The development of heavy oil fields imposes several challenges for well construction: in order to guarantee minimum flow rates, long horizontals intervals are often required. Long horizontals are associated to long reservoir exposure times which can affect final open hole quality. Rock fluid interaction issues and BHA design directly affect the drilling of sensitive formations, such as non consolidated heavy oil reservoirs.

This article presents initially a comprehensive data analysis of caliper logs in offshore heavy oil wells drilled in Brazil. The analysis correlates hole enlargement with relevant parameters such as fluid type, flow regime and BHA composition. Data sources considered were real time monitoring equipment, logging data and drilling reports. Results indicate that water based fluids and turbulence proved to stimulate hole enlargement and should be avoided.

The study is also supported by a unique experimental work where fluid flow conditions were simulated in a pilot unit where the wellbore was represented by a non consolidated synthetic core saturated with high viscosity oil. For a given flow rate, hole enlargement is monitored with time by a real time CT scanning technique. Experimental results are in agreement with field observations. The role of drillstring composition was not contemplated in the experimental study.

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