Prediction of reservoir performance during water displacement process is a routine procedure for homogeneous reservoirs but complicated in stratified heterogeneous reservoirs. Most analytical methods assume the simplistic no-crossflow condition while models that incorporate crossflow use numerical techniques which are not very amenable to routine calculations. In this study, by using the concept of pseudo-relative permeability, the effects of crossflow and stratification were incorporated into the fractional flow equation for reservoir performance evaluation and tracked using the well-known Welge analysis procedure. Application to field examples confirmed observations of previous researchers that reservoirs with favorable end-point mobility, crossflow between layers can enhance oil recovery (by more than 10%), while unfavorable end-point mobility leads to significant reduction (over 20%) in oil recovery. The study therefore confirmed that the Welge analysis front tracking method has wider scope of application than currently used and can be extended to stratified crossflow reservoirs without loss of accuracy.
Keywords: crossflow, cumulative oil produced, fractional flow, frontal velocity, heterogeneous reservoir, pseudo-relative permeability
