For drilling in different areas with different geological structure, the capabilities of drilling methods should be examined. Studies show that most of Iran’s oil reservoirs are tougher in comparison to many countries and the formations have many cracks. For this reason, due to the lost circulation of mud in these cracks, there is always the risk of financial cost and damages.

The main priority in drilling such formations is the use of Under Balanced Drilling (UBD) method. Also in resources that are sensitive to the penetration of fluids and solids and UBD method should be used. In formations with shale fracture cracks, due to high mud lost circulation, the use of conventional drilling methods causes lots of damage in drilling operations. In these cases, the best type of drilling is to use UBD drilling with fluids such as foam. High drilling speed is an influential factor in drilling operations in these areas. However, in formations which the well wall has low strength and stability (increasing the probability of well collapse) as well as formations that swell and reduce the diameter of the well or watery formations, UBD drilling is not recommended.

Introduction to drilling methods