酸性天然气侵入井筒多相流动规律研究

Research on the Principles of Wellbore Multiphase Flow During Sour Gas Influx

在综合应用井筒两相流压降和传热模型的基础上,考虑地层渗流与井筒耦合,考虑了钻井液和侵入酸性流体的基本物性参数与井筒温度压力的耦合作用,酸性天然气与水基钻井液间的相互作用(化学反应和溶解),建立酸性天然气侵入井筒多相流计算模型。通过数值计算分析,钻遇相同地层条件下,不同组分(甲烷+二氧化碳,甲烷+硫化氢)两类酸性天然气藏的环空压力等变化规律。结果表明,酸性天然气与水基钻井液化学反应消耗酸性天然气质量流量很小,可忽略。而井筒内溶解度较大,酸性天然气在近井口处由于溶解度迅速降低,气体密度发生突变,且二氧化碳和硫化氢摩尔分数的越大,突变位置越靠近井口处。酸性天然气中二氧化碳和硫化氢摩尔分数越大,井底压力变化越小,不能根据井底压力下降值直接判断溢流程度。

The mathematics model of wellbore multiphase flow after sour gas influx is established.The paper is comprehensively based on the application of pressure drop model and heat transfer model for two phases flow in wellbore,coupling the wellbore unsteady flow and formation seepage,and the mutual reaction(chemical reaction and solubility) between sour gas and water-based drilling fluid into consideration.The pressure distribution in wellbore is calculated by numerical method with different components(methane+carbon dioxide,methane+hydrogen sulfide) when drilling the same formation.The results indicates that the chemical reaction can be ignored.The solubility of carbon dioxide or hydrogen sulfide in the water-based drilling fluid is very remarkable.When the sour gas is near the wellhead,the solubility is decreased sharply.The density of sour gas has a sharp change near the wellhead.The higher he mole fraction of carbon dioxide and hydrogen sulfide of sour gas is,the shorter of distance near the wellhead is.The higher he mole fraction of carbon dioxide and hydrogen sulfide of sour gas is,the smaller change of pressure in the bottom hole pressure is.So that we shouldn't judge the overflow lever according to the drop of bottom hole pressure.