Analysis of an Interwell Tracer Test in a Depleted Heavy-Oil Reservoir

Abstract

Summary This paper presents field data and analyses of an interwell tracer test conducted in the Niitsu oil field, which is a fully depleted heavy-oil reservoir of unconsolidated sand formation. Water containing a chemical tracer was injected at a constant rate into an injector surrounded by three production wells. Effluent analyses showed very early breakthrough of injected water at two of the producing wells. The test results suggest a strong areal heterogeneity of the tested formation. An appropriate analytic model was used to obtain a preliminary interpretation of the results. A modified three-dimensional (3D) black-oil model developed to simulate the polymer flood process was then used for analyzing the data in more detail. The model treats tracer solution as a fourth component and can also account for adsorption of tracer. Simulation efforts were concentrated on matching the breakthrough times and tracer profiles after breakthrough. Through both the analytic and the simulation work, the reservoir is characterized by a highly heterogeneous distribution of horizontal permeability, a thin layer of high permeability, and a natural waterdrive that cause a preferential flow trend in a direction toward one producer. We conclude that the interwell tracer test is an effective tool for evaluating reservoir heterogeneities and a quantitative analysis of test data is done with the polymer option of a black-oil simulator.