Enhanced gas recovery from watered-out reservoirs

Major additions to future gas reserves will depend partly on development of resources that are presently unconventional. Recently, coproduction of gas and water has been proposed as a method to increase ultimate gas recovery from reservoirs that have begun to water out or were abandoned because of high water production. The enhanced recovery method involves producing large volumes of water and reducing reservoir pressure to the point where dispersed gas, trapped in the water-invaded zone, is mobilized and flows to the well bore. Integration of geological and engineering studies indicates that the Port Arthur field in Jefferson County, Texas, is a prime area for research to test the coproduction techniques. The reservoirs are relatively narrow and elongate and are oriented nearly perpendicular to the local structure, a simple rollover anticline. The C sandstone was selected for detailed investigation because of high abandonment pressure, excellent reservoir quality, high productivity, and good lateral continuity. Reservoir simulation studies suggest that 5.5 bcf of gas and some condensate could be recovered from the C sandstone under natural flow conditions by producing slightly more than 9 million bbl of water over a 5-year period. Brine disposal would be accomplished by injection into thick Miocene sandstonesmore » that occur at shallow depths. If successful, the recovery efficiency of the C sandstones would be increased from 42% (primary) to 53% of the original gas in place. An economic analysis of the enhanced recovery project indicates a favorable payout under prevailing gas prices.« less