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D-Field is a mature field in Sumatra that utilizes steam technology to enhance oil production. A huge amount of oil has been produced since the application of this technology in the early 1980’s. As production keeps declining, the idea came to produce the oil from the new lower formation of an existing well called deepening.

Well deepening is an effort of drilling a formation below original well depth. Well deepening job is supposed to be done by drilling rig due to its complexity such as managing wellbore stability, managing loss circulation, solid control requirement and drilling fluid handling.

However, utilizing drilling rig is considerably uneconomic due to high cost and expected low oil gain from mature oil field. Additionally, drilling rigs availability are limited and require additional well pad construction to accommodate drilling rigs.

This paper discusses the strategy of utilizing workover rigs in well deepening operations as the preferred alternative than drilling rig. Due to limited capability of workover rig, it requires several operational adjustments such as circulation rates, rate of penetration (ROP), and torque management. Hydraulic simulation and drill string design were exercised to ensure the job objectives are achieved. Risk assessments were also conducted to mitigate associated risks are mitigated.

Having implemented the robust planning, the team successfully completed 21 well deepening jobs in 2024 with approximately 50% cost compared to utilizing drilling rigs. The new practices has become new standard of well deepening jobs in D-field. In 2025, approximately 20 jobs will be executed with this technique.