Underbalance drilling is a common application in highly fractured and subnormal pressured formation. Technical reasons such as reservoir damage, drilling in depleted zone and hard drilling lead to more economic value in drilling operation. There are several ways to achieve underbalanced well pressure while drilling. One of the most common technique is air, aerated-mud and foam drilling or commonly known as Aerated Drilling.

Drilling with air, aerated-fluid and foam can lead to numerous advantages. In spite of the advantages, it also brings more challenge in design and operation. Cutting transport should be properly calculated to achieve a clean bottom hole condition. Air and gas parameters should be properly designed to prevent Wellbore wash out and formation collapse. All of them should be properly design while maintaining underbalance condition.

In some cases, improper aerated drilling parameters potentially leads to drilling problems such as lost circulation and stuck pipe. This condition should have been mitigated with the proper design of Air, Gas and Foam injection rate. Guo and Ghalambor in 2002 describe main criterion in aerated drilling design. Guo's technique can be applied in air, foam and aerated-liquid drilling. In 2009 Lyons adds more complicated technique, including calculation of liquid hold up and unstable foam drilling. Calculations in this paper are based on both criterion and technique. On operational side, several key takeaways are drawn based on operational challenges in multiple combination of operational conditions. This paper proposes comprehensive techniques to design and parameter in operation in aerated drilling. Several cases are presented in this paper and being evaluated using proposed technique. All of the data are taken from real underbalance drilling parameters in Drilling Operation in Indonesia.

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