Interpretation of interwell chemical tracer tests in layered reservoirs with limited crossflow

This paper presents a systematic approach to evaluate limited crossflow between layers of a stratified reservoir using interwell chemical tracer test. Previous analytic studies either entail no cross-flow between layers or assumes an established vertical equilibrium across transverse direction (owing to viscous/capillary/gravity driving mechanisms); however, they fail to detect the presence of limited crossflow between layers through a “bridge”; 'bridge' in this study is defined as a pathway through which crossflow takes place with an adjacent layer. Obviously, crossflow may take place through several bridges along a layer. A new formulation is developed to study and detect the limited crossflow. The presence of crossflow is confirmed by a zero-sum change of fraction of total fluid flowing through system layers. We employed both numerical simulation and field examples to verify the proposed method. A transition period is identified during which the fraction of fluid flowing through each layer significantly changes because of crossflow. Our results indicate that tracer test data can be used to evaluate number of bridges and possibly their location(s) along the layer. Identification of crossflow between layers and evaluation of transition zone significantly improves the current efforts to understand reservoir heterogeneity and sweep efficiency. It is expected that the outcome of this research can help design much successful EOR processes.