Guidelines for developing gas fields associated with edge-water drive

The objective of this work is to investigate the effects of key reservoir and aquifer parameters on gas recovery factor for finite and infinite aquifers. The first part deals with performance calculations of cumulative water influx and cumulative gas production at successive time steps. The effects of aquifer size to reservoir size ratio, rate of pressure depletion at the gas/water contact, initial pressure at the gas/water contact, initial gas in place, angle of water encroachment, and volumetric sweep efficiency on the cumulative water influx and cumulative gas production are investigated. In the second part, a new analytical approach is proposed to determine abandonment pressure and gas recovery factor for the case of infinite aquifers. The third part caters for performance calculations of gas recovery in the case of finite aquifers. For this purpose, another new analytical approach is suggested for estimating the rate of pressure depletion at the gas/water contact. It is concluded that the reservoir and aquifer parameters considered in this study can significantly affect, to a varying degree, the amounts of water influx and gas production. For infinite aquifers, higher rates of pressure depletion at the gas/water contact are found to yield higher gas recovery factors, less number of lbm-moles of remaining gas in the reservoir, and lower abandonment pressures. For finite aquifers, higher ratios of aquifer size to reservoir size are shown to yield higher abandonment pressures and larger number of lbm-moles of remaining gas in the reservoir at abandonment conditions. The gas recovery factor, however, is found insensitive to the ratio of aquifer size to reservoir size. The results of this work can be of great value to reservoir and production engineers dealing with this type of gas reservoirs and should provide them with the necessary guidelines for planning their production strategies.