Tracer technology has evolved significantly over the years and is being increasingly used as one of the effective tools in the reservoir monitoring and surveillance toolbox in the oil and gas industry. Tracer surveys, conducted either as inter-well tests or single-well tests, are one of the enabling technologies that can be deployed to investigate reservoir flow performance, reservoir connectivity, residual oil saturation and reservoir properties that control displacement processes, particularly in improved oil recovery (IOR) and enhanced oil recovery (EOR) operations.
As part of the comprehensive monitoring and surveillance program for an IOR injection pilot project in a Jurassic age reservoir, an inter-well chemical test (IWCTT) was designed and implemented to investigate reservoir connectivity between injector and producer well pairs, water breakthrough times (“time of flight”), and possible inter-well fluid saturations. Four unique tracers were injected into four individual injectors, respectively, and their elution were monitored in the four “paired” up-dip producers.
In addition to the reservoir connectivity and breakthrough times between the injector and producer pairs, the results showed different trends for different areas of the reservoir. A detailed analyses of the exit age distribution and residence time distribution (RTD) curves showed two peaks for three of the injector-producer pairs and a single peak for the last pair. These were reflective of some apparent reservoir heterogeneities that were not anticipated at the beginning of the pilot.
This paper reviews the complete design and implementation of the tracer test, field operational issues, analyses, and interpretation of the tracer results. The tracer data has been very useful in understanding well interconnectivity and dynamic fluid flow in this part of the field. This has led to better reservoir description and an improved dynamic simulation model.
The use of tracers to monitor transport processes is a generic and versatile technique with a range of applications. In the subsurface domain, it has been used extensively in ground-water applications, as well as to monitor and optimize hydrocarbon reservoir production. For a general review of tracer applications in oil and gas reservoirs, see Zemel (1994). Interwell tracer applications were reviewed by Dugstad (2007).
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