c) We=?
G( Bg − BGi) = GpBg − We We = GpBg − G( Bg − Bgi) We = 75(5.5 × 10 −3 ) − 200(5.5 × 10 −3 ) − (4.1 × 10 −3 ) = 0.126 × 10 9 ft 3 ÷ 5.615 We = 22.8MMbbl
PROBLEM 3.10 Explain why initial calculations of gas in place are likely to be in greater error during the early life of depletion reservoirs. Will these factors make the predictions high or low? Explain.
ANSWER: Reservoir pressure drops during production from the reservoir and this phenomenon increases the Bg and consequently the calculated gas in place has some error from the its real value. Water influx into the reservoir maintains the reservoir pressure and this pressure stabilization will not allow Bg to be increased.
PROBLEM 3.11 A gas reservoir under partial water drive produced 12.0 MMM SCF when the average reservoir pressure had dropped from 3000 psia to 2200 psia. During the same interval, an estimated 5.20 MM bbl of water entered the reservoir based on the volume of the invaded area. If the gas deviation factor at 3000 psia and bottom-hole temperature of 170ºF is 0.88 and at 2200 psia is 0.78, what is the initial volume of gas in place measured at 14.7 psia and 60ºF?
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