Numerical Simulation of the Storage of Pure CO2 and CO2-H2S Gas Mixtures in DeepSaline Aquifers

摘要

We have studied strategies for maximizing several phenomenabeneficial to large-scale subsurface storage of waste gasessuch as CO2 and H2S. Numerical simulations using acompositional reservoir simulator were carried out for 10,000years to understand the flow and long-term storage potential ofpure CO2 and CO2-H2S mixtures in deep saline aquifers.Hysteresis in the relative permeability curve results insubstantial volumes of gas trapping. Aquifer characteristicssuch as heterogeneity, dip angle and vertical to horizontalpermeability ratio were varied to determine their effect onstorage potential and injectivity of a CO2-H2S gas mixture.The opportunity for escape of the gases from the aquifer canbe minimized by careful design of injection strategies. Onesuch strategy is to use horizontal wells low in the formation sothat all of the injected gases are trapped, dissolved orprecipitated before they reach geological seals and/or faults.This allows significantly larger volumes of waste gases to bestored in a given aquifer. Preferential solubility of the H2S inbrine reduces the distance H2S travels relative to CO2.Simulations with local grid refinement show that fingering dueto buoyancy is mitigated by natural heterogeneity in theaquifer petrophysical properties. Thus the amount of gastrapping observed in coarse-grid simulations is likely to be areasonable estimate of what can be obtained in the field.Three-dimensional simulations of coupled flow and reactivetransport showed that the amount of CO2 sequestered asminerals was small relative to gas trapping and dissolutioninto brine. However, the mineralization further reduces thealready small amount of mobile gas over long periods of time.