钻完井液静态沉降稳定性评价方法

钻完井液在长期高温静止条件下有可能发生严重沉降，导致下管柱遇阻或开泵困难，增加钻完井作业风险，因此有必要对钻完井液在高温静止下的沉降稳定性进行探讨。国内外学者对钻完井液沉降稳定性进行了广泛研究，目前国内外对钻完井液在高温静止条件下沉降稳定性的评价没有统一的方法。调研了国内外9种方法，综合分析选出了落棒法、沉降因子法、针入式沉实度测定法和静态稳定分层指数法4种方法对水基完井液进行沉降稳定性能评价。实验研究结果表明，静态稳定分层指数所测SSSI值与底部密度相关系数高达0.97以上，能够比较准确地判断完井液沉降稳定性沉降程度；针入式沉实度测定法所测结果只能判定完井液沉降趋势，无法定量评价完井液实际沉降程度；沉降因子法只适合评价分液率较低钻完井液沉降稳定性；落棒法只能粗略判断完井液沉降稳定性。 

Study on the Methods of Evaluating Static Sedimentation Stability of Drill-in Fluids

Serious sedimentation may take place in a drill-in fluid standing for a long period of time at elevated temperatures, resulting in resistance to running tubular goods into the hole or difficulties in starting pump. To resolve this problem, it is necessary to investigate the precipitation stability of a drill-in fluid standing motionless at elevated temperatures. Plenty of studying work has been done by researchers on this issue all over the world, and there is still no standard method for evaluating the sedimentation stability of a drill-in fluid standing motionless at elevated temperatures for a long time. In this study, nine methods used all over the world have been investigated, and four of them, which are falling-rod method, sedimentation coefficient method, penetration degree measurement and static stability stratification index method, were selected for evaluating the sedimentation stability of water base drill-in fluids. Experimental results showed that coefficient of correlation between the SSSI value (measured with the static stability stratification method) and the density of the fluid at the bottom was at least 0.97, indicating that this method is able to be used to predict accurately the sedimentation stability of a completion fluid. The penetration degree measurement method can only be used to predict the sedimentation tendency of a completion fluid, unable to quantitatively evaluate the actual sedimentation degree of the completion fluid. The sedimentation coefficient method is only suitable for evaluating the sedimentation stability of drill-in fluids with low liquid separation rates. The falling-rod method can only be used to roughly predict the sedimentation stability of a drill-in fluid.