Understanding Field Performance of Hydraulically Fractured Wells:Comparison of Pressure Front versus Tracer Front Propagation Using the Fast Marching Method(FMM)and Complex Analysis Method(CAM)

摘要

This study compares the convective time-of-flight(calculated using the Complex Analysis Method,CAM)and the diffusive time-of-flight(calculated using the Fast Marching Method,FMM)in unconventional reservoir models.The convective time-of-flight determines the drained rock volume(DRV),which refers to the volume of reservoir rock actually drained due to production.The diffusive time-of-flight determines the propagation of the pressure front,which corresponds to the extent of the drainage volume and leads to various definitions such as the depth of investigation,the limit of detectability and the stabilized zone in the reservoir.The disparity(or lag zone)between the DRV and the drainage volume is quantified for a declining production rate in a modeled shale reservoir.The combined strengths of FMM and CAM are applied to calculate the dynamic growth of the pressure and convective tracer fronts during transient flow around the hydraulic fractures of a multi-stage fractured horizontal well,using data generated from a numerical simulator.The synthetic model uses reservoir and completion parameters typical for wells in unconventional shale reservoirs.Comparison of the DRV from CAM and the drainage volume from FMM shows the extent of the lag zone between the propagating pressure front and the tracer front to be of a large magnitude.A crucial insight is that reservoir areas that are under-going pressure depletion(as shown by the diffusive time-of-flight)will still have significant hydrocarbon volumes present in the reservoir space outside of the calculated DRV.Beyond instantaneous production based diagnostic plots of DRV and drainage volumes,FMM and CAM are used to create flow visualizations to provide a spatial description of these propagating fronts in the reservoir.Novel use of FMM and CAM also allows for insight in recovery factors and instantaneous recovery ratios in unconventional reservoirs.