| Underbalanced Drilling (UBD) is not a new concept but its utilization has started within the last few years. It has now emerged as a first, thought drilling in the regions with complex, lower quality reservoirs or existing depleted fields. Applications of Underbalanced Drilling (UBD) technologies have reached significant levels of acceptance throughout the world.;The purpose of this report is to critically review the operation of underbalanced drilling with coiled tubing. This report deals with the details of CT drilling equipment and underbalanced drilling. It also deals with the related problems and solutions that can occur during UBD, drilling fluid requirements and completion processes of underbalanced drilling.;Underbalanced drilling is defined as drilling while keeping hydrostatic pressure at the drill bit less than the pore pressure of the formation being drilled. Underbalanced drilling offers many advantages including reducing formation damage, increasing the rate of penetration (ROP) and bit life, reducing the number of trips into the hole, minimizing differential sticking of pipe, etc. Underbalanced Drilling with Coiled Tubing is a concept in which coiled tubing is used instead of conventional drill pipes. This helps in maintaining the Bottom Hole Pressure (BHP) below the formation pressure without any interruption as compared to the conventional drilling pipe where there is a chance of loss of pressure control while changing the pipes. With coiled tubing there is no need to change pipes; therefore it helps in maintaining the BHP to required level. |
