Mathematical modeling of formation damage effect during underbalanced drilling operations

Formation damage during underbalanced drilling is created due to the spontaneous counter-current imbibition when drilling mud is in contact with saturated formations. Therefore, it should be appropriately recognized and investigated. The objective of this study is to develop a numerical model to simulate the penetration rate of drilling mud in the formation during underbalanced drilling. Modeling of this phenomenon is done by implementing its formulation through implicit pressure-explicit saturation (henceforth, IMPES) method. To validate the results of the developed model with a pilot study in this field, it is demonstrated that the model performs effectively in determining the penetration range of muds and finding the distribution of drilling mud saturation across the core. Consequently, the degree of damage to the formation through laboratory studies is usually time-consuming and therefore, the developed model can be employed for initial studies. Increasing the unbalanced pressure difference, oil viscosity and porosity will reduce the amount of drilling mud penetration in the formation during underbalanced drilling operations.