Designing an Inter-Well Tracer Test in Produced Water Reinjection Fields

Abstract Inter-well tracer test (IWTT) is a method used to track the movement of injection fluid and identify the field connectivity. The mechanism of IWTTs consists of injecting slugs of tracer in the water injector and observing the tracer at the producers from water samples. One of the advantageous of the IWTT is the uniqueness of tracers which indicates to a specific tracer origin. However in fields which apply produced water reinjection, the original location of the tracer might not be determined. This is caused by the reinjection of produced tracer in other injectors. The tracer reinjection could add noises to the tracer data which might lead to misinterpretations. The basic idea to overcome this problem is to minimize the noises so that it cannot be detected. It could be achieved by maintaining the noise level under the detection limit of the analytical tool (gas chromatography/mass spectrometry). The noise created from the tracer reinjection is directly proportional to the amount of tracer being re-injected and the amount of tracer being re-injected is directly proportional to the initial amount of tracer being injected in the first injector. Therefore in order to minimize the noises, the initial tracer amount should also be minimized. However, too little amount of tracer might prevent the tracer from being observed in the target producers. This paper discusses the methodology in optimizing the tracer amount. There are basically 4 criteria that need to be considered in optimizing the tracer amount. First, the tracer amount should be sufficient for the tracer to be detected in the target producers. Second, the tracer amount should be minimal to keep the noises below the detection limit. Third, the tracer amount should also results in minimum delay of tracer reading in the producers. The last criterion is to keep a minimum cost for the IWTT project. This methodology has high potentials to serve as a guideline for reservoir engineers when designing an IWTT in PWRI fields. In conclusion, by having a proper design, the IWTT in PWRI fields can give the same benefits as in the non-PWRI fields.