In this paper, we illustrate an approach to underbalanced drilling (UBD) candidate selection based on damage assessment and characterization using dynamic reservoir simulations. A 2-phase, 2-dimensional transient reservoir simulator (eRes UBD) using a control volume finite element approach is used to reflect the reservoir conditions. Because of its unstructured grid formulation, the simulator is ideally suited for investigating near-wellbore phenomena, such as drilling-induced invasive damage. In addition, the simulator is augmented to capture dynamic formation exposure, thus enabling drill-ahead capability. Overbalanced drilling conditions are mimicked using the drill-ahead capability of the simulator by specifying an arbitrary depth-vs-time profile, and the resulting formation fluid distribution is investigated, with specific attention to near-wellbore saturation. The impact of invasive damage on productivity is then examined by putting the well into production. Additionally, the extent of damage, flowback period and return permeability are characterized through perturbing critical reservoir and fluid variables. Representative sector simulation runs exhibit the longer term benefits of UBD as compared to conventional counterparts. The methodology described in the paper can ultimately guide the screening and selection of UBD candidates, and is an important part of value-based selection of UBD candidates.

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