Utilization of aquifer storage in flare gas reduction

Flaring associated gas from oil wells has resulted in concerns about CO2 emissions and wasted energy. In this paper, an integrated flare gas reduction system that combines natural gas liquids separation and underground storage of lean gas in aquifers is studied. This flare gas reduction system takes advantage of peak natural gas demand and prices in winter. Therefore, revenues from both lean gas natural gas liquids sales would compensate for the year-long natural gas liquids separation costs. Aquifer permeability and depth are the major factors in determining the storage cost, which should be lower than the marginal revenue derived from the seasonal difference in natural gas prices. The site selection method and governing equations are presented, and a case study applying the proposed system to the Bakken oil field was performed. The results indicated that when aquifer permeability was low (<200 mD), permeability had a larger impact on the storage cost than aquifer depth, and the cost decreased with increasing permeability and depth. When aquifer permeability was relatively high (>200 mD), depth was the dominating factor and the cost increased with depth. Ranges of permeability and depth for which the storage cost is lower than the seasonal price difference of natural gas were determined. The economic estimation approach presented in this paper can be used to select appropriate storage sites and rich gas processing technologies.