Study On The Flow Pattern Diversity And Its Influencing Factors In The Two-phase Flow Stage Of Coalbed Methane Migration

The coalbed methane migration exists in the gas-liquid two-phase flow stage,which may have a variety of complex flow patterns.The study on the diversity of gas-liquid two-phase flow pattern in the process of coalbed methane migration and production will help us to better understand the process of coalbed methane production.Based on the crack gas liquid two phase flow visualization of physical simulation,theoretical analysis and field application research on the diversity,the flow pattern in the process of coalbed methane migration output and analyze its influence factor,discusses the cracks in the two phase flow output stage migration mechanism for the formation of the flow pattern of diversity,and the prevention and control mechanism of reservoir slug flow is analyzed.This paper mainly draws the following conclusions:(1)The results of visual physical simulation of the two-phase flow in fractures show that the two-phase flow in fractures has a variety of flow patterns,which can stabilize the flow velocity of liquid and increase the flow velocity of gas,and the flow patterns of bubble flow,air mass flow,stratified flow,wave flow,slug flow,ring flow and mist flow can be formed successively in fractures.The flow characteristics of gas-liquid two-phase flow under different working conditions show that the decrease of liquid flow rate,the increase of crack opening,the decrease of surface tension and the increase of viscosity have inhibitory effects on slug flow.The formation mechanism of each flow state in the process of two-phase flow in fractures is discussed,and the transition mechanism between each flow state and the influence mechanism of each factor on slug flow are analyzed.(2)The water-sensitive damage and quick-sensitive damage of fracturing fluid can greatly reduce the fracture permeability of the reservoir,while the water-locked damage is not conducive to the production of gas and liquid.The decrease of reservoir permeability and the increase of reservoir irreducible water saturation are not conducive to the control of slug flow in the drainage stage.The use of low-damage fracturing fluid can effectively prevent and control reservoir damage.In addition,the fracturing fluid has a low surface tension,which can further inhibit the generation of slug flow.Combined with the flow pattern diversity of the gas-liquid two-phase flow in the fracture,the drainage rate can be controlled reasonably in the drainage process.(3)In the secondary transformation of well sx-01,low-damage fracturing fluid and fracture network transformation were used to maximize the permeability of the reservoir,and continuous,slow and stable drainage was adopted to promote the maintenance of fracture conductivity.According to the data analysis of bottom hole pressure,casing pressure,water yield and gas production at each stage of drainage and mining,the bubble flow,air mass flow,slug flow,ring flow and mist flow which appeared in succession during drainage and mining were analyzed and verified.Although slug flow still appears in the drainage process,considering that there is no pulverized coal production,the slug flow is of low strength,which indicates that the implementation of secondary modification(seam network modification)and the use of low-damage fracturing fluid have an effective inhibitory effect on slug flow.