# HW3_Key - HW3 Key Problem 1 The main difficulty with this...

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HW3 Key Problem 1: The main difficulty with this problem is that below the bubble point, there is gas dissolved in the oil and oil dissolved in the gas. There are two ways to solve this problem; assuming a black oil (thus no oil is dissolved in the gas) or using a system of 4 equations with 4 unknowns. Black oil solution: The first thing to do with the data (once you assume a black oil) is to calculate the oil FVF. ( ) ( ) / ( ) o o o V p B p RB STB V sc = (no unit conversion necessary since ft 3 /scf = RB/STB) And the 2-phase FVF (Bto and Btg): ( ) ( ) / ( ) t to o V p B p RB STB V sc = 3 ( ) 1 1000 ( ) / ( ) 5.615 1 t tg g V p RB scf B p RB Mscf V sc ft Mscf = Now, to calculate the gas FVF you can use ideal gas law in order to calculate the ratio of the gas volume vs it’s volume at std conditions (this is only true because we’ve assumed a black oil and thus there is no condensation of the gas). Thus, 3 ( ) 1 1000 ( ) / ( ) 5.615 1 g sc g g sc V p TP RB scf B p RB Mscf V sc PT ft Mscf = = (remember the temperatures are pressures must be in absolute units) This gas FVF can be used to convert the amount of free gas at the various pressures into gas at SC. Then, the difference between the free gas at any T and P and the final free gas at SC will be the amount of gas dissolved in the oil (if it hasn’t come out of solution yet, then it must be dissolved in the oil). Thus, the dissolved gas (#5 in Fig 4-10) is given by _ _ _ ( ) ( ) ( ) g dissolved g free g free V p V sc V p = - _ 3 ( ) 1 1000 ( ) ( ) ( ) 5.615 1 g g dissolved g g V p RB scf V p V sc scf B p ft Mscf = -

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(For pressures above the bubble point, B g is not defined; however, V g (p) will be zero and thus all the gas will be dissolved gas (which makes sense since the pressure is above the bubble point. Also, make sure you understand why this comes out to be in scf units) Once we have the amount of gas dissolved in the oleic phase, the solution gas-oil ratio is easily computed by _ ( ) 5.615 ( ) ( ) 1 g dissolved s o V p scf R p V sc STB =
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HW3_Key - HW3 Key Problem 1 The main difficulty with this...

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