UNDERBALANCE vs OVERBALANCE
Generally there are 4 (four) types of drilling fluid, which are grouped into types "overbalance" that are (1) Conventional Drilling Fluid (2) Non Damaging Drilling Fluid and the "underbalance" that are (3) Aerated Drilling Fluid and (4) Underbalance Drilling (UBD).
In terms of preserving the integrity of the formation of damage against invasion of drilling fluid / solid / filtrate that is teoritically underbalance drilling has the advantage compared to overbalance drilling the first commonly used in drilling techniques.
However, in practice underbalance drilling technique has many constraints, especially in operation and are not able to make underbalance conditions at any point so that the problem of invasion into the drilling fluid / filtrate / solid remains will take place on the drilling of this type. So that this condition will not be separated from the problem of formation damage and hole instability in addition to the very expensivecost for the use of UBD.
Use of Non-Damaging Fluid Drilling will be easier to implement operationally as the use of conventional drilling fluid commonly used in overbalance condition. However, Non-Damaging Fluid Drilling holes will not be cause hole instability unlike in conventional drilling fluid that would cause many problems such as caving / swelling that overall costs would swell the cost of other services.