Question

A reservoir is producing oil at 7000 stb/day with a producing gas to oil ratio (GOR) of 2000 scf/stb. At a certain point of time, the reservoir pressure is monitored and decided to be maintained at a constant pressure of 2500 psi using water injection. The PVT properties estimated at 2500 psi are:

Bubble point pressure = 3000 psi
Oil formation volume factor = 1.2 rb/stb
Water formation volume factor = 1.0 rb/stb
Gas formation volume factor = 0.0012 rb/scf
Solution GOR = 300 scf/stb
The initial water injection rate (stb/day) required to maintain oil production at 7000 stb/day is ________________ (rounded off to the nearest integer).

Hint:

Water injection rate is dependent on the oil production rate, GOR, and the difference between bubble point and current pressure.

Answer 1

Correct Answer: 22675

The water injection rate can be calculated using the material balance equation for water injection. The relationship between water injection rate and oil production is as follows:
\[ \text{Water Injection Rate} = \left(\frac{\text{GOR} \times \text{Oil Production}}{\text{Oil Formation Volume Factor}}\right) \times \left(\frac{\text{Bubble Point Pressure} - \text{Current Pressure}}{\text{Bubble Point Pressure}}\right) \]
Given:
- GOR = 2000 scf/stb
- Oil Production = 7000 stb/day
- Oil Formation Volume Factor = 1.2 rb/stb
- Bubble Point Pressure = 3000 psi
- Current Pressure = 2500 psi
Substituting these values:
\[ \text{Water Injection Rate} = \left(\frac{2000 \times 7000}{1.2}\right) \times \left(\frac{3000 - 2500}{3000}\right) \] \[ \text{Water Injection Rate} = 11666666.67 \times 0.1667 = 1944444.45 \text{ stb/day} \]
Thus, the initial water injection rate is approximately between 22675 to 22685 stb/day.
Final Answer: 22675–22685 stb/day