Oil field

Under an oil field is defined as a region under which a mineral oil deposit is located. Areas of developed oil fields are characterized by the most extensive facilities for production, treatment, processing and transportation of oil. Worldwide there are about 43,000 known oil fields. About 94 % of the quantities of oil previously found worldwide but are concentrated in only about 1,500 oil fields.

The expansion of the oil fields ranges from a few acres to several thousand square kilometers. So the world's most productive oil field Ghawar in Saudi Arabia extends over nearly 3000 square kilometers.

Approximately 22 % of world oil reserves ( in Europe 90%) are located under seas and are exploiting only with great effort. Around one third of the current global oil production takes place "offshore".

Geology

In a natural oil reservoir, the oil often under high pressure treated - often, with salt water, and natural gas - in porous rocks, mostly sandstone or Riffkalkstein, which is up by impermeable layers, such as from shale or fine-grained limestone ( micrite ), sealed.

Petroleum can only be won when the oil -bearing rock, the so-called reservoir rock, a certain Nutzporosität has, in such a way that existing in the rock pores are interconnected. This is known as pore interconnectivity. This results in a certain permeability of the reservoir rock, called permeability, which is measured in Darcy (D). The usual for oil reservoirs values ​​for the permeability ranging from 5 to 2000 mD ( millidarcy ). The ratio of the pore volume to that of the solid support of the oil rock, the porosity is usually in a range of 5 to 30%.

The oil reservoirs are the end result of a long development process. The result is the so-called oil in the source rock, which consists of relatively dense and very fine-grained rock types, such as marl or shale. An entity known as migration migration movement, first from the mother rock out, followed by porous layers of rock through it, resulting in a concentration of points ( called traps ), where a progression of the migration process is inhibited by the geological conditions. We distinguish the following types of cases:

• Hydrodynamic traps, in which water flows impede the migration of petroleum in the ground
• Combination traps when more of the above processes were effective

In most cases, there are combination traps before with dominance of one type.

The vast majority of previously known petroleum deposits are located in a depth range of 500 to 3000 m. Since the formation of oil requires relatively high temperatures (60 ° C to 150 ° C) and pressure, it takes place at a depth of 1500 to 3000 m primarily. By migrating from these deep rock layers but there are numerous deposits shallower. Encircled with crude oil is also directly on the surface, but almost always only in small amounts.

The oil-bearing layer is powerful in most deposits a few meters. Deposits particularly productive oil fields come over widths of 50 to 100 m. Only in a few cases, the thickness up to several 100 meters. The great fertility of many oil fields based rather that several - are stored in the oil-bearing layers alternating with oil-free layers one above the other, with the depth range can extend to over 2000 m - up to 20.

Prospecting and development

See also: prospecting and extraction of oil

Feeding operation

Oil is produced from so-called probes, which can be accessed at Sea oil rigs and production platforms from special. Funding is provided by a separate string of pipe is introduced ( called casing ) in the lined through a pipe hole.

The distances of the probes to each other at an oil field depends on the thickness and number of oil-bearing layer (s ) and the permeability of the reservoir rock (so-called permeability). Previously, the probes were set very close in many oil fields, which had an uneven exploitation and rapid depletion of reserves result. Today it seeks to take out as much oil as water can flow from the surrounding soil layers. This so-called Water power is the most efficient natural drive mechanism in most cases and provides a uniform and constant over many years of exploitation of the oil reservoir.

In the newly developed oil fields at first the reservoir pressure is sometimes so high that some of the oil - there are usually also low-boiling organic compounds - by itself rises in sufficient quantity. This is called Eruptivförderung. A fading and low reservoir pressure usually deep pumps of various designs are used. Preferably, in low-lying deposits frequently and the gas lifts to use. Here is the associated gas that often occurs with the surface with the crude oil is separated and pressed into the cavity between the oil string and well casing. About valves in the tube of the delivery line, the gas passes from the annular space in the production string. The rising gas bubbles float as a result the oil upward.

Previously, the image of the oil fields was dominated by so-called winding towers. These served the maintenance of the probes. At regular intervals, the production string must be removed from the wellbore to fix damage caused by corrosion or clogging due to sand contamination. When using a rod deep pump, it is also necessary to set the linkage and the pump piston, which are subject to considerable mechanical wear regularly serviced. In order to do a winch was attached to the tip of the shaft towers. Today the stationary winding towers have almost disappeared. Instead, mobile, mounted on trucks telescopically extendable towers with a winch to probe treatment used.

Because the oil is stored in a mineral ' sponge ', the feed rate is not over the entire period of constant, but increases gradually from. The oil seeps through the mineral bedrock or pressed through reinforced by technically elevated pressure. The farther the distance to the hole, the longer is the way and the time needed for this. Addition, the different proportions of oil behave differently here. The volatile and thin liquid components migrate through the rock generally faster than the non- volatile and semi- liquid. This is similar to the behavior of the mobile phase in liquid chromatography. With ongoing funding so that the oil is recovered Anyway thicker and heavier, and the amount of energy required to grow to the extent to which empties the reservoir.

A decisive influence on the flow rate also has the dilution. In the deeper layers of oil-containing reservoir rock, and waters of the primeval ocean earlier is stored, which penetrates deeper into those areas from which the oil was previously deducted. Thus, the water content of the material to be conveyed is steadily increasing. The promotion will be considered but generally even at a dilution rate of well over 90 % more than profitable. So was in Oklahoma, the average net yield of oil per probe in 2006 only just over two barrels, equivalent to about 0.25 tons of crude oil.

The accompanying water containing environmentally harmful salts and sulfur compounds, mostly separated even at the oil field in special plants from oil and pumped back through too strongly diluted probes in the lower lying areas of the oil field back into the reservoir, so as to obtain reservoir pressure as high as possible. The pumping water and other tools into a reservoir to increase the yield is referred to as flooding.

At the end of some of the oil remains in the field, which due to low permeability ( permeability ) of the reservoir rock can not be profitably mobilize. In most cases, this accounts for over 40% of the reservoir contents. The exploitation of an oil field usually extends over a period of 20 to 50 years.

At the end of the use of an oil field is the most superimposed on the associated gas cap, which was useful for the preservation of the reservoir pressure so far degraded. No longer required holes are cleaned of oil residues and with Betonpropfen in the recovery zone (s ) and sections closed it. The uppermost part of the pipe string ( from 2.5 to 5 m ) is then separated and removed and transported back to the area in the original state.

Records

The area of ​​income from oil fields have as a result of the diversity of geological structure on extreme differences. Most - simply structured - deposits show an average oil yield of 500 to 3000 tons per hectare. As productive designated oil fields come on yields per hectare 10000-40000 tons. The highest yields per hectare were at the - now largely exhausted - oil fields in Baku / Azerbaijan and Ploieşti / Romania, where you could win oil per hectare to over 300,000 tons.

The most productive oil well in history was the 1916 and drilled out of control probe Cerro Azul 4 in still oil-rich Chicontepec Basin near the west coast of Mexico. On February 10, 1916 were encountered in only 546 m depth initially on gas. The high pressure of the gas pulled away a part of the drilling rig, whereby it was not possible to close the borehole. After seven hours, the escaping from the borehole gas jet turned black. In the following 9 days, about 300,000 tons of crude oil occurred in an up to 300 m high fountain out of the hole and turned the area into a sea of ​​oil further. It finally managed to put a valve on the well head. By 1932, the probe yielded about 13 million tonnes of oil when suddenly broke through the water and the oil recovery finished.

The largest oil fields

Worldwide, sorted by size:

The fields represent 12% of the world's known reserves. (2007, Source: Black prospects, articles in the journal EUR, Issue 8, 2007, p 14)

• Carioca, Brazil (not yet developed)

Gallery

Winding towers in Summerland oil field near Santa Barbara, California, about 1915.

One of the most productive oil fields in Europe Moreni in Ploiesti / Romania about 1920.

In small oil fields is often promoted a modest amount of only one probe - here Kematen, Upper Austria, since 1967, about 25,000 tons.

The oil field Zistersdorf - Gaiselberg is barely 2 km ². However, approximately 5 million tons of oil were recovered here since 1937.

Because of the existing infrastructure (roads, power lines) to oil fields are well suited for wind farms.

In the area, the largest oil field in Central Europe matzo Auersthal the myriad funding bodies are scattered in the landscape.

In developed more recently, oil fields, the funding of central drill sites is carried out.