A Quantitative Investigation of the Laminar-to-Turbulent Transition: Application to Efficient Mud Cleaning

摘要

Spacer and wash fluids play an essential role in the cementingof oil and gas wells. They are pumped ahead of the cement tooptimize the mud displacement, enable a proper hole cleaning,and obtain a good cement bond at the formation and the casingsurfaces.The design of spacer fluids relies on an ensemble ofphysical and chemical characteristics of the spacer includingflow characteristics (rheological properties), the stability of theweighted spacer suspension, and the compatibility with otherwellbore fluids.The flow characteristics of spacer fluids are the key tosuccessful cementing. The wellbore fluids pumped in the fieldusually behave as viscoplastic fluids. The non-Newtoniannature of these fluids must be accurately modeled whendetermining the flow behavior around a centered or eccentricannulus to accurately determine flow regime and dynamicpressures in the annulus along the entire column of fluid.Turbulent flow is the preferred flow regime for efficientmud removal in the annulus, provided the cleaning fluid iseffectively in turbulent flow all around the eccentered annulus.Therefore, a reliable criterion for the critical Reynolds numberis needed to properly design the well-cleaning process anddetermine whether it is feasible to be in turbulent flow.In an effort to better understand the fluid dynamicsinvolved with mud cleaning, we have conducted anexperimental study on a series of spacer and model fluids.Axial velocity and relative fluctuation intensity measurementswere conducted using three different techniques: (1) ultrasonicDoppler technique, (2) hot film anemometry, and (3) laserDoppler velocimetry. On the basis of these results, we havebeen able to fully characterize the laminar-to-turbulenttransition and evaluate the pressure drop caused by highlynon-Newtonian fluid. The results of this study help us definemore reliable estimates of the minimum pump rate that willlead to substantial well-cleaning efficiency, taking intoaccount the rheological behavior of non-Newtonian fluids.