The spread behaviors of the underwater oil droplet on smooth brass substrate were studied using high⁃speed microscopic imaging technology. Chemical and physical modifications were made on the surface of the brass sheet to change its surface properties, and the controllable regulation of superoleophilic–superoleophobic wettability gradient of the surface was achieved successfully. The spreading length and contact angle of the oil droplet rising to different modified surfaces were tested. Different from that in air condition, influence of water surrounding the oil droplet must be considered, which is complicated in water. In this work, on the basis of the energy conservation mechanism, quantitative relationship among the eigenvalues for the spreading behaviors of the oil droplet rising to the surfaces, such as droplet dimensionless spreading length, the droplet impact velocity, droplet size, droplet properties, viscosity of the water and surface wettability, were obtained. An optimized spreading dynamic model was constructed to describe the spreading behaviors of underwater oil droplets on surfaces with different wetting properties, to give support for the design of new oil⁃water separation equipment.

The dispersion characteristics of droplets in swirling turbulent flow field is a difficult problem in the process of fluid mechanical design and optimization. A new concentric rotating cylinder is used to obtain uniformly distributed flow field. On the basis of Hinze's model, the influence of oil droplet viscosity on oil droplet dispersion characteristics is considered. The relationship between turbulent flow field and oil droplet dispersion characteristics is preliminarily discussed. The empirical relationship between flow field characteristics and oil droplet dispersion characteristics is obtained when Reynolds number is 5.5×104~2.4×105 and relative centrifugal force is 21.9~643.3.The research on dispersion characteristics of oil and water in swirling turbulent field is improved, which provides a new research idea for the liquid⁃liquid dispersion characteristics in swirling turbulent flow field.

In order to investigate the phenomenon of gas⁃liquid bias in parallel separators in oil⁃gas gathering and transportation system, an experiment facility for gas⁃liquid two⁃phase splitting was designed, constructed and instrumented. Flow rates, pressure, pressure drop，liquid level and liquid holdup were measured and recorded by data⁃acquisition system. Gas⁃liquid splitting pipelines of two geometries (horizontal pipeline⁃T junction⁃ horizontal pipeline and horizontal pipeline⁃T junction⁃vertical pipeline) were constructed. Experiments on splitting of slug flow were carried out and splitting characteristics of gas⁃liquid were studied with symmetrical and asymmetrical pipeline conditions. When the pipeline conditions are symmetrical, the two phases of slug flow splitting into two separators are even for pipelines of two geometries. When the pipeline conditions at the outlets of separators are asymmetrical, mal⁃distribution of both two phases occurs and liquid tends to split more evenly than gas. Based on the calculation of pressure drop, a splitting model was established and the influence of gas⁃liquid velocity on the flow characteristics was explained simply.

The offshore natural gas condensate wellhead platform has the characteristics of limited space, far from land, no permanent staff and high maintenance cost, which poses a higher challenge to the desanding equipment and technology. In order to solve this problem, a compact tubular sand removal equipment with small volume is proposed.The performance of the sand removal device is evaluated with pressure drop, mass separation efficiency and particle separation efficiency as evaluation indicators. The results show that the mass separation efficiency increases rapidly in the process of the separation chamber diameter changing from D1 to 2D1. Continuing to expand the diameter of separation chamber, the increasing trend of mass separation efficiency decreases and the pressure drop of sand remover increases rapidly; The desander with two⁃stage separation structure has obvious improvement in separation performance, and the mass separation efficiency has been increased by more than 20%. Comparing the particle size of separated gravel with the critical particle size of pipeline carrying sand and the critical particle size of wellhead safe operation, it can be concluded that the separation efficiency of large grain gravel can reach more than 80%, and the tubular desander can complete the pre⁃separation task of offshore wellhead platform gravel.

It is one of the important tasks to perform the necessary liquid loading treatment in the daily operation and management of wet gas pipeline. Based on the transient simulation method of pigging process in OLGA software, the development process prediction model of liquid loading in wet gas pipeline was established. The law of liquid loading deposition and development in wet gas pipeline were analyzed. In the end, the design and simulation of a novel liquid loading treatment scheme was carried out. It is pointed out that adding separation devices between wet gas pipelines can significantly reduce the amount of liquid loading and prolong the liquid loading development duration, which plays a positive role in reducing the frequency of pigging and optimizing the volume of terminal treatment devices. Under the same capacity and constant pressure constraints in the end of the pipeline, the separation device between wet gas pipeline can effectively reduce the power demand in the starting point of pipeline, which is conducive to energy saving and consumption reduction of the overall process flow.

Non⁃metallic pipeline has become the new direction of oil and gas pipeline technology because of its excellent performance. However, the electrostatic problem during the oil transportation process threatens the safe operation of pipeline. Based on diffuse double layer theory, the electrostatic electrification mechanism of metal and nonmetallic pipes is analyzed and compared. The effects of flow regime, pipe properties and oil properties on the oil flow electrification are systematically elucidated. The main forms and hazards of electrostatic discharge of oil pipeline are analyzed in detail. Moreover, a series of electrostatic control and hazard protection measures are put forward from the perspectives of avoiding electrostatic generation and neutralizing static electricity.

The optimal dehydration rate of two cylindrical cyclone separators were compared under the water cut of 95%, 90%, 80% and 70% at the inlet, by changing oil-water mixing flow rate and split ratio. The experimental results show that when the inlet water cut is 95%, 90% and 80%, the optimal dehydration rate of the cylindrical cyclone with orifice vortex finder is 12%~22% higher than the cylindrical cyclone without orifice vortex finder. And the pressure drop between the inlet and the overflow increases 3~52 kPa. When the inlet water cut is 70%, the optimal dehydration rate of the former has little difference with the latter, but the maximum pressure drop between the former and the latter is 68 kPa. Under different experimental conditions, the pressure drop between the inlet and the underflow is not obvious, and the former is slightly higher than the latter. At the same time, when the inlet water cut is constant, the relationship between the optimal split ratio and oil-water mixing flow rate is consistent with the dehydration rate.

In order to analyze the movement rules of bypass pig and the characteristics of piggenerated slug dissipation, a dynamic bypass pigging simulation for a real deepwater gas field was conducted. The movement characteristics of pig velocity and the piggenerated slug dissipation were analyzed through changing the pressure drop coefficient and bypass fraction. The study shows that the pig velocity turns out to be powerlaw distribution with the change of pressure drop coefficients, and within the sensitive range, a small change of the pressure drop coefficient will lead to a huge fluctuation of the pig velocity. The average pig velocity has the tendency of linear reduction with the rise of bypass fraction, the change of which helps to control the pig velocity. By taking advantage of bypass gases to carry and sweep the liquid loading in front of the pig，the running resistance can be reduced, thus the stick phenomena of the pig at the bottom of the riser is avoided. The existence of bypass fraction makes the piggenerated slug dissipate along the pigging period. With the increase of the bypass fraction, the hold up of liquid in the slug is reduced, and the liquid film zone is prolonged, thus making the piggenerated slug volume decrease remarkably. For the optimization of the bypass fraction, an overall consideration should be given to the reasonable scope of pig velocity variations and the piggenerated slug volume, making sure it's within the processing capacity of a slug catcher.

Proppant hydrophobic surface treatment can make proppant reduce oil field produced water while support fracture, control sand. The hydrophobic surface treatment method in terms of both ordinary hydrophobic and superhydrophobic was summed up. The ordinary hydrophobic surface preparation method is divided into three aspects of surface active agent, organic silicon material, fluorinecontaining material; the superhydrophobic surface preparation method is divided into the solgel method, electrospinning method, template method, layers of selfassembly and etching method. Those preparation methods was compared, combined with the situation that water suppression proppant was applied to the field, proposed the hydrophobic surface preparation method was applied to the proppant. Using surfactant hydrophobic modification experiments on quartz surface, the effect of the cationic surfactant CTAB is best, contact angle on the surface of the quartz from 13.7° increases to 73.2°, the Surface tension is 48.88 mN/m, the adsorption capacity of 0.292 mg/g. Finally, it is conceived that hydrophobic surface modification methods was applied to other oilfield areas.

Threshold pressure gradient has an important influence to low permeability reservoir production. According to the site to obtain core laboratory experiments to strike threshold pressure gradient and draw permeability threshold pressure gradient plates. The dynamic simulation mathematical model of reservoir production considering threshold pressure gradient was established. The different threshold pressure gradient on the reservoir production performance was examined under the conditions of formation average permeability and provide guidance onsite low permeability reservoir development.The results show that with the threshold pressure gradient increases,liquid production, the degree of recovery, anhydrous degree of recovery have a decreasing trend and a slight increase in the moisture content. Threshold pressure gradient has an important influence on the balanced injection,the well. Water injection with threshold pressure gradient increases gradually reduced.

Experiments were carried out to investigate the droplet jetting in oil under high voltage AC electric field with different types of white oil and water. With a micro highspeed camera system and image processing technology, the jetting of droplet was observed and analyzed. The results indicate that the droplet jetting is mainly affected by electric field strength, frequency, viscosity and interfacial tension. The critical cone angel of jetting is about 38°, which is only related to dielectric constant of oil and water. When frequency and oil viscosity is increased and interfacial tension is decreased the subdrops departing from mother drop will be smaller and distribute in a smaller angle. As droplet diameter and viscosity increasing, jetting time of small droplets increase. In oil with lower viscosity, the jetting time increase with the decrease of frequency. Jetting quantity of droplet increases with the increase of droplet diameter. 