Reservoir Simulation of Primary and Enhanced Oil Recovery by Huff and Puff Gas Injection, and CO2 Storage in La Luna Shale of Colombia
Authors: Tellez C. Herrera , Fragoso A. , Aguilera R. 
Published: June 2023

Abstract
La Luna Shale in Colombia has significant oil and gas potential in the Middle Magdalena Valley and Catatumbo Basins that can be developed with the use of hydraulically fractured horizontal wells. This potential, however, has not been fully evaluated. Thus, this paper concentrates on estimating La Luna's primary and enhanced oil recovery, as well as the potential for CO2 storage with the use of reservoir simulation.
Simulation of enhanced oil recovery is conducted in this study using CH4 and CO2 as injected gases during huff and puff (huff ‘n’ puff) operations. Simultaneously, the study simulates the viability of using La Luna Shale as a safe place for storing CO2 with negligible possibilities of unwanted leaks. The selection of La Luna Shale for this purpose stems from the observation of geologic containment in La Luna.
Geologic containment is a concept developed by our research group at the University of Calgary. Our study concludes that geologic containment occurs in La Luna Shale, where natural gas, condensate and oil are upside down or in an inverted position in the structure. The paper demonstrates that if the hydrocarbons remain in the same position where they were generated, then the possibilities that the injected gases will leak beyond the volume that is hydraulically fractured are nil.
Simulation results reveal that primary recovery from La Luna Shale for the investigated areas range between 23 to 25%. These recoveries are much larger than those reported for the Eagle Ford Shale of Texas, which range between 5 and 10%. Higher quality of La Luna shale is associated with these significant recoveries, which are supported by production data from La Luna and Eagle Ford shales. Simulation results show that these recoveries can be improved by huff ‘n’ puff gas CO2 injection.
The simulation further shows that during successive cycles of huff ‘n’ puff with CO2, the volume of CO2 retained in La Luna is progressively larger. Once huff ‘n’ puff reaches its economic limit, CO2 can be injected continuously until reaching a maximum pressure equal to the initial reservoir pressure. CO2 injected is thus stored safely and permanently in La Luna Shale.
The novelty of the paper is demonstrating that geologic containment exists in La Luna Shale in both the Middle Magdalena Valley and Catatumbo basins of Colombia. Under these conditions, and given the quality of La Luna Shale, reservoir simulation shows that La Luna primary oil recoveries can be significant and can be improved by huff ‘n’ puff CO2 injection. Furthermore, the advantage of using CO2 is that it can be stored safely and permanently with negligible possibilities of unwanted leaks. Thus, La Luna shale can contribute with two important segments of CCUS: (1) Utilization of CO2 for Enhanced Oil Recovery (EOR) and (2) Storage of CO2 as shown in this paper. The segment associated with Capture of CO2 can be accomplished from refineries and large industrial complexes. This, however, is beyond the purpose of the present study.