ABSTRACT:

Historically, wells in the West Azeri field of the Caspian Sea have been drilled with conventional seawater and gel sweeps. However, the use of a seawater drilling fluid destabilizes the highly reactive formations in surface intervals, resulting in unacceptable movement of the 20-in. surface casing. Surface casings have moved laterally several meters, resulting in casing angles up to 10–15°. Further examination identified mechanical and chemical destabilization of the reactive surface soils as the root causes of the instability. This paper describes the benefits of employing a unique Riserless Mud Recovery (RMR) System with a silicate-based drilling fluid to stabilize the problematic formations, allowing the 20-in. casing to be run and cemented successfully without lateral movement.Laboratory tests identified fluid alternatives that would provide the necessary chemical stability to support the template and casing. Further studies were required to identify the mud weight necessary to provide mechanical integrity to the wellbore. Two field tests were conducted to determine the necessary product formulation to be used with the RMR System. The first test with the RMR System used conventional concentration levels of silicate and KCl in the polymer fluid with an initial mud weight of 1.25 sg. The second test used higher concentrations of silicate and KCl with a higher initial mud weight of 1.45 sg to provide improved wellbore stability

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