Recent advances in tracer technology deliver accurate data in a cost-efficient manner. Tracer applications typically aim to improve reservoir description by solving connectivity questions, to evaluate and derisk the potential for secondary and tertiary recovery processes, along with inflow profiling and allocation of injected water or gas.A previous paper (SPE-164930) presented the strategy and planning of a chemical EOR (CEOR) process for sandstone reservoirs of the Caracara Sur Field, Colombia. The project is moving forward and laboratory studies have been successfully completed to define an optimum alkaline surfactant polymer (ASP) formulation. Along with simulation studies, comprehensive inter-well (IWTT) and single well tracer tests (SWTT) have been carried out to provide valuable input to understand aquifer drift, the reservoir flooding process and to analyse residual oil saturations to waterflood (S orw ). This paper presents these two tracer applications:• IWTTs were performed in Caracara Sur sandstone reservoir zones to characterize aquifer drift.Tracer response was used as input for analysing the implications of chemical dilution by the aquifer and also as an input for history matching, resulting in a more reliable reservoir model. • The results of the first SWTT in Caracara Sur Field (and -to our knowledge -in Colombia), are presented. By measuring S orw , the potential for CEOR application has been confirmed.An ASP one-spot test has subsequently been completed and followed-up by a second SWTT to evaluate the efficiency of the chemical formulation. Results are currently under evaluation but appear favourable. Planning for expanded use of CEOR in Caracara Sur continues. Lessons learnt and best practices for implementing tracer technology in similar fields include:• Use of tracer backflow tests (TBFT) to derisk SWTTs; also the use of FBA passive tracers. • Planning, operating and analysing the results of tracer-tests in-house rather than sub-contracting to third parties increases flexibility, increases internal knowledge and is cost-effective.

Chemical Enhanced Oil Recovery (CEOR) in a multi-layered reservoir environment with moderate to strong natural water-drive is a complex process with associated risks and uncertainties. Reservoir simulation is one of the most important tools available to predict behavior under chemical flooding conditions and to study sensitivities aimed to a cost-effective CEOR process implementation. Key to the success of a reliable reservoir simulation is the application of a de-risking process and the acquisition of important calibration data, such as laboratory core-flood data and field-scale pilot experiments.A CEOR pilot is currently undertaken in the Caracara Sur (CCS) field (Llanos Basin, Colombia) which has an unfavorable mobility ratio and very low water salinity. However challenges exist, such as strong water drive (no water injection experience), high temperature and a complex geological nature (up to 15 reservoir layers that made up of multiple isolated distributary channels). A detailed reservoir simulation model was built to study full field implementation of CEOR in Caracara Sur. The model was calibrated with laboratory tests data, residual oil saturations from Single Well CEOR ASP Well Tracer Test Pilots, injectivity tests and breakthrough times from inter-well tracer tests.The paper discusses the approaches taken for full field modeling of Caracara Sur using commercial software and describes how the data collected from alkaline/surfactant/polymer (ASP) core flooding were up scaled and used in pilot sector modeling and for designing tracer back flow tests (TBFT) and single well tracer tests (SWTT) before and after ASP flooding. The TBFT and SWTT results in a pilot injection well, in the middle of three producers, confirmed the absence of aquifer drift, which was also predicted by pilot sector modeling. The paper explains how the obtained results from the tracer tests (residual oil saturations, breakthrough times) and well injectivity were used to calibrate the full field numerical model for reliable prediction of the effectiveness of the ASP flooding.