Summary

According to the drilling program approved for Hai Thach field, the drilling section below the 16” casing liner (14.85” internal diameter) will be carried out by two separate BHAs: first drilling the 12.25” section by PDC bit to the section target, then under-reaming the wellbore to 14.5” and 16.5” diameter in order to run 13.625” casing string. Using two separate BHAs for reaming the wellbore certainly leads to a time increase in the run in hole (RIH) and pull out of the hole (POOH) of the drill-string and hence the associated costs such as rig and other related third party services. Therefore, it is necessary to study and calculate the optimal drill-string design to ensure the wellbore under-reaming as well as to minimise the drill-string running time, thereby improving the Drillex and Capex. The application of the optimised reamer string design in the wells of Hai Thach field has brought a feasible concept that can be applied for other wells having similar profiles and geological stratigraphy in Vietnam in the future.

Key words: Under-reamer string optimisation, wellbore reaming, drill-string simulation, reamer string design, Hai Thach field.

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