La Cira Infantas is the oldest oil field in Colombia with approximately 100 years of production history, located in the Middle Magdalena Valley Basin. The field production comes from the C zone reservoir of Mugrosa Formation where the depositional environment is a fluvial meandering system. The reservoir has a high heterogeneity and it is defined as an interbedding of sandstones, shales and siltstones with an average thickness of 600 ft and a permeability range from 80 mD to 2 Darcy. The field has been under secondary recovery since the 1960's and in 2005 a redevelopment of the water flooding process began. The field has approximately 400 patterns and 1,000 active producer wells, 95% of which are under a water flooding process. Injector wells have a selective string completion, composed of mandrels and packers, independently injecting in different sand units. Currently, there are patterns with low areal efficiency and consequently lower than expected recovery factor. An interwell tracer project was executed in a six pattern pilot sector, composed of 16 distinct mandrels, in order to validate the need of a conformance treatment to improve current conditions and have a better understanding of the reservoir connectivities. In each selected mandrel a unique tracer family was used in order to accurately intepret breakthough results.
The workflow in the project starts by using the results of the tracer test to estimate swept volume and flow geometry in all patterns. The swept zone represents the thief zone in each pattern and provides an insight of how poor the areal efficiency of the pattern is. Flow geometry is represented in an F- Φ curve and the tangent is related to the residence time of an arbitrary flow line, which is used to first recognize the need for a conformance job and then to calculate the fraction of the swept volume needed to treat. The last step of the workflow is to estimate the incremental oil production rates derived from treating the thief zone. Two analytic methods were derived for the incremental oil production rate estimates. The conformance candidates were ranked according to treatment volume vs. incremental oil recovered over a two-year timeframe. Those results are in process of being analyzed.
The results of the inter-well tracer showed that conformance is needed in 6 individual mandrels and there is a strong relationship between the facies architecture and the flow distribution of the injected water. Also, it will improve the definition of the job portfolio for the conformance project which considers 80 candidates and 2.7 MMBO resources.
The application of conformance treatments is a novelty in multilayer mature oil fields under water flooding process in Colombia, and the study of inter well tracers is essential for the success of this IOR technology.