and Gas Traps
In a typical
trap, gas accumulates on top of the reservoir as a gas cap over the
oil leg which in turn overlies the water-saturated zone in the
reservoir. This occurs because natural gas is lighter than oil which is lighter
than water. However, all three fluids are often intermingled in parts of the
reservoir. Porosity is the ability of a rock to hold oil and gas like water in a
sponge. Permeability indicates how easily fluids can flow through the rock.
A trap requires
reservoir rock to accumulate the oil and gastypically sandstones, limestones and dolomites
impermeable rock to prevent the oil and gas from escaping
a source for
the oil and gas, typically black waxy shales.
Petroleum Communication Foundation. Our Petroleum Challenge: Exploring Canada's Oil and Gas Industry, Sixth Edition. Calgary: Petroleum Communication Foundation, 1999. With permission from the Centre for Energy.