An indoor horizontal experimental flow loop was constructed to investigate safe restart strategies for gathering pipelines in high-water-cut oil fields following unplanned shutdowns. The system enables cyclic shutdown-restart operations of oil-gas-water three-phase flow under varying conditions, with synchronous flow pattern visualization and high-frequency pressure/temperature data acquisition. Experiments revealed that a distinct horizontal oil-water stratification develops during shutdown. Based on this observation, a temperature drop prediction model was developed, which couples the external soil temperature field and explicitly accounts for the three-phase distribution. During restart, the reduction in flow area due to the gelled oil layer and its non‑Newtonian shear-shedding behavior are identified as the key mechanisms governing the pressure transients. Accordingly, a three-phase restart pressure prediction model was established by decomposing the total pressure into frictional pressure drop, gelled oil layer shear pressure drop, and inertial pressure drop. Experimental validation demonstrates that the coupled model can effectively predict the post‑shutdown temperature distribution and the full restart pressure evolution, including the peak pressure and subsequent decay.

As oilfield development progresses to its later stages, the produced fluid increasingly becomes high-water-cut crude oil. In such systems, the intricate interaction between oil and water phases results in viscosity being influenced by several factors, including temperature, water cut, and flow velocity, in a complex and interrelated manner. This complexity makes it challenging to precisely characterise the dynamic changes in viscosity. Traditional empirical correlation equations often fall short in accuracy and generalisation, particularly within the high-water-cut range. To address the need for accurate predictions of apparent viscosity, this paper introduces a prediction model based on a convolutional neural network optimised by particle swarm optimisation.Utilising viscosity data obtained through indoor loop experiments on a high-water-cut oil-water mixed system using a certain crude oil from China, this model integrates the number and size of convolution kernels with training hyperparameters, including learning rate, batch size, and training epochs, into the particle swarm global optimisation process. This method addresses parameter tuning issues in both the structure and training domains simultaneously, thereby enhancing convergence stability and accuracy in scenarios characterised by small samples and strong nonlinearity, surpassing manual or grid parameter tuning methods. Comparative evaluations with existing models, namely the Multilayer Perceptron and the Transformer, reveal that the proposed model achieves a superior coefficient of determination of 0.9420 and a root-mean-square error of 6.695, indicating significantly greater accuracy and robustness.

With the increasing adoption of flexible oilfield operations, inlet liquid-flow rate step changes intensify gas-liquid flow-regime transitions and inlet-pressure overshoots. Existing mechanistic models, primarily validated under steady conditions, often fail to reproduce the dynamic timing of pressure peaks under strong boundary disturbances. To address this, a pressure-based transient framework was developed based on a one-dimensional two-fluid model. Pressure-velocity coupling was achieved via a Semi-Implicit Method for Pressure-Linked Equations-like algorithm, incorporating closure relations for stratified and slug flows to capture the non-equilibrium evolution of the flow. Step-change experiments (0.1-1.0 Sm-3 h(-1)) were conducted at 30-60 degrees C and 85%-95% water cuts. Comparisons with Oil and Gas Simulator confirmed that while the model captures the overall transition trend (quasi-steady mean absolute percentage error <2.3%), it prematurely predicts the pressure peak with transient-stage errors up to 19.3%. Outlet liquid-holdup analyses reveal that this temporal discrepancy is physically rooted in the inertial lag of slug reconstruction, which the quasi-steady closure relations fail to encapsulate. Consequently, a physics-informed residual-correction method was proposed, utilizing weighted quadratic ridge regression to compensate for the missing unsteady interfacial mechanisms. After correction, the peak error was reduced to below 5.72%. This framework offers a reliable physics-data fusion tool for predicting transient responses of liquid flow step changes in horizontal pipelines under operational switching within the study scope.

Droplet electrodispersion is a fundamental phenomenon in various fields, such as electric demulsification, electrospray, and microfluidic manipulation. Electric-magnetic coupling technology, as an emerging noncontact method, shows substantial potential in modulating droplet electrohydrodynamics, yet the influence characteristics and mechanisms of coupled magnetic fields on droplet electrodispersion remain poorly understood. To address this gap, we conducted a detailed molecular dynamics simulation comparing the breakup dynamics of salt-containing droplets under a single electric field versus an electric-magnetic coupling field. Our results demonstrate that salty droplets in the electric-magnetic coupling field exhibit longer breakup response times and greater stretching deformation. This behavior is attributed to changes in ion migration speed and enrichment regions due to additional Lorentz forces. Furthermore, this effect of coupling field is observed only for ion numbers Nion > 0, with a marked attenuation at higher concentrations (Nion = 200), which is related to the hydration effect enhanced by magnetic field. When the electric capillary number Ca ranges from 0.88 to 3.91, the critical value triggering a shift in the breakup mode is enhanced in the coupling field. However, this effect diminishes as Ca approaches 8.8, at which point the coupled field no longer inhibits breakup. Additionally, as the dimensionless electric field frequency f* increases from 0.21 to 4.19, the ion migration trajectories become shorter and less able to accumulate at the interface, thereby limiting the effectiveness of the coupling field. Our study advances the fundamental understanding of salt-containing droplet breakup dynamics under an electric-magnetic coupling field and provides novel insights for controlling and suppressing electrodispersion in related technologies.

Foam pigs are widely used in the progressive pigging operation for reducing the wax buildup in crude oil pipelines. However, there is no investigation on the theoretical pigging model for foam pigs. To calculate the pigging force and the efficiency of foam pigs, a pigging model for foam pigs is established. The foam pig's displacement during deformation is calculated under linear elastic and elastic buckling. The slip line field theory is used to deduce the stress distribution within the wax plastic zone. The effect of energy absorption is taken into account in the modeling of the pigging force due to the low-density foam pig's extraordinary ability to absorb energy. According to the pigging tests, there are average relative errors of 19.49% and 9.25% between calculated and experimental values for the pigging force and efficiency, respectively. Furthermore, the wax blockage accident of LP pipeline is analyzed and used to validate the model. In the validation, actual and calculated values for the pressure drop and pigging efficiency are compared. It is indicated that the prediction error of the proposed model for pigging efficiency is 41.0%.

Electrocoalescence technology can efficiently dehydrate waxy crude oil but the mechanisms are still unclear. Herein, the continuous microscopic behaviors of droplet falling, deformation, and coalescence were experimentally investigated to clarify the dynamic response mechanism of droplet in waxy oil under an electric field. The results showed the droplet falling under both gravity and electrostatic attraction to deform by the electric field force. Moreover, the expansion and clamping of the liquid bridge resulted from the competition between electric field force and capillary force. However, the precipitated wax crystals reduced the kinetic energy of the droplet and affected its external circulation, thus delaying the falling time. In addition, the wax crystals with interfacial activity adsorbed on the oil-water interface and cross-linked to form a spatial network structure, thereby weakening droplet deformation, hindering liquid film drainage, and inhibiting liquid bridge expansion. Importantly, the droplet adsorbed wax crystals exhibited interfacial elasticity, which makes them more inclined to partial coalescence. The low-frequency pulsed direct current (PUDC) electric field with high strength intermittent effect displayed the most obvious inhibition effect on the wax crystals. Overall, these findings look promising for future design and optimization of high-efficiency electric dehydrators and related fields.

Droplet-interface electrocoalescence is a common dynamic behavior in many industrial applications, especially in the oil-water separation process in the petroleum industry. However, the underlying mechanism of the dynamic response in the droplet-interface coalescence process under the sinusoidal alternating current (sine AC) field is not fully understood. In this paper, the combination of the finite element method and the Level-Set method was used to conduct numerical simulation research on two typical coalescence modes of droplet-interface coalescence under the sine AC electric field. The dynamic response behavior of the droplet and interface was systematically analyzed in terms of charge transfer, pressure field distribution, and flow field evolution. The results showed that the weakening effect of electric field force duration due to charge transfer was an important reason for AC electric field to accelerate coalescence, and the rearrangement of charges at the liquid bridge was the key influencing factor for partial coalescence. In addition, the occurrence of the transfer of high-pressure region from droplet to liquid bridge occurs is a critical factor in the determination of the two typical coalescence modes. Moreover, the induced force between the vortex pairs contributed to the collapse of the upheaval in complete coalescence. The interaction between the vortex pairs and the droplet’s internal circulation in the flow field triggered the release of the secondary droplet in partial coalescence mode. Finally, through the nondimensionalization of coalescence factors and the evaluation of transition modes, it is verified that the increase in electric field frequency was more conducive to the occurrence of complete coalescence. These findings are useful for the design and optimization of the high-efficiency electric dehydrator and research in related fields.

Under high-strength electric fields, partial coalescence may occur, thus producing fine secondary droplets, which are undesirable for separating water from oil. In this study, experimental and numerical methods are employed to investigate the coalescence behavior under a DC electric field to comprehensively understand the effect of electric field strength (E) and droplet diameter (D) on coalescence. The Level-set method is employed to capture the moving interface, and the numerical data are validated through experimental tests. The results reveal the easy formation of secondary droplets with increasing E and D values. In particular, the electric field strength suppresses the expansion of the liquid bridge and hinders the vertical collapse of the droplets. The distortion of the electric field at the liquid bridge and the polarized charge both increase with E, thus resulting in stronger electric field repulsion. Moreover, the enhancement in D significantly affects the shrinkage of the liquid bridge and prevents the vertical collapse of the droplet. The pressure gradient at the liquid bridge from the outside to inside decreases as a function of D, thereby inhibiting the contraction speed. Furthermore, the number of polarized charges concentrated on the top of the droplet increases, thus resulting in an enhanced electric field tension. The results obtained herein can potentially act as guide for the design and optimization of electric dehydrators.

Pigging technology is frequently employed to minimize the potential risk of wax deposition for the safe operation of subsea pipelines, but a limited understanding of the flow of fractured wax deposits heightens the blockage hazard of mechanical pigging operations and lacks a scientific basis for determining the pigging frequency. In this paper, a series of rheological experiments were carried out by a vane-in-cup geometry, and the flow of fractured wax deposits was uncovered by an in-house pigging apparatus. It was found that slight thixotropy and viscoplasticity dominated the rheological behavior of the fractured wax deposit. In addition, the weak thixotropy, which accounts for the local resistance to wax plug flow, remains constant from plug formation to discharge. The in-house pigging experiments also revealed that the local resistance is only related to the static yield stress of the wax deposit and the pigging speed, both of which are independent variables of the microstructural configuration. Drawing on microstructural changes to quantify the effect of shear history, a physical model was formulated to predict the local resistance to wax plug flow under various pigging conditions. The model predictions deviate within acceptable limits from the experimental matrix and data reported in the literature. In addition, the concept of safe maximum differential pressure was introduced to assess the occurrence of wax plugging accidents as well as to determine the upper threshold of the pigging frequency for subsea pipelines.

Exposing waxy oils to an electric field may significantly improve their cold flowability. Our previous study has shown that interfacial polarization, i.e., charged particle accumulation on the wax particle surface, is the primary mechanism of the electrorheological behavior of waxy oils. However, the way that charged particles interact with wax particles under an electric field remains unknown. In this study, we found no viscosity and impedance change for two waxy crude oils after their exposure to a high-voltage electric field. However, the yield stresses were reduced obviously. We thus proposed that the collision of colloidal particles such as resins and asphaltenes with the wax particles could be an essential mechanism that the wax particle structure was weakened. To verify this hypothesis, a series of ad hoc experiments were carried out, i.e., by performing electrorheological tests on model waxy oils containing additives removable under an electric field, including electrically-neutral colloidal particles (Fe3O4), charged colloidal particles (resins), and oil-soluble electrolyte (C22H14CoO4), respectively, and demonstrated that upon application of a high-voltage electric field, charged particles in a waxy oil may move and thus collide with wax particles, and consequently adhere to the wax particle surface. The particle collision results in damage to the wax particle network, and the electrostatic repulsion arising from the adhesion of the charged particle on the wax particle diminishes attraction between wax particles. This study clarifies the process of interfacial polarization.

High-voltage electric field treatment is an emerging approach to improve the cold flowability of crude oil, of which the physical principle is the negative electrorheological effect of crude oil other than electric heating and electric field dehydration. Based on the review of literatures on electrorheology, several mechanisms of negative electrorheological effect were summarized, and the problems in the electric field treatment mechanisms of crude oil, such as particle aggregation into chains, increasing the particle size of wax crystal, and enhancing the polydispersity, were analyzed. Besides, the basis of wax particle interface polarization was explained. Generally, the co-existence of wax particles, resins and asphaltenes is the necessary condition to realize the treatment effect of electric field. When a high-voltage electric field is applied, the charged particles(i.e. the resins and asphaltenes) in the crude oil would aggregate on the surface of wax crystal, which is the interface polarization. During the process, the electrostatic repulsion between wax particles is increased while their attraction is weakened, resulting in improved cold flowability of the crude oil. Therefore, the behavior of resins and asphaltenes in the oil is the key to understand the mechanism of the negative electrorheological effect of crude oil, which mainly includes three processes: the migration of resins and asphaltenes from the bulk phase to wax particles upon the application of electric field,accumulation of resins and asphaltenes on the surface of wax particles, and their diffusion back to the bulk phase after the removal of electric field. In the future, further in-depth and quantitative research should be focused on these three processes to fully reveal the scientific mechanism of the electrorheological effect of crude oil.

Electric field treatment is a new method to improve the cold flowability of waxy crude oil. Its basic principle is electrorheological behaviors of waxy oil, and its mechanism is the interfacial polarization of wax particles. So far, researchers have found that the effect of electric field treatment varies greatly among different crude oils, yet the mechanism is unclear. Herein, the effect of electric field treatment on improving flowability was tested using 8 waxy crude oils with various resin and asphaltene contents ranging within 4% to 23%. The results show that: under the experimental conditions, the crude oils with lower resin and asphaltene content (of which the total mass fraction is less than 5%) have the viscosity reduction effect induced by electric field increase first and then decrease with the increasing of cumulative amount of wax precipitated; the crude oils with medium resin and asphaltene content (of which the total mass fraction is about 10%) have the viscosity reduction effect induced by electric field increase monotonically with the increasing of precipitated wax; the crude oils with high resin and asphaltene content (of which the total mass fraction is above 15%) have unobvious viscosity reduction effect induced by electric field. It is concluded according to the mechanism of interfacial polarization of wax crystal particles of flowability improvement by electric field treatment is closely related to the abundance and aggregation degree of rein and asphaltene in crude oil.

Applying an electric field to waxy oil may significantly improve its cold flowability. Our previous study has demonstrated that the accumulation of asphaltenes and resins on the surface of wax particles, i.e., interfacial polarization of wax particles, is the essential mechanism of this electrorheological phenomenon. The influence of asphaltenes concentration on the performance of the electrical treatment has been studied. In this paper, the influence of the concentration of resins, the most abundant non-hydrocarbon component in crude oil, on electrically-treated waxy oil's viscosity and impedance was investigated for the first time by using model oils containing resins in the concentration range of 0.05 wt% - 5.00 wt%. It is found that the effect of resins concentration on viscosity and impedance is not monotonous, with both the viscosity reduction and impedance increment induced by the electric field decreased first and then increased with increasing resins concentration at a given amount of precipitated wax. Increasing the polarity of resins would alleviate the viscosity reduction and impedance increment. This work further demonstrates that resins accumulation on the wax particles surface does occur.

Treatment with pour point depressant (PPD) can significantly improve the cold flowability of waxy crude oil, enabling the safe and efficient transportation of waxy crude oils through pipelines. It has been observed that the electrical properties of waxy oil, such as the dielectric constant, zeta-potential, etc., change upon PPD treatment. In a previous study, we reported that wax precipitation results in a significant change of impedance spectroscopy (IS) of a waxy oil, i.e., a second semicircle appears in the Nyquist diagram and becomes increasingly bigger with increasing amount of precipitated wax. In this study, we found that the addition of PPD may significantly reduce the second semicircle, and the more effective the PPD is, the more reduced the second semicircle will be. Equivalent circuit models suggest that the impedance characteristics of the liquid phase of wax-in-oil suspension change little with PPD addition, but the capacitance of wax particles increases and the resistance of wax particles decreases significantly. A positive correlation between the viscosity reduction and the reduction of resistance of wax particles caused by PPD is discovered. After PPD treatment, the polar functional groups in PPD molecules potentially induce charge on wax particles as they precipitate, causing the relationship between the viscosity and conductivity to approach the fractional Walden rule. This work explains the reason for the improvement of flowability upon PPD addition from a perspective of IS, which provides some new proofs to understanding the functional mechanism of PPD.

Previous studies have shown that the application of a high-voltage electric field to a liquid or gelled waxy crude oil can significantly improve its cold flowability, such as reducing viscosity and yield strength. However, the mechanism of the electrorheological behaviors of waxy oils remains largely unknown. In this study, the impedance spectroscopy was firstly used to investigate the mechanism of the electrorheological behaviors of waxy oils. The impedance of the waxy oil increases and the conductivity decreases after an oil is exposed to electric fields. Based on this finding and with the aid of further experiments using model oils of controlled compositions, i.e. to control the absence of wax, resins and asphaltenes in the oil, interfacial polarization of wax particles was demonstrated as the primary and essential mechanism of the electrorheological behaviors. The interfacial polarization of wax particles means that charged colloidal particles in the oil, i.e., resins and asphaltenes, would accumulate on the surface of wax particles upon the application of the external electric field, and the resulted electrostatic repulsion will diminish the van der Waals force between wax particles, thus reducing viscosity and the strength of wax particle structure. (C)& nbsp;2021 Elsevier Ltd. All rights reserved.

The paraffin molecules in crude oil crystalize and precipitate out as the oil cools, resulting in a sharp increase in oil viscosity and further the gelation of the oil. The waxy crude oil gel exhibits complex rheological behaviors, such as viscoelasticity, yield stress, and thixotropy, posing challenges to the flow assurance of pipelines. Previous studies have verified that applying a high-voltage electric field to a flowing liquid oil can significantly reduce its viscosity. In this work, the electrorheological behaviors of waxy crude oil gel are explored by a stress-controlled rheometer equipped with in situ DC electric field manipulation. It is reported for the first time that the gel structure can be significantly weakened upon the application of an electric field for a duration of not less than 10 s, with the yield stress, storage modulus, loss modulus, and apparent viscosity reduced by up to 90%. In addition, the gel structure fracture is observed to transit from brittle-like to ductile-like. A stronger structure weakening effect can be obtained at a higher field strength and lower temperature. The structure weakening effect induced by the electric field can be maintained for a certain period of time after the removal of the electric field, with a recovery of yield stress and moduli less than 10% in 48 h. We hold the view that the electrorheological behaviors of waxy oil should be attributed to the weakened attraction between wax particles induced by the electric field.

Recent studies have shown that the poor flowability of waxy crude oil can be obviously improved by the application of an external electric field. Available studies about this novel technique to treat waxy oils focus on the efficacy of this technique while the sustainability of the efficacy is not well understood. In this work, the impacts of shearing and thermal cycling on the stability of the electric treatment efficacy were investigated. A representative waxy crude treated by electric field was subjected to shearing at different conditions and reheating to an elevated temperature and cooling, then the viscosity and the yield stress were inspected and wax particle microscopic images were observed to examine the impacts of shear and thermal histories on the sustainability of waxy crude oil flowability improvement by electric treatment. The experimental results show that the electric treatment efficacy of waxy crude oil gradually diminishes after the removal of electric field. However, shearing at a high shear rate and for a prolonged duration partially preserves the efficacy of the electric treatment and intensively shearing the electric treated oil provides some additional flowability improvement. The flowability improvement by electric treatment is weakened by reheating the treated oil to an elevated temperature. When the treated oil is heated above the wax dissolution temperature, the efficacy of the electric treatment is eventually eliminated. The results presented in this work further the understanding of the flowability improvement of waxy crudes by electric treatment.

由于页岩油及致密油在开发方式和生产规律等方面与常规油藏存在较大差异,采用传统的地面工程建设技术难以满足高效开发的要求.在全面总结页岩油及致密油单井和区块的开发和生产规律的基础上,从地面工程建设角度划分了单井和区块的生产阶段,结合开发和生产特点,提出了"统筹优化、骨架先行、模块组合、集成橇装、分期匹配、搬迁复用、集中处理"的地面工程标准化、模块化建设模式,以及单井计量、集输、采出液处理、返排液及采出水处理采用的地面工艺技术.可以降低地面建设投资和运行成本,提高整体开发效益.

Modification of crude oil is a basic method to improve the safety and economy of pipeline transportation. Definitely, high-voltage electric field treatment is a new approach to modify the crude oil based on its electrorheological effect. Herein, the progress of research on electric field treatment for modification of crude oil was summarized systematically, and the law of the electrorheological effect of crude oil was also concluded. The research results indicate that: applying an electric field (with an intensity of 0.2-5 kV/mm) to crude oil for several seconds can obtain the significant immediate modification effect. Specifically, the viscosity and yield stress can be reduced at a rate of 80% or higher, but the energy consumption is only 1% of that required for the same viscosity reduction rate by heating. After the removal of electric field, the viscosity and yield stress will recover gradually. The effect of viscosity reduction will disappear after about one day of placement. But the yield stress recovers slowly (at 90% of the reduction rate of yield stress two days later). The modification effect of electric field treatment is closely related to the composition of crude oil, and the presence of wax crystal, resin and asphaltene in the crude oil is essential for electric field treatment. In addition, the existing issues of the current research on electric field treatment technology were analyzed, and the development direction of the technology in the future was also proposed.

阻抗谱或者介电谱测量是一种迅速的、非侵入的测量手段.国外的石油方向研究学者对介电技术的应用十分广泛.本文针对原油生产与运输中常见的问题,综述了介电谱在石油科学领域的研究进展:沥青质发生聚集或者絮凝前后,油样的介电性质会发生显著变化;原油乳状液稳定性与其电学性质密切相关;原油的流动性质与其电学性质之间存在定量关系.最后本文推荐了今后研究的方向:介电的角度研究蜡对原油流变性质的影响.