The viscosity of heavy oil is high, the pipeline transportation is difficult, and the viscosity decreases greatly after dissolved gas. Thus researching viscosity-reducing properties of dispersion system of heavy oil with dissolved gas is of great significance to the actual pipeline operation. The viscosity-reducing mechanisms, viscosity models and influence factors of heavy oil with dissolved gas are summarized. The research indicates that dilution micelle damage, swelling, molecular force and micro-bubbles effect can reduce the viscosity of dispersion system. Viscosity models are mainly established by Shu, Abivin and so on, and the defects in the model are presented. The property of oil and gas, temperature, pressure, the amount of dissolved gas and micro-bubbles have different effects on the system's viscosity, and the direction of the heavy oil with dissolved gas is proposed.

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.

In order to better guide the cyclone design and optimization, the theoretical basis, applicability and accuracy of the prediction models of cyclone performance were investigated. Research progress on the prediction models of separation performance and pressure drop was reviewed. Combined with the influence of the particle load, particle size distribution, particle collision and coalescence, high temperature, high pressure, structure and parameters on the separation performance, the prediction models were compared and analyzed from aspects of the theoretical basis, modeling ideas and modeling tools. The results showed that prediction models were gradually rationalized but still limited. Based on the current conditions of research and application, the future direction for development of the prediction models was prospected. Comprehensive analysis of various factors' effects on the prediction models and the extension of the gassolid separation theory and prediction models to the gas-liquid separation field might be the focus of the further research．

        Since the decline in conventional oil production, the research and development of unconventional oil are very important. Tight oil has the following characteristics. First, the property of different layers of tight oil is different, and the second is the amount of fluid in the production cycle is variational. To determine the tight oil gathering and transportation scheme, the entire production cycle is divided into three stages. The two schemes of heating and water injection are analyzed by simulating and comparing their Gathering safe distance and energy-consumption. The results show that water injection is better than heat gathering and transportation technology in these two aspects. So as to ensure the normal operation of gathering system and save operating costs, we choose water injection gathering and transportation technology.