MODELING OF ENRICHMENT OF NATURAL-GAS WELLS BY MEMBRANES

Models are developed to simulate on-site membrane enrichment of natura l gas wells. The models consider transient behaviour of the enrichment process, the effects of permeability functions, flow patterns and sep aration of multicomponent systems. The gas mixture considered in the a nalysis includes CH4, CO2, N2 and H2S. Comparison of models shows that for either flow pattern, the presence of low permeating specie reduce s the final CH4 mole fraction in the enriched mixture. In addition, hi gher CH4 recoveries are predicted by the four-component model than by the binary model. This is a result of the lower driving force for perm eation in the four-component model, caused by lower mole fractions. Si milar behaviour is also predicted for the removal of CO2 and its final mole fraction in the gas mixture. The presence of other fast permeati ng species (H2S) resulted in lower permeation rates of CO2. As a resul t, higher CO2 mole fractions in the gas mixture and lower CO2 removal are predicted by the four-component model. The use of variable permeab ilities versus constant permeability ratio showed similar predictions for some of the system variables with partial matching between model p redictions at either low or high pressure.