Modelling the hydraulic lift phenomenon during casing while drilling

Abstract

Casing while Drilling (CwD) is a process in which a well is drilled and cased simultaneously. This innovative technology has been successfully practiced for the past decade. However, narrow annuli often causes problems like packing or caving in the wellbore that may restrict the fluid flow and hole cleaning capacity. Hydraulic lift could be one of the beneficial factors that can be used to increase the efficiency of drilling as it can be used to monitor the wellbore condition. The purpose of this project work is to develop a theoretical model to calculate the overall hydraulic lift during CwD to evaluate the wellbore irregularities. As CwD process utilizes large diameter casing to drill, several forces act upwards on the casing. Usually Small annulus brings about higher frictional pressure drop compare to the conventional operation that causes high upward drag force on casing wall. Another force acts upwards at the bottom face of the casing while fluid exits through the nozzles. In this study fluid hydraulic principles have been used to generate the overall hydraulic lift model. This theoretical model has then been compared with field measurement from hookload. Deviation of the field measured value from the predicted hydraulic lift is an indicator of wellbore conditions. In this study trend of hydraulic lift predicted using theoretical model is compared with the field measured value of an well. Observation of this comparison is then analyzed with the field report to validate the model. Hydraulic lifts for three different depth interval and flow rates are measured. Findings of the comparisons are correlated with the summary of the field report for each section. Most significant finding is higher field measured hydraulic lift means higher friction due to packing or caving from the well bore that resembles the field observation also for a certain interval. The novelty of using hydraulic lift in CwD will enable the monitoring of wellbore condition to improve hole cleaning efficiency during operation.