Question:medium

A gas reservoir has a bulk volume of 10000 ft\(^3\), a connate water saturation of 0.2, and a porosity of 0.2. No oil is present in the reservoir. The gas formation volume factor Bg is 0.005 RCF/SCF. The volume of gas in place (in SCF) is ________ x 10\(^4\). [RCF: Reservoir Cubic Feet; SCF: Standard Cubic Feet]

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Gas in place equals pore volume times (1 minus connate water saturation), divided by the gas formation volume factor Bg.
Updated On: Jul 28, 2026
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Correct Answer: 32

Solution and Explanation

Step 1: Find the pore volume and the gas filled portion of it:
Pore volume is bulk volume times porosity: $PV = 10000 \times 0.2 = 2000$ ft$^3$. Of this pore space, a fraction 0.2 is occupied by connate water and cannot hold gas, so the gas occupies the remaining fraction: $HCPV = 2000 \times (1 - 0.2) = 1600$ ft$^3$ of reservoir gas volume.
Step 2: Define the gas expansion factor as the reciprocal of Bg:
Instead of dividing by Bg directly, define the gas expansion factor $E = 1/B_g$, which tells you how many standard cubic feet one reservoir cubic foot of gas expands into when brought to surface conditions. Here $E = 1 / 0.005 = 200$ SCF per RCF.
Step 3: Multiply the reservoir gas volume by the expansion factor:
The gas in place at standard conditions is the reservoir gas volume multiplied by how much each reservoir cubic foot expands to at the surface: $G = HCPV \times E = 1600 \times 200 = 320000$ SCF. This is the same result as dividing by Bg directly, since multiplying by $1/B_g$ is identical to dividing by $B_g$, and it confirms the earlier calculation.
Step 4: Express the result in the requested units of 10\(^4\) SCF:
$320000$ SCF divided by $10000$ gives $320000 / 10000 = 32$.
Final Answer:
\[ \boxed{32 \times 10^4 \text{ SCF}} \]
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