Question

For a hydrocarbon reservoir, the following parameters are used in the general material balance equation (MBE). 

The total pore volume (in rb) of the reservoir is:

• A. \( G B_{gi} \left( 1 + m \right) \frac{1}{1 - S_{oi}} \)
• B. \( N B_{oi} \left( 1 - m \right) \frac{1}{1 - S_{oi}} \)
• C. \( N B_{oi} \left( 1 + m \right) \frac{1}{1 - S_{wi}} \)
• D. \( G B_{gi} \left( 1 - m \right) \frac{1}{1 - S_{wi}} \)

Hint:

In reservoir engineering, understanding the relationship between oil, gas, and water volumes is key to calculating the total pore volume. Always ensure you use the correct values for the oil formation volume factor and water saturation in your calculations.

Answer 1

The Correct Option is C

In a hydrocarbon reservoir, the total pore volume is a combination of the initial volumes of oil, gas, and water. The formula used in the general material balance equation helps account for the volume occupied by these phases. Specifically, it accounts for the oil volume in place \( N \), the oil formation volume factor \( B_{oi} \), and the water saturation \( S_{wi} \), which describes the amount of water present in the reservoir.
The term \( m \) represents the ratio of the initial gas cap volume to the oil volume, and the total pore volume is influenced by both the oil and gas volumes. This relationship is captured by the formula: \[ {Total Pore Volume} = N B_{oi} \left( 1 + m \right) \frac{1}{1 - S_{wi}} \] This equation takes into account the volume of oil and gas, along with the water saturation, to give an accurate calculation of the total pore volume in the reservoir. It’s critical for understanding how the different phases in the reservoir will affect the total capacity and flow behavior. Thus, the correct answer is option (C), which correctly represents this relationship.