A study of the A/M2 limestone formation in the Putumayo and Oriente basins had as its objective estimating the oil production potential of the unconventional reservoir and the estimated resources from an exploration, appraisal, and pilot project. This approach is a paradigm shift for a conventional basin in which there is limited experience in tight or unconventional reservoir development. Despite being a calcareous shale, the A/M2 reservoir shows oil saturation and oil-prone characteristics, with most permeability values below 1 md, indicating the need for an unconventional approach. Vertical fractured wells showed production rates ranging from 50 to 150 B/D of 31°API oil. However, economic production presents technical, operational, and logistical challenges.
This reservoir has been previously studied, evaluated, and developed in the Putumayo Basin near the Ecuadorian border with mixed results. Reserve reports and resource estimations from operators and government agencies and core data were reviewed to determine whether the reservoir should be classified as tight or unconventional based on the permeability to support the A/M2 reservoir potential in Ecuador.
The study involved a comprehensive workflow for designing an unconventional pilot project, leveraging existing data and employing current practices from an Argentinean operator working in the Vaca Muerta formation as reference. This study serves as an initial step to evaluate the potential reserves in the A/M2 limestone reservoir.
Using an unconventional hydraulic fracturing simulator, the fracture geometry for each phase was estimated and equipment, proppant mass, and fluids necessary for implementation were dimensioned. The simulation model used well logs, geomechanics data, and the results of minifrac and diagnostic fracture injection tests and fracturing results from two vertical offset wells, located in the already developed areas of the Oriente Basin.
Finally, the production forecast and the expected recovery are estimated using simulation results obtained from an analytical reservoir model.
