超深井长裸眼段岩屑运移规律及特征分析

Analysis of Cuttings Transport Law and Characteristics in Long Open Hole Section of Ultra-deep Well

大位移井在深部地层的油气藏开采中得到了广泛应用,但同时面临着井眼清洁不充分、托压、卡钻等一系列问题,为了更好地指导超深大位移井的井眼清洁工作,需要进一步对超深大位移井的长裸眼段的岩屑动态运移特性进行研究。建立了考虑实际井眼轨迹、流体压降及悬浮层颗粒扩散的大位移井两层岩屑运移动态模型。该模型利用有限差分法进行求解,并利用已有文献的实验结果进行验证。对钻井和冲洗两种工况进行模拟研究,认识钻井液排量、钻井液密度、机械钻速、井眼半径等方面对岩屑运移的影响。研究结果表明:在钻井工况下,井斜角越小的井段,岩屑越难以沉积,且钻井液排量越高、钻井液密度越高、井眼尺寸越小、钻速越低,岩屑运移的效率越高;在冲洗工况下,井斜角越小,冲蚀效果越差,且钻井液排量越高、钻井液密度越高、井眼尺寸越小,岩屑运移的效率越高。研究结果对保障超深大位移井良好的井眼清洁具有指导意义。

Extended reach wells have been widely used in oil and gas reservoir exploitation in deep formations.However,a series of downhole problems,such as inefficient hole cleaning,back pressure,and pipe sticking,are also encountered.To better guide hole cleaning,the dynamic characteristics of cuttings transport in long open hole section of ultra-deep extended reach wells must be studied further.According to the law of mass conservation and the momentum theorem,a two-layer dynamic cuttings transport model of extend reach wells was established,considering the actual hole trajectory,fluid pressure drop,and particle diffusion in the suspension layer.The model was solved by the finite difference method and verified by the experimental results in the existing literature.The process of drilling and well washing was simulated and the influence of the drilling fluid flow rates,the drilling fluid density,the rate of penetration(ROP),and the wellbore diameter on cuttings transport were analyzed.Research results demonstrate that,under drilling conditions,cuttings are difficult to deposit in the section with a small inclination angle,the degree of hole cleaning increases with the flow rates and the drilling fluid density,and the smaller wellbore diameter is,the lower the ROP is,which is helpful in hole cleaning.Under well washing conditions,the smaller the inclination angle of the well is,the worse the erosion effect is,and the smaller wellbore diameter is,the higher the efficiency of cuttings transport is,the degree of hole cleaning increases with the flow rates and the drilling fluid density.The research results have a guiding significance for ensuring the good hole cleaning of ultra-deep extended reach wells.