Planning UBD in Horizontal Well to Minimize Formation Damage

International Association of Drilling contractors (IADC) has defined underbalanced drilling (UBD) as a technique in which equivalent circulation density (ECD) of drilling fluid is intentionally maintained less than effective formation rock pressure (Pf) in openhole section at any depth. That results in tendency of fluid to inflow from formation into wellbore.

UBDtechnique has grown rapidly as alternative technique to conventional drilling(overbalanced) to eliminate or significantly reduce the problem of formation damage in horizontal well. However, Bennion and Thomas  have stated the possibility of existing formation damage in condition where original saturation of hydrocarbon or water in the reservoir is lower than irreducible saturation of the phase that used in drilling. This lead to spontaneous imbibition is caused by capillary pressure and wettability properties. This generally appears in low permeability gas reservoir which has very low initial water saturation. Read more....................