When the well reaches a pool, oil usually rises up the well because of its density difference with water beneath it or because of the pressure of expanding gas trapped above it.

Both oil and gas are less dense than water, so they generally tend to rise upward through water-saturated rock and sediment.

The water would exert less pressure on the oil and gas down below, which is why it was important that 【concrete seals】 were in place to avoid any blowout.