Publications

Underbalanced drilling (UBD) can be defined as “drilling into a formation in which formation pressure, or pore pressure, is greater than the pressure in the wellbore. Underbalanced drilling is used to avoid and limit the lost circulation problem and as a method of preventing formation damage and differential sticking while increasing the drilling rate.Types of fluid commonly used in underbalanced drilling include dry air, natural gas, mist, foam, gasified water or oil, nitrogen, or any other drilling fluid that can ensure wellbore hydrostatic pressure stays lower than formation pressure. Reduced pressure drilling systems provide fluid densities ranging from near zero to approximately 7ppg.One of the problems often encountered in field X is clay swelling, as claystones and shales are present in many layers. Swelling resulting from claystone and shale can lead to borehole instability, and shale can manifest abnormal pressures. Another problem occurring in this field is the reality that the field has entered its depleted phase, a condition leading to lost circulation problems in this reservoir in any subsequent next drilling.This paper will discuss the feasibility of optimizing the underbalanced drilling fluid to be used in this field. Swelling and lost circulation problems will be the main issues to be discussed in this paper because of the large volume of claystone and shale found in this field.Keywords: Underbalanced drilling fluid, Swelling, Lost circulation