| As alternative energy of coal and oil, natural gas has been widely used in industrial production and daily life, and its importance is self-evident. It has become the consensus of all energy companies that increasing natural gas exploration and development, maintaining highly efficient and stable production of the existing gas fields. For a long time, gas well liquid loading caused by the formation water, is the unavoidable problem in the process of gas production. Foam drainage gas recovery technology with its own unique advantages, becomes the first used and the most common measure of drainage and stability production. Howevr, in the implementation process of this technology, there were some undesirable situation such as defoaming poor, a large number of foam accumulated in the separator, foam into the dehydration skid mount and booster compression cylinder leading to the destruction of equipment working condition. These troubles have greatly affected on the applicability and limited its popularization and application. Therefore, in order to ensure the smooth operation of the single well foam drainage technology, and improve the efficiency of defoaming in gathering pipeline, it is necessary that introducing the idea of researching defoaming method based on gas-liquid-foam multiphase flow, and carrying out gas gathering pipeline flow characteristics and defoaming mothed experiments for foam drainage wells, on the premise of lab evaluation and selection of foaming agents and defoamers.By using Ross-Miles method, air flow method, Waring-Blender method for evaluating eight foaming agents and two defoaming agents, one foaming agent and one defoaming agent has been selected in line with test requirements, and testing the properties of foaming and defoaming agents on concentration, temperature, pH, salinity, polymer content. Simulating the gas-liquid-foam flow in single well gathering pipeline and understanding the change of flow pattern under the condition of different factors depended on the foam drainage wells gathering pipeline flow and defoaming simulator. At the same time, measure the pipe-end foam height and pipe flow pressure drop and analyze the correlation between both measured data and the gas-liquid ratio, concentration, temperature or other variables. According to the principle of multiple regression, respective mathematical models were obtained about foam height and pipe flow pressure drop between the various factors, through SPSS’s regression analysis of experimental data. Atomizing nozzle and pipe static mixer were proposed to join in defoamers mixing and filling process, for simulating the working conditions in a variety of defoaming process in the single well gas gathering pipeline. The change of flow pattern, axial distribution of bubble along the pipe and defoaming effect has been observated while injecting defoamers in different ways.The results show that UT-5D foaming agent and FG-2A defoamer can be adapted to the formation conditions of LHS gas-field and conformed to the requirements of the site conditions. In the static evaluation experiments, agent concentration, temperature, salinity had a significant impact on the properties of foam drainage agentsm, while a more stable foaming/defoaming performance in the environment containing acid and alkali or polymers. In the gas-liquid-foam multiphase flow, gas-liquid ratio arranged from 0.55 to 137.42, the multiphase flow showed 4 kinds of flow patterns. They were liquid-foam stratified flow when the gas-liquid ratio α=0.55, gas-foam slug flow when the gas-liquid ratio α=0.978～2.615, gas-foam fluctuation flow when the gas-liquid ratio a=5.69, going into the gas-foam wavy flow when the gas-liquid ratio a≥10.83. Meanwhile, there is a certain correlation between the amount of foam collected at the end of the pipe and pressure drop tested by flowing through the pipeline within a certain time. Namely gas-liquid ratio increasing, pressure drop is decreasing as well as the corresponding amount of foam. By using correlation analysis method to research the relationship among foam height, pressure drop and other experimental factors, it proved that there is a strong correlation between the gas-liquid ratio and foam height or pipe flow pressure drop. Some of the factors which have had a significant impact on the performance of the reagents, such as temperature of the foaming solution, has not the same effect any longer in pipe flow experiment. The traditional straight port injecting defoaming agents, as poor dispersion and poor contact with foam, was difficult to adapt to changing pipe flow state. But atomization nozzle injecting showed a good defoaming effect, especially the small-diameter nozzle that had the characteristics of spray dispersion in small particle size, higher injection pressure at the same flow rate and adapted to the defoaming demand of the dense foam with smaller diameter bubbles. |
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