Prediction of formation damage that occurs while drillinghorizontal wells is a critical point for optimising an oil fielddevelopment. The economic impact of near wellbore drillinginduceddamage and clean up efficiency has led to makesignificant progress in both experimental and numericalstudies in order to assess wellbore flow properties during oilproduction. As a result, a numerical model has been developedto study the impact of various parameters related to theproperties of drilling fluids on the well inflow performance.This paper describes a numerical approach developed inthis model to simulate near wellbore formation damage due tounderbalanced (UBD). It is generally expected that UBD willbe of benefit from preventing formation damage. However,this benefit can be lost for various reasons. For instance, anoverbalanced pressure can be applied on the formation duringshort periods of time for various operational reasons and it cancause a severe formation damage due to the absence ofexternal cake protection and huge filtrate invasion. Anotherpossible cause of formation damage in UBD is related tospontaneous imbibition which induces water blocking,experienced while drilling tight gas reservoirs.A methodology for the modelling of possible formationdamage during UBD is presented. Cross flow phenomena dueto spontaneous imbibition is taken into account to model thefiltrate invasion from the well to the porous media as the wellis producing.
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