly different from those of other chemical flooding agents. Positive effects of viscosity and viscoelastic properties and improvements in interfacial chemical properties are basic characteristics of increasing displacement efficiency by surface-active polymer flooding which are basic principles of surface-active polymer flooding for enhancing oil recovery.

Research progress of carbon dioxide applied for methane exploitation from hydrates is summarized, with a focus on advances in molecular dynamics simulations and their application in understanding the mechanism of carbon dioxide replacement for hydrate exploitation. The potential of carbon dioxide in enhancing energy recovery efficiency and promoting carbon capture and storage is emphasized. An overview is provided of the advancements made in utilizing carbon dioxide for methane hydrate exploitation, highlighting its significance. Subsequently, the theoretical foundations and techniques of molecular dynamics simulations are delved into, encompassing key elements such as statistical ensembles, molecular force fields, and numerical solution methods. Through simulations, various characterization parameters including mean square displacement, radial distribution functions, coordination numbers, angular order parameters, and hydrogen bonds are computed and analyzed, which are crucial for understanding the dynamic changes in hydrate structures and the replacement process. Thorough research and analysis have been conducted on the two possible and widely debated mechanisms involved in the replacement of methane hydrates by carbon dioxide, with a particular emphasis on guest molecular replacement and hydrate reconfiguration. These processes encompass the intricate interactions between carbon dioxide molecules and the cage-like structure of hydrates, as well as the rearrangement and stabilization of hydrate structures. Several key issues surrounding the application of carbon dioxide for methane hydrate exploitation are identified, including the influence of thermodynamic conditions, the selection of auxiliary gases, and other potential factors such as geological conditions and fluid properties. Addressing these issues is crucial for optimizing the extraction process and enhancing economic and environmental benefits. A theoretical foundation and technical reference for the application of carbon dioxide in methane hydrate exploitation are provided, while future research directions and priorities are also outlined.