Chemical Tracers as a Tool for the Optimum Development of Mature Reservoirs in the Presence of a Strong Active Bottom-water Drive: Villano Field – Ecuador
Authors: Andrade Alejandro , Correa Ramón , Ippoliti Massimo , Chango Mario , Villaseñor Ricardo 
Published: November 2015

The objective of this paper is to describe the application of chemical tracing technology in two different water injection campaigns, 2010 and 2014, as a tool for the future development (e.g., infill wells) and water production optimization of the mature Hollin reservoir in Villano Field, taking into account the presence of a strong, active, bottom-water drive. Both interwell tracer studies were useful in evaluating reservoir heterogeneity, identifying interwell communication between disposal and production wells, reservoir layering, flow barriers, and determining the injected water distribution and swept pore volume. These studies prove that disposal water recirculates and that the previous campaign i.e. tracers from 2010 can remain within a reservoir for as long as 4 years, especially when large volumes are injected.

The methodology employed and the results obtained in both campaigns performed at different times in the Villano Field (i.e., 2010 and 2014), allows the quantification of interwell communication along with the amount of water recirculating in disposal wells. The procedures described will include the project design, tracer injection, sampling schedule, and analysis of the project data. Also, the analysis results obtained include additional samples used to verify that the water was recirculating and that the tracer data was incorporated into the dynamic simulation model. Finally, applying the chemical tracer information from one re-injection well in 2010 that was later converted to a production well in 2014; the chemical tracers were used as a field scale production log to identify the source of produced water for future water shut off intervention.

The 2010 chemical tracer project was initially developed for a pilot Waterflooding with two re-injectors (V-2 and V-5) to evaluate the possibility to have an additional oil recovery in a specific pay zone in to the reservoir. However the data obtained such as swept pore volumes (low values) was an indication of poor sweep efficiency it means that this kind of reservoirs within the aquifer water influx is not the better scenario to swept oil from Re-injectors to producers. At the other hand the project proved and quantified the interwell (disposal/producer) communication between disposal and production wells. The percentage of traced fluid recycled in the disposal wells was around 4% and 33% for the re-injectors., this despite the presence of the strong active bottom-water drive.

The 2010 campaign also identified a strong interwell communication between one disposal and one production well, which was proven with the injection and production data. Based on this information, it was decided to perform a water-shutoff, which successfully results, isolating the connection between the wells.

Normally, chemical tracers are used for Waterflooding projects. In the case of Villano Field, the mentioned pilot project show that is an adverse condition to recover more oil by injecting water. However, the technology was fully applicable in the qualitative and quantitative determination of interwell communication. Based on this data, a better decision could be made to improve water handling in a 100% producer/re-injector scenario.

The 2014 chemical tracer project had as main objective to investigate the possible interwell communication in the southern area of the reservoir, which was considered critical in defining the target locations for future infill drilling wells. Moreover, analysis showed that tracers, from the previous campaign in 2010, were still being found in some production wells.