An analytical model for inter-well tracer tests in lenticular oil reservoirs

Lenticular reservoirs commonly exhibit severe exploitation problems since they are formed by many small independent hydrocarbon compartments. Tracer tests are in general a decisive tool to determine flow communication characteristics in underground formations. In lenticular reservoirs these tests could be used to determine if production wells are located inside the same lens, where the injector itself is located, or if they are producing from a different lens. This information is fundamental in the design of secondary and improved oil recovery techniques. In this work we present a basic analytical advection–dispersion model to analyze this situation. The system consists in three coupled one-dimensional homogeneous regions representing two independent lenses separated by a very low permeability zone. A tracer pulse is introduced in the first lens and moves toward the second lens crossing the inter-lens zone. The tracer breakthrough curve captures some properties of the system, and particularly from the inter-lens zone such as its length. In this work the sensitivity of the model to the characteristics of this zone, i.e. size, fluid velocity and dispersivity, is examined, and the resulting breakthrough curves are compared against the case when this zone is not present. We found that the breakthrough curve displays differences that in general make it possible to confirm when a production well is located outside the injection lens.

Research Highlights
► A mathematical model for tracer tests in lenticular is developed.
► The model is a tool to determine flow connectivity between the lens where fluid is injected and the lens where the fluid is produced.
► By fitting this analytical model to field tracer breakthrough data, information from the lenses and inter-lens region can be gained.
► By employing this model secondary and improved oil recovering processes in lenticular reservoirs can be improved.