基于射线技术的低压竖直管气液两相流模型研究

Investigation of Low-pressure Vertical Gas liquid Flow Measurement Based on Gamma Technology

为解决油田开采末期因地层压力下降引起的含气率增加、气液速度差异变大而导致的气液两相流测量困难,本文采用文丘里管和射线传感器相结合的方法对竖直管自下而上流动方向的气液两相流进行了试验研究。其中射线传感器布置在文丘里的喉部,用于测量空隙率,而文丘里管用于测量两相流总流量。从均相流模型出发,结合Chisholm滑速比经验公式,提出了一种新的液相修正系数与空隙率的关联式。试验工质采用来自大庆油田产出的天然气、原油及地层水,试验压力为0.1~0.4 MPa,空隙率范围为34.5%~95.8%。根据试验结果,利用本文计算模型得到的液流量、气流量及气液总流量的均方根误差分别为3.4%、9.6%和3.2%。与利用滑速比计算液相修正系数的Zhang模型进行对比,本文的模型计算得到气量结果明显更优,表明空隙率可以更好地表征低压力下气体流量变化,为工业应用提供一种新的计算思路。

As results of the downhole pressure decreasing during the life cycle of production wells,the gas volume fraction of wells increases and have a wide range especially under low pressure conditions.Furthermore,obvious gas-liquid slip adds the difficulty of gas-liquid two phase measurements.In order to solve this problem,a measuring system combining Venturi and gamma sensor was applied to measure vertical upward gas-liquid flow.Gamma sensor was installed at the throat of Venturi for void fraction measurement.To simulate the true fluids of wells,natural gas,produced water and crude oil from Daqing oil field were used as the test medium and test pressure ranging from 0.1 to 0.4 MPa.The void fraction ranged from 34.5% to 95.8%.A new correlation between liquid phase coeficient and void fraction was proposed based on experiments and flow pattern analysis.The single phase flow and gas-liquid two phase flow were calculated accordingly with considering slip ratio correlation.The root mean square error(RMSE) of the liquid flow,gas flow and gas-liquid two phase flow are 3.4%,9.6% and 3.2% respectively.Zhang model was modified based on the experiments and the RMSE of the liquid flow,gas flow and gas-liquid two phase flow are 3.2%,20.2% and 2.9% respectively.The gas flow measurement of new correlation is much better than Zhang model.It shows that the correlation deriving from void fraction can represent the gas flow change of low pressure and provides a valid method for industrial application.