The use of a surfactant solution during oil and gas field development might improve the recovery rate of oil reservoirs. However, the serious emulsification of the produced liquid will bring challenges to the subsequent treatment process and storage and transportation. It is urgent to understand the coalescence mechanism of crude oil under the action of surfactant solution. This research investigates the coalescence mechanism of numerous oil droplets under liquid flow perturbation. The model was established to study the coalescence process of multiple oil droplets. The effects of the number of oil droplets under homogeneous conditions, the size of oil droplets, and the distance between oil droplets under non-homogeneous conditions on the coalescence process were analyzed. Meanwhile, the change rules of the completion time of oil droplet coalescence were drawn. The results show that the smaller the size of individual oil droplets under non-homogeneous conditions, the longer the coalescence completion time is, and when the size of individual oil droplets reaches the nanometer scale, the time for coalescence of oil droplets is dramatically prolonged. Compared to static circumstances, the time it takes for oil droplets to coalesce is somewhat shorter under gravity. In the fluid flow process, in the laminar flow zone, the coalescence time of oil droplets decreases with the increase of the liquid flow rate. However, in the turbulent flow zone, the coalescence time of oil droplets increases with the increase in the liquid flow rate. The coalescence time is in the range of 600~1000 ms in the flow rate of 0.05~0.2 m/s. In the presence of surfactants, the oil content in the emulsion system increases under the influence of pumping flow. The change in oil content rate with various surfactants is less impacted by flow rate, owing to the stable emulsion structure created by the extracted fluid within the reservoir. The study findings presented in this research provide technical assistance for effective crude oil storage and transportation.

Fracturing technology is an important technique in the development of shale reservoirs. Compared with conventional hydraulic fracturing, explosive fracturing technology has the advantages of low cost and environmental protection. Relevant research results have shown that this technology can effectively improve the efficiency of shale oil and gas extraction. To further reveal the mechanism of reservoir fracture propagation under explosive fracturing, this paper conducted experimental research on the propagation law of complex fractures in shale reservoirs under impact load. The dynamic elastic modulus of shale samples was tested by using the Split Hopkinson Pressure Bar (SHPB) test system. A finite element model was established by using LS-DYNA software. Based on test results, the fracture propagation process was simulated under different impact loads, interlayer spacing, and fracture distribution conditions. The results indicate that the original crack zone of layered reservoirs is more prone to induce stress, which is beneficial for reservoir transformation in the near wellbore area, while explosive fracturing. The increase in interlayer spacing is beneficial for the expansion of the main crack, which can improve reservoir connectivity. As the impact load increases, the main cracks have better connectivity. This study can provide a theoretical basis for optimizing fracturing parameters and designing fracturing schemes, which is of great significance for the promotion of explosive fracturing technology and the efficient and environmentally friendly development of shale oil.

Based on the existing research results, a theoretical fracture model of strata under the compound impact of static and harmonic dynamic load is improved, and the fracture characteristic parameters (stress intensity factor, T-stress, and fracture initiation angle) under the two far-field stress are determined according to the crack dip angle. Additionally, the effects of harmonic dynamic load on the distribution of the stress field and the fracture characteristic (the crack initiation angle, the fracture degree, the number of fracture units, and the fracture area) are further calculated and discussed by theoretical model solution, extended finite element simulation, and the secondary development of the simulation module, respectively. The research results show that the far-field stress, stress intensity factor, and T-stress vary in harmonic form with time under the compound impact of static and harmonic dynamic loads. The frequency of dynamic load affects the number of reciprocal fluctuations of stress intensity factor and T-stress as well as the crack initiation time, but has less influence on the crack initiation angle and fracture degree. While the amplitude of dynamic load affects the stress intensity factor, the extreme value of T-stress and fracture characteristics of the crack. This study has theoretical guiding significance for parameters’ optimization and realization of resonance impact drilling technology.