筛管砾石充填井筒附近压降计算方法

认识到套管射孔砾石充填井井筒附近压降发生在 3个流动区域内 ,近井地带向射孔炮眼的汇聚流动区域 ,炮眼内砾石层的线性流动区域以及筛套环空砾石层中的发散流动区域 .以 Bernoulli压降方程为基础导出了计算向炮眼的汇聚流产生的压降的新方法 .以 Forchheimer方程为基础导出了筛套环空锥形发散流的压降简化计算公式 .结果表明 :井筒附近压降主要发生在汇聚流区域和炮眼内砾石层 ,而环空砾石层的压降相对较小 ;射孔参数及砾石渗透率是影响砾石充填井井筒附近压降的主要因素 ,砾石充填井应采用孔径大于 1 5 mm,孔密 30孔 / m左右的参数射孔 ,砾石层渗透率至少应保持在 30～ 40 μm2以上 .

A New Calculation Method of the Pressure Drop Around the Wellbore of a Gravel-packed Perforated Well

The pressure drop around the hole of a gravel packed perforated well takes place in following three areas: the convergent flow area from near well zone to a perforation channel, the linear flow area inside a perforation channel, and the divergent flow area between casing and screen tube. In this paper, the new model of calculating the pressure drop in the convergent flow area is derived on the basis of Bernoulli equation, and the simplified formula of calculating the pressure drop in the divergent flow area is also presented based on Forchheimer equation. The results of several cases show that the main part of the pressure drop takes place in the convergent flow area and the linear flow area, and the pressure drop in the divergent flow area is very little. The results also show that perforating parameters and the permeability of packed gravel are the key factors of affecting the pressure drop. The diameter of perforation channels had better be more than 15mm, and perforation density should be above 30 holes per meter. For high productivity, the permeability of packed gravel should be 30~40 Darcy at least.