In this paper, we illustrate an approach to underbalanceddrilling (UBD) candidate selection based on damageassessment and characterization using dynamic reservoirsimulations. A 2-phase, 2-dimensional transient reservoirsimulator (eRes UBD) using a control volume finite elementapproach is used to reflect the reservoir conditions. Because ofits unstructured grid formulation, the simulator is ideallysuited for investigating near-wellbore phenomena, such asdrilling-induced invasive damage. In addition, the simulator isaugmented to capture dynamic formation exposure, thusenabling drill-ahead capability. Overbalanced drillingconditions are mimicked using the drill-ahead capability of thesimulator by specifying an arbitrary depth-vs-time profile, andthe resulting formation fluid distribution is investigated, withspecific attention to near-wellbore saturation. The impact ofinvasive damage on productivity is then examined by puttingthe well into production. Additionally, the extent of damage,flowback period and return permeability are characterizedthrough perturbing critical reservoir and fluid variables.Representative sector simulation runs exhibit the longer termbenefits of UBD as compared to conventional counterparts.The methodology described in the paper can ultimately guidethe screening and selection of UBD candidates, and is animportant part of value-based selection of UBD candidates.
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