Remobilization of Natural Gas Trapped by Encroaching Water

Abstract

Abstract Water drive gas reservoirs are frequently abandoned at high pressures which results in low recovery of the initial gas in place. The gas remaining in these reservoirs is trapped as residual gas saturation. The techniques to remobilize a portion of this gas that has been trapped by encroaching water are presented along with a method to evaluate the incremental reserve potential of such reservoirs. The remobilization of the trapped gas requires the production of large volumes of water to lower the reservoir pressure which in turn allows the gas pressure which in turn allows the gas to expand and flow. A new use of the p/z vs cumulative production chart is presented which gives the engineer a quick method to evaluate the feasibility of recovering a portion of the gas that has been trapped by water influx. A field example is presented which illustrates the concepts and techniques. Presented is field data that demonstrates the remobilization of gas that had been trapped by encroaching water. Significant increases in recovery have been experienced at the demonstration field, and ultimate recovery is estimated to be about 8% of initial gas in place greater than was recovered using conventional practices. Also given are actual operating costs and revenue calculations that show the process to be economic at 1990 market process to be economic at 1990 market prices. prices Introduction It has long been recognized that water drive gas reservoirs which are abandoned at high pressures have low recovery efficiencies. This gas that remains in water drive gas reservoirs after the water has displaced the produced gas is an important resource produced gas is an important resource that should be addressed. This resource has all the infrastructure for commercial production. These reservoirs have wells drilled, they have gas pipelines already in place, and the resource is known to exist with no exploration effort necessary. P. 375