Petroleum System from Source to Trap
1. PETROLEUM TRAPS http://www.usoilandgas.net/findingoil.htm Hydrocarbons - crude oil and natural gas - are found in certain layers of rock that are usually buried deep beneath the surface of the earth. In order for a rock layer to qualify as a good source of hydrocarbons, it must meet several criteria. Characteristics of Reservoir Rock For one thing, good reservoir rocks (a reservoir is a formation that contains hydrocarbons) have porosity. Porosity is a measure of the openings in a rock, openings in which petroleum can exist. Even though a reservoir rock looks solid to the naked eye, a microscopic examination reveals the existence of tiny openings in the rock. These openings are called pores. Thus a rock with pores is said to be porous and is said to have porosity. Another characteristic of reservoir rock is that it must be permeable. That is, the pores of the rock must be connected together so that hydrocarbons can move from one pore to another. Unless hydrocarbons can move and flow from pore to pore, the hydrocarbons remain locked in place and cannot flow into a well. In addition to porosity and permeability reservoir rocks must also exist in a very special way. To understand how, it is necessary to cross the time barrier and take an imaginary trip back into the very ancient past. Imagine standing on the shore of an ancient sea, millions of years ago. A small distance from the shore, perhaps a dinosaur crashes through a jungle of leafy tree ferns, while in the air, flying reptiles dive and soar after giant dragonflies. In contrast to the hustle and bustle on land and in the air, the surface of the sea appears very quiet. Yet, the quiet surface condition is deceptive. A look below the surface reveals that life and death occur constantly in the blue depths of the sea. Countless millions of tiny microscopic organisms eat, are eaten and die. As they die, their small remains fall as a constant rain of organic matter that accumulates in enormous quantities on the