气井井流动能分析及考虑动能项的井底流压计算方法

ANALYSIS OF KINETIC ENERGY IN GAS WELL AND A BOTTOM-HOLE FLOWING PRESSURE CALCULATING METHOD CONSIDERING KINETIC ENERGY TERM

在采气工艺中 ,利用井口压力计算井底压力及井筒压力分布是一项常用计算。进行这项计算的实用公式都是从气体稳定流动能量方程入手 ,经过一定的假设、简化推导而得的 ,其中的一项假设即是将总能耗之一的动能项忽略不计。然而 ,误差分析表明 ,此项假设仅适用于某些生产条件 ,如动能损失在总能耗中所占份额较小、测压仪表精度低等等。文章从气体稳定流动能量方程出发 ,首先推导并定义了动能因子 (C) ,即动能损失占总能量损失的分数 ,其大小主要取决于油管直径、流量和计算管段上的平均压力。然后利用推导出的动能因子的实用公式 ,结合川东地区情况 ,分别对 5 0 .8、6 3 .5、76 .2mm油管 ,利用实用公式计算了气井产量在 (10 6 0 )× 10 4 m3/d、井口流压在 2 30MPa范围内取不同值时动能因子的数值。根据计算结果 ,从工程观点出发 ,选取C <10 -3 作为一判别值 ,认为只要C <10 -3 ,则利用井口流压计算井底压力时动能项就可以忽略 ,否则应该予以考虑。最后文中给出了考虑动能项的井底压力计算实用公式。

In gas production technology,it is a general task to calculate bottom-hole pressure and determine wellbore pressure distribution by use of wellhead pressure.All the formulae applied to make such a calculation were derived from the energy equation of gas steady flow through a certain assumption and simplification,in which the kinetic energy,part of the total energy consumption,was neglected.Error analysis,however,indicates that this assumption is only suitable for those production conditions,as a small share occupied by kinetic energy loss in the total energy consumption and low pressure gauge accuracy,etc.In light of the energy equation of gas steady flow,the kinetic energy factor (C),i.e.kinetic energy loss-to-total energy consumption ratio,is derived and defined first,which magnitude is dependent upon tubing diameter,flow rate and the average pressure on pipeline section calculated.Then,in combination with the practical data collected from East Sichuan,the values of the kinetic energy factor were calculated for the tubing diameters of 50.8,63.5 and 76.2mm at different gas well yields ranging from 10×10 4m 3/d to 60×10 4m 3/d and at different wellhead flowing pressures ranging from 2 MPa to 30MPa by applying the derived practical formula considering the kinetic energy factor.According to the results calculated,C<10 -3 is taken as a discriminant value from engineering viewpoint.It is thought that when bottom-hole pressure is calculated by use of wellhead flowing pressure,the kinetic energy term may be neglected as long as C<10 -3 ,otherwise it should be considered.Finally,a practical formula taking account of the kinetic energy term is proposed for calculating bottom-hole pressure in the paper.