Transient Transport and Flowback Behavior of Partitioning Tracers in Low-Permeability Reservoirs with a Hydraulically Fractured Vertical Well.

Complex fracture networks pose significant challenges for reservoir characterization and performance prediction in fractured reservoirs. Partitioning tracer tests could provide an efficient method for determining residual oil and evaluating well connectivity; however, the transport mechanism of partitioning tracers in fractured reservoirs remains poorly understood, and the tracer flowback response toward the fractured well still receives insufficient attention. In this work, a comprehensive numerical model that accounts for complex fluid properties and fracture dynamics was established to simulate the transient transport and flowback behavior of such partitioning tracers. More specifically, two types of partitioning tracers were injected sequentially together with the pad fluid and proppant-laden fluid, respectively. Meanwhile, the proposed numerical model takes tracer advection, dispersion, and adsorption into consideration. Then, the sensitivity analyses were conducted to investigate the effect of different factors, including formation permeability, fracture length, fracture conductivity, fracture vertical penetration ratio, and tracer dispersion, on the flowback responses of the two partitioning tracers. The results indicate that, in both the water and oil phases, the tracer injected with the proppant-laden fluid exhibits a higher peak concentration, a shorter time to reach the peak, and a higher cumulative tracer recovery (CTR) compared to that injected with the pad fluid.