Interpretation of Interwell Chemical Tracer Tests in Layered Heterogeneous Reservoirs with Crossflow

Abstract

Abstract This paper presents a systematic approach to evaluate limited crossflow between layers of a stratified reservoir using interwell chemical tracer test. Previous studies either entail no crossflow 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 apathwaythrough 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 crossflow is detected through monitoring of the fraction of total injected fluid that arrives at the producer from each layer as a function of time. We employed both numerical simulation and field examples to verify the proposed method. A transition period is identified during which thefraction of injected fluid flowing through each layer significantly changes because of crossflow. Our results indicate that tracer can be used to evaluate number of bridges. The distance between injector and the bridge location can significantly change the interwell tracer results. Identification of crossflow between layers and evaluation of transition zone significantly improves the current efforts to understand reservoir complexity and sweep efficiency. The outcome of this research can help design more successful EOR processes.