Difference Between Overbalanced and Underbalanced Drilling?

 

Difference Between Overbalanced and Underbalanced Drilling?

Drilling operations are fully one of the most important stages in the exploration and development of oil and gas fields. Among the numerous categories of drilling methods, two are distinguished overbalanced and underbalanced drilling. The two techniques do have specific strengths and weaknesses that alter performance issues like wellbore stability, reservoir deliverability, and safety. Now let this article discuss the details of how and when each of these techniques is used and differs from the others.

Overbalanced Drilling

The overbalanced drilling is also conventional where the pressure from drilling fluid is greater than formation pressure, that is pressure within the formation being drilled. This surface pressure essentials adverse pressure differentials to prevent the formation of fluids including oil, gas, or water from invading the wellbore during drilling operations. Overbalanced drilling restores the well control by using the mud column to prevent the intrusion of reservoir fluids and stabilize the wellbore from below thereby reducing the incidence of blowouts from the subsurface.

Key characteristics of overbalanced drilling include: Key characteristics of overbalanced drilling include:

Pressure Differential: 

This kind of pressure is greater than the formation pressure, and as such, there is a positive pressure differential exerted by the drilling fluid.

Wellbore Stability: 

Overbalanced drilling controls the formation entry of fluid so that it assists in controlling temperatures, pressures, and other factors aside from formation that otherwise would cause well-bore formation instability and damage.

Formation Evaluation: 

Overbalance drilling controls well and effectively but does not allow a proper assessment of formation characteristics and the productivity of the reservoir in contact with the fluids in it.

Underbalanced Drilling:

On the other hand, underbalanced drilling was where the pressure within the wellbore is less than the formation pressure of the rock being drilled. This enables the reservoir fluids to enter into the well bore for better well bore cleaner and enhanced productivity of the reservoir. Underbalanced drilling is mainly used in low permeability or formations that have a fragile structure because formation damage is something that needs to be avoided.

Pressure Differential: 

That is why formation pressure is maintained to be always higher than pressure within a well bore in order to enable the flow of reservoir fluids to the well bore.