| As a kind of efficient drainage gas production technology,the velocity string can get better drainage gas production effect without changing the production system,and it is one of the most competitive technologies for increasing production of water-bearing gas reservoirs because of its simple process and low operation cost.The velocity string simulation technology of foreign oil companies is relatively mature,but its intellectual property rights are protected,so it is necessary to conduct independent velocity string drainage gas flow model analysis and algorithm research.In this paper,through reasonable model selection and establishment,the algorithm architecture design is carried out to realize the development of velocity string module,and to provide technical support for long-term and efficient production of velocity string operation.The main research work of this paper includes:(1)The fluid flow model analysis of velocity string was carried out.Based on the physical properties of natural gas Wells,the gas-liquid multiphase flow analysis was carried out considering the influence of gas-liquid and gas-liquid parameters on the mixed gas-liquid two-phase parameters.Based on the mechanism of wellbore fluid accumulation,the method of diagnosis and calculation of fluid accumulation height is put forward.Based on the droplet and liquid film theory and considering the fluid-gas-liquid ratio,the critical fluid carrying flow rate model of gas carrying liquid out of well was established.According to the flow field and structure characteristics of the velocity string,the elongation and pressure drop in the pipe are studied,and the pressure drop model of the flow passage is established.(2)The research on drainage gas recovery algorithm of velocity string was carried out.According to the analysis of multiphase flow and the study of flow passage pressure drop,the calculation model of velocity string is simplified reasonably.The calculation objective of production factors of velocity string(dynamic analysis of reservoir inflow and wellbore outflow)was analyzed,and the node method was adopted to solve the problem in sections.The multi-phase flow algorithm of velocity string was solved and the architecture was designed.The calculation data of the model established in this paper is consistent with the trend of the data collected from the field operation well,and the overall error is within the scope of the engineering permission,which meets the needs of the field use.(3)The operation parameter analysis of drainage gas recovery with velocity string was carried out.Based on the algorithm model of velocity string drainage and gas recovery,the relationship between nitrogen flow rate,wellhead pressure range and liquid lifting flow rate is studied for velocity string drainage operation,and the reasonable parameters of efficient drainage can be determined.Considering the relationship between different pipe diameters and the flow rate at the bottom of the pipe and the friction in the pipe,the production characteristic curve is analyzed,and the reasonable pipe diameters at the critical liquid carrying flow rate are obtained.Combined with the numerical analysis of the algorithm module and CFD simulation analysis,the relationship between the structural parameters(wall thickness,taper)and the running depth of the coiled tubing and the carrying capacity is analyzed.It can be seen that choosing the coiled tubing with small taper and large wall thickness difference,and installing it to the middle and deep position of the producing zone,will help to improve the lifting force of carrying liquid.(4)The velocity string algorithm module was developed.Based on the established fluid flow model,algorithm architecture design and parameter analysis,comprehensive consideration of input,judgment,output conditions,using C# language compilation.This module can realize graphic visualization analysis and provide scientific technical support for field drainage gas production of velocity string. |
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