EXERCISE 1 (a) Calculate the volume of water an aquifer of 35,000 ft. radius can deliver to a reservoir of 3,200 ft. radius rock and water compressibility under a 1,100 psi pressure drop throughout the aquifer. assume porosity = 0.22. (b) Compare the available influx with the initial hydrocarbon volume of the reservoir. Data: Aquifer radius r 35,000 ft. Reservoir radius r 3,200 ft. Water compressibility c 3.0E-06 psi-1 Rock compressibility c 5.0E - 06 Reservoir thickness h 45ft. Pressure drop AP 1,100 psi Porosity 0.22 Water saturation s 0.25 2. MODELS FOR WATER ENCROACHMENT As we have indicated water influx arises as a result of pressure changes decompressing the aquifer. If the pressure in an aquifer can be calculated then the resulting volumetric changes can be determined from the pressure / volume compressibility relationship The figure 2 below illustrates the pressure profiles in a reservoir aquifer system. It is important to appreciate that these profiles are generated as a result of decompression of the oil and aquifer as a result of well bore production. Aquilter boundary not affected by decreasing pressure ify Aquifer boundary Influenced by pressure decline. Pressure Oil Figure 2. Pressure RESERVOIR AQUIFER distribution in an oil reservoir aquifer system. Wellbore Reservoir outer boundary Aquiter Outer Boundary Before examining the different models we will review the development of equations which enable the pressure, time and distance solution to be obtained 6