Classification and interpretation models of inter-well chemical tracer monitoring for fractured ultra-low permeability oil reservoirs

In fractured ultra-low permeability oil reservoirs, natural fractures are well developed, while artificial fractures make the fracture systems more complicated. As waterflooding is further promoted in development, the fracture systems change dynamically. The current porous tracer interpretation model cannot be used to effectively characterize such water-channeling fracture systems. In this paper, the general characteristics of water-channeling and water-flooded fracture systems were analyzed for the fractured ultra-low permeability oil reservoirs in the Ordos Basin. The water-channeling fracture systems were divided into three types, i.e. artificial fractures communicated, different fractures interacted, and fractures advanced evenly, and then the physical model was devised equivalently for each type of water-channeling fracture system. Based on the basic assumptions for movements of injected water and tracer in fracture strips, three classes of tracer interpretation models were established for water-channeling fracture systems, i.e. Class I (single-peak), Class II (multi-peak) and Class III (wide-platform). In this way, heterogeneity-related problems were treated as relative homogeneity. Field cases proved the rationality and applicability of these models in tracer interpretation for fractured ultra-low permeability oil reservoirs. The tracer classification and interpretation models can provide important evidences for accurately preparing the water-channeling and water-flooding treatment schemes and thoroughly tapping the potential of fractured ultra-low permeability oil reservoirs.