Introduction what is petroleum?

Petroleum is a naturally occurring hydrocarbon material of animal and vegetable origin. First formed in deep sedimentary beds, petroleum later migrated to its present position in porous underground rocks. Petroleum occurs as either a liquid, a gas, or a combination of both. Occasional deposits elevated during the formation of mountain ranges, have been exposed by erosion to form tar (sometimes called pitch) deposits, and some of these have been known and used throughout recorded history. Other near-surface deposits of liquid petroleum seep slowly to the surface through natural fractures and fissures in the overlying rock, often aided by erosion or weathering. Accumulations from these oil seeps, called rock oil, were used commercially in the early 19th century. The vast majority of petroleum deposits, however, lie in natural rock at depths from 150 to 7.600 metres (500 to 25.000 feet) below the surface of the ground. The petroleum deposits, or reservoirs, are prevented from migrating upward by intervening layers of dense rock. As a general rule, the deeper deposits have higher internal pressures and contain greater quantities of the gaseous hydrocarbons.

In order to create a petroleum trap or reservoir, a porous rock (one capable of containing liquids), such as sandstone or limestone, must be surrounded on the top and sides by nonporous rock, such as shale. In such an event, either gaseous or liquid petroleum, which is less dense, than the always-present water, may be trapped in the top portion of the porous formation.

Since petroleum reservoirs are the result of an accumulation of liquid or gas in rocks originally containing water, there will always be some water left in the reservoir. Water production often accompanies the production of oil and gas.

When it was discovered in the 19th century that rock oil could yield a distilled product (kerosene) suitable for lanterns, sources of this oil were eagerly sought. It is now generally agreed that the first well drilled specifically to find petroleum was that of one Col. Edwin Drake in Titusville, Pennsylvania, in 1859. The success of this well, drilled close to an oil seep, led to further drilling in the same vicinity and soon to exploration elsewhere. The growing demand for petroleum products led quickly to oil wells not only in the United States but also in other countries. By the last quarter of the 20th century, there were approximately 600.000 producing oil wells in more than 100 different countries. Oil is produced in every continent except Antarctica.

Because of the widespread distribution of petroleum reservoirs, it was possible for new discoveries to be made at a rapid rate through the 1950s. As one result, there was little incentive for the development of efficient production techniques. Because little use had been found for the natural gas produced along with the crude oil, the gas often was burned at the wells. Such wasteful practices were gradually halted, partly by the increasing difficulty of finding new petroleum reservoirs and partly by the increased uses found for natural gas. New engineering methods led to an economically optimum recover)' from each reservoir. These methods often were based on the injection of some less expensive fluid, such as water, to force additional petroleum into the producing wells.

As the value of the petroleum produced reached impres­sive proportions, governmental agencies in every producing area sought to prevent wasteful exploitation.