Pressure Profile Estimation through CFD in UBD Operation Considering with Influx to Wellbore

Nowadays, UnderBalanced Drilling (UBD) technology is widely applicable in the petroleum industry due to its advantages to an overbalanced drilling operation. UBD success depends on maintaining the drilling fluid circulating pressure below the reservoir pore pressure during operations. One of the main prerequisites of a successful UBD operation is the correct estimation of the pressure profile. In this investigation, the pressure profile was obtained with consideration of the influx to the wellbore. A spreadsheet was developed to obtain the pressure profile using an analytical solution for aerated mud in UBD operation. Moreover, a numerical simulation was employed to simulate the three-phase flow in annulus through the UBD operation and the transient Eulerian model flow via the turbulence k-ε model. The effects of solid particle size and rotation of the inner pipe were considered on the pressure drop. It was observed that pressure drop was significantly increased with increasing solid particle size while it remained almost constant with increasing of the inner pipe rotation. The analytical and numerical results were compared with published experimental results and showed a good agreement.