In unconventional reservoirs that rely on hydraulic fractures for production, displacement Enhanced Oil Recovery (EOR) methods are difficult to apply due to the low matrix permeabilities that impede the flow of the injected agents through the formation. This leaves cyclic methods, also known as huff-and-puff as one of the possible alternatives for improving recovery in these types of reservoirs.
Since 2014, a considerable amount of literature and research has been devoted to the feasibility, implementation and optimization of gas Huff-and-Puff in fractured unconventionals. Most of these studies have been devoted to oil reservoirs and few publications have addresses gas condensates.
In this study, we investigate the feasibility of using lean hydrocarbon gas mixtures to increase recovery in a typical gas condensate reservoir in the Montney formation. To perform this study, we used publicly available data to build a representative Montney gas condensate reservoir. A finite-element hydraulic fracture simulator was employed to create a series of hydraulic fracture geometries that were later modeled with a compositional reservoir simulator to forecast primary production and liquid recovery under different Huff-and-Puff scenarios. We conducted sensitivity studies to test the effect of the injected gas composition and soaking time. Additionally, the impact of fracture geometries (complex vs. planar) was also investigated.
We found that soaking time had a measurable effect on liquid recovery as it allows the pressures between the fractures and matrix to equilibrate, thereby affecting the volume of condensate that can revaporize. The choice of solvent has a strong effect on the amount of condensate uplift, with leaner gasses recovering less. Finally, higher incremental liquids production with Huff-and-Puff was strongly correlated with higher pressures since they allowed for more re-vaporization. Fracture geometries were found to have considerable influence on the pressure profiles during the production and injection periods; therefore, the degree of complexity of the fracture played a role in the performance of the EOR process.
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