高压含水气井两相流态节流判断与控制方法

Two-phase flow chokeling results and control in high-pressure gas wells producing water

  • 摘要: 井筒气水两相管流节流前后动态特性分析与控制,对保障致密气等高压含水气井高效稳定安全开采和水合物防治具有重要意义。考虑等熵绝热、等压热容、等容热容、不同井深节流能量等因素,推导气水两相流体流经喷嘴的能量、动能和温度动态变化等热力学微分方程组,建立高压含水气井两相节流能量、节流系统热量、节流物质平衡和流体质量流量变化等井下节流场数学模型,提出一种气水两相井筒节流前后动态特性分析与控制方法,为优化井下节流器及其节流喷嘴的结构参数和保障气井流动安全提供理论依据。最后依据数值模拟手段及其判断结果,以鄂尔多斯盆地东缘大宁−吉县区块为例进行验证,以揭示高压含水气井喷嘴尺寸和深度、含水率、节流前压力和温度对节流前后动态特性的影响规律。结果表明:高压含水气井气水两相流体质量流量先是随节流压力比减小而呈指数级增大,并在压力比降至0.55阈值附近时达到最大值,增大喷嘴下入深度和含水率、同时降低节流前压力和温度,可提高节流后温度,有利于抑制水合物生成;且节流过程临界质量流量受喷嘴内径的影响最大,含水率和节流前压力次之,而节流前温度和喷嘴深度的影响最小,且增加含水率会提高临界质量流量,但产气量也随之下降;大宁–吉县区块现场工程实例分析表明,井下节流喷嘴内径由3.0 mm扩至5.0 mm和节流前压力由14 MPa增至18 MPa时,气水两相流体的临界质量流量提升幅度分别为179.3%和27.8%,而利用地层温度等将节流前温度由313 K升至333 K时,节流过程临界质量流量反而小幅下降且下降幅度仅为5.15%,为此,增大喷嘴内径及其下入深度和节流前压力同时降低节流前温度,有利于提高气水两相流体节流过程中临界质量流量,并提升高压含水气井的产气量。

     

    Abstract: Prediction and control of two-phase flow chokeling in tight gas wellbores are essential for the normal operation and hydrate control of high-pressure gas wells producing water. The thermodynamic differential equations of energy, kinetic energy and temperature and models of chokeling field for two-phase energy, system heat, mass balance and flow were developed under the conditions of isentropic adiabatic, isobaric heat capacity, constant volume heat capacity, and chokeling energy. A methodology on predicting characteristics and control of two-phase flow before and after chokeling was proposed for gas-water two phase flow. It provided a theoretical basis for optimizing the structural parameters of downhole throttle and its nozzle and ensuring the flow safety. The dynamic variations of two-phase flow chokeling with nozzle size and its depth, water content, pressure and temperature were analyzed on numerical simulation and verification of Daning-Jixian oilfield in the eastern margin of Ordos Basin. The results show that the mass flow rate increases exponentially with the decreased pressure ratio, and it reaches the maximum while pressure ratio drops to the threshold of 0.55. The temperature will be enhanced after chokeling and the formation of hydrates will be inhibited while the nozzle depth and water content are increased and pressure and temperature are reduced before chokeling. The effects of nozzle inner diameter, water content, pressure, temperature and nozzle depth on the critical mass flow gradually decreases during chokeling. The increase of water content will enhance the critical mass flow rate and decrease gas production of high-pressure gas wells producing water. The well site analysis on Daning-Jixian oilfield shows that the mass flow rates increase 179.3% and 27.8%, respectively, while nozzle inner diameters enhance from 3.0 mm to 5.0 mm and pressures on chokeling process increase from 14 MPa to 18 MPa. The mass flow rate varies with a small drop of 5.15%. Increasing the nozzle inner diameter, its depth and the pressure while reducing the temperature is beneficial to improve the mass flow rate during the chokeling process of two-phase fluid and increase the gas production in high-pressure gas wellbores producing water.

     

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