At discovery, what would the pressure be in a black oil reservoir?

At discovery, what would the pressure be in a black oil reservoir?

• A. Below the bubble point pressure
• B. Exactly at atmospheric pressure
• C. Above the bubble point pressure
• D. Above the bubble point pressure or equal to the bubble point pressure

Answer: (D)

The situation hinges on the bubble point concept: in a black oil system, gas is dissolved in the oil as long as the reservoir pressure stays above the bubble point. The bubble point is the pressure at which gas begins to exsolve from the oil and form a separate gas phase. At discovery, the reservoir is typically under high pressure, so the oil remains a single liquid with dissolved gas. That means the pressure is at or above the bubble point. If you drop below the bubble point, gas would start to come out, creating a gas phase, which isn’t the initial condition at discovery. And atmospheric pressure is far from typical reservoir conditions, which are far higher than surface pressure.

The situation hinges on the bubble point concept: in a black oil system, gas is dissolved in the oil as long as the reservoir pressure stays above the bubble point. The bubble point is the pressure at which gas begins to exsolve from the oil and form a separate gas phase. At discovery, the reservoir is typically under high pressure, so the oil remains a single liquid with dissolved gas. That means the pressure is at or above the bubble point. If you drop below the bubble point, gas would start to come out, creating a gas phase, which isn’t the initial condition at discovery. And atmospheric pressure is far from typical reservoir conditions, which are far higher than surface pressure.