11.3.1. Introduction

Interwell passive tracer testing is a powerful tool for the evaluation of secondary recovery projects in oilfield reservoirs. In these projects, water injected into injector wells push the oil to the producer wells from which it is extracted. The water injected patterns are usually very complicated because of the natural heterogeneity of the reservoirs and the mobility differences between water and oil. Channelling of water between injector and producer wells is a very common problem that conspires against achieving acceptable sweep efficiencies. The interwell tracer tests permit this problem to be detected and also to allow some reservoir parameters to be determined.

Owing to the elevated uncertainty associated with the reservoir knowledge, especially later to the waterflooding, there is no need, in an initial phase of interpretation, to assume a very detailed model. Therefore, a simple moment analysis or an analytical solution from a one dimensional model can provide acceptable results about the average residence times and water volumes in many cases.

11.3.2. Objectives

In consequence, employment of the Anduril 2.3 simulator was proposed for estimating the principal parameters from data recorded from an interwell tracer test performed in an oilfield in Argentina. The Anduril 2.3 program has capabilities for both temporal and volumetric analyses. In this instance, it was used to determine the following parameters between different pairs of wells:

• Breakthrough time;

• Mean residence time;

• Peak maximum time;

• Final time;

• Tracer recovery.

From the above mentioned parameters, the following volumetric parameters can be obtained:

• Breakthrough volume;

• Mean swept volume;

• Injected volume at peak;

• Maximum injected volume;

• Pore volume swept between wells.

These parameters are proportional to the ones in the first list (water flow rate is the proportionality factor).