Upscale methodology for gas huff-n-puff process in shale oil reservoirs

Results of recent laboratory experiment studies suggest that huff-n-puff gas injection holds great potential to increase oil recovery from shale oil cores. However, our current knowledge of the field-scale performance of this process is very limited. Reservoir simulation is required to properly upscale this process from laboratory to field conditions in order to predict oil recovery and reduce the risk of failure in field projects. After examining the literature, the purpose of all upscale methods is to generate a single curve which can describe the relationship of oil recovery versus dimensionless time for different scales. For a gas huff-n-puff process applied in a shale oil reservoir, it is also necessary to generate one single type curve to upscale a lab experiment to field-scale production. In this paper a new expression of dimensionless pressure was generated to describe the huff-n-puff efficiency, and a new version of dimensionless time was also derived that includes dimensionless pressure, permeability, porosity, viscosity, and core length. A compositional numerical model with dynamic gridding was built and validated by matching the experimental data, and the model was then used to test the upscale methodology. Several validation tests were conducted for different fluid and rock parameters, well constraints, and operation schedules. To this end, a type curve was developed for different scales which demonstrates that all sizes yield a similar relationship between oil recovery and dimensionless operation time. It proves that the cumulative oil recovery of gas huff-n-puff EOR in shale oil reservoirs can be predicted. In a case of high-permeability, the curve between oil recovery and dimensionless time deviates from the type curve (moves to the right side). This indicates huff and puff times are too long, and the process is inefficient. In this case, the huff and puff times can be reduced so that the curve follows the generated type curve.