Nitrogen Injection Into Water-Driven Gas or Condensate Reservoirs Increases Recovery

Many natural gas and condensate reservoirs are subject to secondary recovery by either water injection or a natural water drive. If the hydrocarbon is the non-wetting fluid, and water the wetting fluid, the hydrocarbon will be trapped by the water. The volume of trapped hydrocarbons at abandonment may be of the order of 20 to 45 percent depending upon the particular reservoir. It was believed that a tertiary recovery process could be applied which would increase the hydrocarbon recovery. Low cost nitrogen might be injected at the water-hydrocarbon contact. The nitrogen would result in miscible displacement with the hydrocarbon. Water would drive and trap the nitrogen, and such could result in an increase in ultimate hydrocarbon recovery. The cost of nitrogen from an air separation plant can be quite low, and the process might be applicable to both onshore and offshore reservoirs. Computer simulation studies have been made to estimate the increase in hydrocarbon recovery which might result from injection of nitrogen into natural gas or condensate reservoirs subject to secondary recovery by either a natural water drive or water injection. The effect of dip-angle, porosity, slug size, permeability, gas-water contact and other variables were studied. It would appear thatmore » the injection of nitrogen may result in an increase in hydrocarbon recovery by 30 to 50 percent. The projected economics of the process appear to be favorable.« less