Performance evaluation of CO2 Huff-n-Puff and continuous CO2 injection in tight oil reservoirs

The CO2-enhanced oil recovery (EOR) effectiveness was simulated and analyzed by comparing Huff-n-Puff and continuous injection scenarios. A field-scale numerical compositional reservoir model was built based on typical fluid, reservoir, and fracture properties from the Middle Bakken Formation. The effect of matrix permeability ranging from 0.001 mD to 0.1 mD on the comparison of well performance of these two scenarios was investigated. A critical value of permeability was identified. When the permeability is lower than 0.03 mD, the CO2 Huff-n-Puff performs better than the continuous CO2 injection. Subsequently, experiment design and response surface methodology was used to perform sensitivity studies with four uncertain parameters including matrix permeability, number of wells, well pattern, and fracture half-length. The results show that the matrix permeability is the most significant parameter, followed by well pattern and the interaction between fracture half-length and number of wells. Furthermore, three diagnostic contour plots corresponding to 4, 6, and 8 horizontal wells per square mile were generated. Based on these plots, it is convenient to identify the best zone with better CO2-EOR effectiveness for different CO2 injection scenarios. This study can provide a very useful tool for a better understanding of CO2-EOR strategy determination in tight oil reservoirs.