Hydraulic modeling and optimization of jet mill bit considering the characteristics of depressurization and cuttings cleaning

A jet mill bit(JMB)is proposed to increase the drilling efficiency and safety of horizontal wells,which has the hydraulic characteristics of depressurization and cuttings cleaning.This paper fills the gap in the hydraulic study of the JMB by focusing on the hydraulic modeling and optimization of the JMB and considering these two hydraulic characteristics.First,the hydraulic depressurization model and the hydraulic cuttings cleaning model of the JMB are developed respectively.In the models,the pressure ratio and efficiency are chosen as the evaluation parameters of the depressurization capacity of the JMB,and the jet hydraulic power and jet impact force are chosen as the evaluation parameters of cuttings cleaning capacity of the JMB.Second,based on the hydraulic models,the effects of model parameters[friction loss coefficient,target inclination angle,rate of penetration(ROP),flow ratio,and well depth]on the hydraulic performance of the JMB are investigated.The results show that an increase in the friction loss coefficient and target inclination angle cause a significant reduction in the hydraulic depressurization capacity,and the effect of ROP is negligible.The flow ratio is positively related to the hydraulic cuttings cleaning capacity,and the well depth determines the maximum hydraulic cuttings cleaning capacity.Finally,by combining the hydraulic depressurization model and hydraulic cuttings cleaning model,an optimization method of JMB hydraulics is proposed to simultaneously maximize the jet depressurization capacity and the cuttings cleaning capacity.According to the drilling parameters given,the optimal values of the drilling fluid flow rate,backward nozzle diameter,forward nozzle diameter,and throat diameter can be determined.Moreover,a case study is conducted to verify the effectiveness of the optimization method.

Numerical and experimental investigation on the depressurization capacity of a new type of depressure-dominated jet mill bit

Efficient cuttings transport and improving rate of penetration(ROP)are two major challenges in horizontal drilling and extended reach drilling.A type of jet mill bit(JMB)may provide an opportunity to catch the two birds with one stone:not only enhancing cuttings transport efficiency but also improving ROP by depressuring at the bottom hole.In this paper,the JMB is further improved and a new type of depressure-dominated JMB is presented;meanwhile,the depressurization capacity of the depressure-dominated JMB is investigated by numerical simulation and experiment.The numerical study shows that low flow-rate ratio helps to enhance the depressurization capacity of the depressure-dominated JMB;for both depressurization and bottom hole cleaning concern,the flow-rate ratio is suggested to be set at approximately 1:1.With all other parameter values being constant,lower dimensionless nozzle-to-throat-area ratio may result in higher depressurization capacity and better bottom hole cleaning,and the optimal dimensionless nozzle-to-throat-area ratio is at approximately0.15.Experiments also indicate that reducing the dimensionless flow-rate ratio may help to increase the depressurization capacity of the depressure-dominated JMB.This work provides drilling engineers with a promising tool to improve ROP.

射流磨钻头流场特性及其外排屑槽影响的数值模拟

在油气田开发中,水平井钻进时携岩困难、托压严重、机械钻速慢等问题严重影响生产效益。射流磨钻头既能降低井底压差实现欠平衡提速,又能粉碎岩屑实现岩屑悬浮运移,为水平井安全高效钻井作业提供技术支撑。研究基于计算流体力学方法,建立了射流磨钻头流场的数值仿真,并采用标准k-ε双方程模型对其流场特性及其外排屑槽尺寸的影响进行了模拟研究。结果表明,无外排屑槽时射流磨钻头的降压效果最好,井底低压区和中压区呈现一降一升的趋势;井底压力沿钻头直径方向分布极不均匀,高压与低压交错出现;在开外部排屑槽的情况下,内排屑孔的总体积流量占比达100%以上,随单个外排屑槽宽度的增大,内排屑孔的总体积流量占比增加,且外排屑槽存在钻井液回流的现象,回流体积流量占比4%以内。研究结果为射流磨钻头的优化设计与应用提供理论依据。