Among important historical events of XXI century a special role is attributed to exploration and use of various types of primary energy resources. If in XX century B.C. 70-80% of energy used has been muscle force, in XV century - wood, earlier in XX century - coal, then at the end of XX century various types of primary energy - coal, oil, gas and nuclear are being used almost in equal proportions. From the tendency existing today, we can forecast considerable reduction of consumption of coal, but less consumption of oil and nuclear energy and increase of consumption of gas and alternative energy types (sun, wind, floods, geothermal power, etc.) (fig. 1).

Azerbaijan has played a significant role in formation of primary energy consumption structure in the world. According to the number of mud volcanoes and volume of hydrocarbon gas discharged to the atmosphere, quantity of oil produced from every sq. m. of field area this original natural museum has no its analogy on the world.

Oil and gas production history of Azerbaijan in X century is marked by three periods of maximums: I - beginning of the century, II - 1940's and III - 1970's. In the beginning of the century 10 million tons of oil was produced in Azerbaijan. Though this is not too high figure as compared to current production rates, it constituted half of total quantity of oil produced in the world at that time. During the second stage, the use of Azerbaijan oil in fronts of the World War II put an end of fascism in European continent. The third oil and gas boom was associated with discovery of offshore oil fields and gas condensate deposits in productive series. The beginning of XXI century is marked with new considerable increase of oil and gas production in Azerbaijan.

In XX century 1.5 billion tons of oil and 500 billion m³ of gas have been produced in Azerbaijan. SOCAR has in its possession 181 billion m³ of commercial (A, B, C₁) gas and 2336 billion m³ of gas, including developed, perspective and predicted reserves. These gas reserves are naturally distributed in productive series section and along the area. The largest gas accumulations are confined to lower parts of Balakhansk suite and the suites in lower part of productive series. Subsequent increase of gas content of fields and transition from fields with solved oil to fields with gas cap is observed over the area in the direction of subsided depression zones of productive series which have gone through negative movements during its geological development, and transition to gas condensate bearing deposits is observed in subsidence zones. The basic gas reserves owe to the latter for its existence. This regularity of reserve distribution is well traced in the map of gas content of productive series (fig. 2) and in more details in profiles built across Balakhany- Sabunchu-Ramany, Surakhany, Garachukhur, Zykh, Gumadasy, Bakhar and Duvanny, Kyanizadagh, Sangachal-Duvanny, Bulla-deniz fields (fig. 3), as well as the deposits of VIII horizon in Western Absheron-Ateshgah, Lokbatan, Puta-Gushkhana, Gushkhana and Garadagh fields (fig. 4). All the material given as an example show transition from oil to oil ad gas and gas condensate bearing deposits towards subsidence of structures.

The natural variation of gas saturation of productive series correlates well with geochemical and thermodynamic properties. The maps built for variation of hydrocarbon gas composition show percentage increase of methane content for deposits in productive (the western edge) and red rock (the eastern edge) series in the direction of subsidence of layers (fig. 5) .Variation of the content of heavy hydrocarbon total is different for the western and the eastern edges of the South Caspian depression. In the first case the content of methane homologue increases in the direction of subsidence of layers, and in the second case it decreases.

Brief description given here for geological, geochemical and thermodynamic features of distribution of oil and gas condensate bearing fields in productive series and which is also characteristics for red series of Turkmenia, allowed to extrapolate these regularities within the whole water area of the southern depression of the Caspian Sea with various gaseous and fluid hydrocarbon ratios. The prospective zones with various gaseous and fluid hydrocarbon ratios are conventionally indicated in fig. 6.

In the east of the South Caspian depression a zone with prevailing accumulation of gaseous hydrocarbon in gas condensate and gas bearing beds is identified. Existence of large and medium capacity fields is predicted here.

Specific feature of this zone is that the fields that we think exist here may contain, in addition to large quantities of gas, also corresponding quantity of hydrocarbon fluid in the form of gas condensate and oil. It is known that usually transition from oil to gas fields is accompanied with increase of methane concentrate and decrease in percentage of heavy hydrocarbon total. This is what we observe in the eastern edge of the depression. In contrast to this, in the western edge of the depression, as it has already been mentioned above, increase of methane concentrate and its heavy homologues occurs in the direction of subsidence zone of productive series. This fact along with other data, including carbon isotope, allow us to state that the subsidence zone identified by us is the focal place where oil and gas is generated out of fluid and gaseous hydrocarbon. That is why the gas condensate bearing fluids, existence of which we forecast, will also contain reserves of oil in the form of large oil edgings and individual oil horizons. Increase of quality of hydrocarbon fluids parallel to increase of gas reserves is also observed in the gas condensate bearing fields that are under development today. Increase of condensate content and oil with increase of gas reserves is also observed.

The above-mentioned two zones are framed from west, east and north with a zone of distribution of oil fields containing mainly gas solved in oil and gas caps.

In the south of Azerbaijan sector of the Caspian Sea in the east of its Turkmenian sector distribution of oil fields with various, including large quantity of gas is suspected.

The above-mentioned promising oil and gas reserves of Azerbaijan are, mainly, confined to offshore fields, the exploitation of which is connected with certain difficulties. However, the existing data and forecasted made for XXI century allow us to state that hydrocarbon production in the world will require their development.

The promising fields on the Caspian are located at 700-1000 m depth. Currently SOCAR drills to depth no higher than 150-200 m whereas the world is aware of drilling practice to much higher depths. For example, the Brazilian Oil Company "PetroBraz" has drilled in the Atlantic Ocean wells as deep as 1420 m, 1709 m and 1853 m. This allow us to state that from the point of view of technical support exploitation of the fields in the Caspian is feasible enough.

Some scientists hold the opinion that in the beginning of XXI century oil and gas production in the world will reach its peak value and start falling down in the well-known oil and gas bearing provinces. This data were published by David Brown in "Explorer" newspaper issued by American Association of Petroleum Geologists based on the material taken from presentation of Richard A. Startman's and A.S. Al-Jarri's from Texas University. Similar results are also obvious in the graphic (fig. 7) published by Alian Perrodon, Jean Laherrere and Colin Campbell, international experts on oil and gas production. Thus, in XXI century considerable reduction of hydrocarbon production and exhaustion of fields which are currently in exploitation in Russia, USA, the Persian Gulf, etc. is predicted. On this background it becomes obvious that the use of large energy potential of the Caspian region, Azerbaijan, in particular, is requirement of life.

Three curves are given in fig. 8 which describe exploration speed and development of primary hydrocarbon resources: stands of old oil and gas bearing regions (1) , for regions with intermediate conditions (2), for newly discovered fields (3) . Because the oil and gas reservoirs in the western and eastern edges of the South Caspian depression have been in use for many years and there still remain hundreds of structures in its water area that haven't been drilled yet, the 2^nd curve is more adequate for Azerbaijan's promising offshore structures. According to this curve, the hydrocarbon fields, the existence of which we forecast, can be developed within 80 years, i.e. to the end of XXI century. It is clear that financial and technical support of required for this purpose. With favourable conditions and high technological development in oil industry in XXI century, the terms of exploitation of these fields can be considerably reduced to 50-60 years.

Taking into Azerbaijan's needs for hydrocarbon fuel and crude which will constitute only small portion of its reserves and production, there appears a serious problem connected with its sale to other countries and, in the first place, to Turkey and Europe. This requires constriction of corresponding transportation system, oil and gas pipelines, in particular.