Prediction Of Tracer Behavior In Five-Spot Flow

Abstract

Abstract Equations are developed to predict the time of tracer breakthrough, the peak concentration of the tracer, and the general form of the breakthrough curve in a 5-spot flood. It is shown that these results depend on the amount of stratification of the reservoir, the volumes injected and produced, the natural dispersion coefficient of the tracer in the reservoir, the amount of tracer injected, plus all the reservoir volume parameters (i.e. well spacing, porosity, thickness). Many laboratory data are available on the breakthrough characteristics of a 5-spot flood, also much data is available on the natural linear dispersion coefficients of reservoir rock. To derive the equations, these data were combined and several assumptions were made. It was also necessary to graphically differentiate the breakthrough data. Thus it should be recognized that the final equations likely have some error. However, this should not invalidate their use, for the method and logic behind the derivation are sound, and thus the form of the final equations should be close to correct. In this paper, the prediction equations are used in a reverse sense. That is, the detailed tracer production history from a field test is used to estimate permeability variation in a 5-spot. Introduction Tracers have been used for many years in reservoir floods to help the operating engineer understand the flow characteristics. Generally this use has been entirely qualitative. The results of time-of-flight, peak concentrations at the producing wells, concentration history, and directional flow have been used only to substantiate that channelling does nor does not exist. No attempts have been made to predict quantitatively the tracer breakthrough behavior that might be expected from different reservoir characteristics. In the past couple of years it has become apparent that some prediction technique could be well used to supplement the other tools available to the reservoir engineer. It is becoming increasingly important that maximum recovery be obtained from a flood, and any quantitative information about the reservoir can be of help in achieving this maximum. The work reported here is a step in this direction — an attempt to quantify the tracer behavior. Equations are developed to predict the time of tracer breakthrough, the peak concentration of the tracer, and the general form of the breakthrough curve in a 5-spot flood. Tracer production history from a field test are compared to the behavior as predicted by the equations.