Study On The Experiment And Model Of Drainage By Speed

For the problem of liquid loading existing in the middle and later yielding periods of the low pressure, low porous, low yielding and water-bearing gas reservoir, gas drainage technologies are urgently needed to maintain wells production stably. Velocity string drainage gas recovery can reduce critical gas flow velocity of wellbore, decrease the loss of the slippage between gas and liquid, and improve the ability of gas well carrying liquid. Because of this technology with simple construction, lower one-time investment, no killing well construction, little damage for formation and other advantages, its application becomes more and more widely. Nevertheless, Daniudi gas field production practice has shown that gas production, fluid production and oil pressure of some gas wells declined obviously after using velocity string. The reason is that with no clear understanding of gas-liquid two-phase pipe flow regularity and the mechanism of liquid carrying of velocity string, the selection of speed pipe wellbore pressure drop prediction model and the continuous liquid carrying critical gas flow model are not accurate, which leads to irrational choice the diameter of velocity string, eventually leads to gas production capacity decreasing. Therefore, this article carried out two-phase flow velocity pipe pressure drop experiments and continuous liquid carrying experiments. Based on experimental data, the pressure drop formula and the continuous gas flow formula of velocity string are established. The main study contents completed are as follows:(1) According to the commonly used production string size of Daniudi velocity string drainage and gas recovery (φ38.1,φ50.8mm, annulus φ38mm+φ76mm), three diameter strings are chosen (φ40mm,φ50mm, annulus φ40mm+φ80mm) to design physics simulation devices of velocity string drainage and gas recovery. The total length of experimental pipeline is8m and the angle changes from0°to90°. It can be used to simulate gas-liquid two phase flow at different segments of the velocity string drainage and gas wells.(2) Conducting gas-liquid two phase flow experiment of the40,50mm diameters of tube and small annular, internal relationship between flow pattern and pressure drop is analyzed. Meanwhile, measured pressure drop of velocity string and small annulus at different condition of gas rates (1～10m3/d), liquid rates (2-34m/s) and inclination (15°～77°), then analyzing these three factors influence on pressure drop. Results of experiment provide data support for establishing pressure drop model of velocity string.(3) Based on experimental data at the low fluid rates (1～10m3/d), this article modifies the Hagedorn&Brown model, then deduces pressure drop model which is suitable for gas-water two-phase flow regularity of velocity pipe. Using34groups of flowing pressure test data of velocity strings belong to Daniudi drainage and gas recovery wells, this article evaluates eight pressure models, including the Hagedorn&Brown modification model. The evaluation results indicate that the error of correction model is minimum, which provides a pressure drop method for gas wells of Daniudi gas field. (4) Carrying out continuous liquid carrying experiments of velocity strings and small annular, testing critical gas flow rate at different liquid flow rates, inclination and diameters, analyzing these three factors how to influence continuous liquid carrying critical gas flow rate. At the same time, using digital camera to capture the flow pattern under the condition of continuous liquid carrying, which revealed the existing condition of flow pattern when continuous liquid carrying happens.(5) Based on the experimental data, considering the impact of fluid rate, inclination and diameter, this article modifies the correlation coefficient of the Belfroid model, establishes a comprehensive liquid carrying modified model. And verifying the model by18gas wells test data in Daniudi gas field, the accuracy is88.9%.The pressure drop model established and the continuous critical gas velocity model established provide a method for parameter optimization design and liquid carrying dynamic prediction of velocity string drainage and gas recovery.