Optimization research and application of polymer drilling fluid in shallow extended reach wells in the eastern South China Sea
Enping Oilfield is located in the eastern South China Sea,where shallow extended reach wells encounter loosely cemented formations with high mudstone content,prone to easy hydration,dispersion,and slurry formation.During the drilling process,challenges arise,including drilling fluid thickening,wellbore instability,induced well leakage due to an increase in circulating equivalent density,and high friction torque.A careful selection of additives are made to address these challenges,including the low molecular weight amide-based polymer PF-BIOCAP,amine-based polymer PF-UHIB,and borate ester compound vegetable oil PF-EXLUBE,aimed at improving the inhibitive and lubricating properties of polymer drilling fluid.Evaluation results demonstrate that the mudstone rolling recovery rate of the drilling fluid reaches 96%.After contamination by mudstone cuttings with mass fraction of 15%,the apparent viscosity increase rate has significantly decreased.Moreover,both the friction coefficient and mudcake viscosity coefficient are maintained below 0.1,which show excellent inhibitive and lubricating properties.The rheological performance meets the requirements for wellbore cleanliness.This polymer drilling fluid system has shown significant success in shallow extended reach wells in Enping Oilfield,effectively addressing technical challenges such as mudstone wellbore instability,mudstone cuttings hydration and slurry formation,and high friction torque.Its successful application in shallow offshore extended reach wells holds valuable guidance for widespread adoption.
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