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by Dmitry FYODOROV, Dr. Sc. (Geol. & Mineral.), GEON Center of Regional Geophysical and Geoecological Studies, RF Ministry of Natural Resources
The oil and gas deposits of the Caspian have been common knowledge practically from time immemorial. The ancient Greek biographer and historian Plutarch wrote that on his approach to the Girkana Gulf "... Alexander the Great, King of Macedon, was struck by the sight of a chasm... which was spitting out fire and torrents of oil flowing into a nearby lake." Two and a half centuries later, in the mid-20th century, people started for the first time in the world petroleum extraction on an industrial scale from sea platforms located on the Neftyanye Kamni (Oil Rocks) far from shore. But the risks involved transpired soon thereafter when one such platform off the Apsheron Peninsula was swept away by a storm together with a team of workmen(of foreman Kaverochkin) who manned the site.
CROSSROADS OF INTERESTS
The Caspian-the largest inland sea in the world (some 1,200 km long and up to 320 km across)-contains what experts call unique biota. Its main treasures, however, are massive deposits of hydrocarbons (which have been confirmed by the latest prospecting in various geological structures). Their strategic value consists in their most advantageous location: on the one side-between the main oil and gas markets of Europe and Asia, and, on the other-between the main suppliers of these raws (Near East and Russia).
In view of this situation two projects have been worked out of what are called transregional oil and gas pipelines of large diameter. One will run across the sea from Tengiz (big oil field on the north-eastern shore) to Baku and then stretch across the Transcaucasus to the Turkish port of Jeikhan on the Mediterranean. The second pipeline will start at the Shatlyk field in Eastern Turkmenistan and run across the Caspian, then through the territory of Azerbaijan and Georgia, and on to the Turkish port of Erzerum.
Needless to say, projects of this magnitude involve the economic interests of Russia to say nothing of their potential ecological safety problems. At the present stage of the general situation there are some unsettled legal problems linked with the status of the Caspian with respect to the five states on its shores (Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan) not to mention other matters of no lesser importance. These concern the volumes of the local resources (both proven and expected), and the ecological safety of the proposed oil and gas pipelines which will be located within a closed body of water known for its high seismicity, undersea volcanoes and landslides.
Preparatory work is proceeding most actively on the Azerbaijan section of the Caspian shelf. The prognosticated oil (and condensate) resources in this region amount to 2.3 bin tons and 3.8 bin tons of gas. Taking part in the associated contracts are a total of 28 companies from the United States, Great Britain, Norway, France, Italy, Japan and other countries including such leaders as BP Amoco, Chevron, Exxon Mobil and Total Fina Elf. The only Russian player is LUKoil whose share in the two leading projects - Azeri-Chigar-Gyuneshli and Shakh-Deniz-is limited to 10 percent. That means that this country's share of oil and gas supplied through the two pipelines across the Caspian will not be very substantial as compared with the scale of the ecological threat to
the unique local biota, including shallow northern spawning grounds.
The water area, or aquatory, of the Caspian covers parts of four sedimentary basins- North Caspian, North Ustyurt, Mid-Caspian and South Caspian ones-with the most promising deposits of oil and gas.
Within the boundaries of the sea, the North Caspian one occupies the southernmost part of the Precaspian border depression of the East-European platform. Its oil and gas resources are closely linked with the presence of three sedimentary formations: subsalt, salt-bearing and supra-salt ones. In the first case the geological prospecting objectives are carbonate massifs of the Permian-Carboniferous-Devonian age (285- 410 min years) located at the depth of 3.5-6 km; with the bulk of the deposits gravitating to the Mid-Carboniferous (350 min years).
The typical examples of the giant local carbohydrates deposits in the local conditions are the Astrakhan sulfuric-gas-condensate one and the Tengiz oil field. The former is located on the northern coast and linked with an elongated (more than 100 km) flattened platform. The height of the deposit is not great-of about 200 m, but due to its large area it contains giant volumes of gas (circa 4,000 bln m 3 ) as well as oil and condensate (total of up to 2 bin tons). The sum of the acid components in the gas- hydrogen sulfide and carbon dioxide-approaches 50 percent.
The picture is different at the Tengiz field discovered in the limestones of the Carboniferous-Devonian age in the north-eastern coastal region. This is a typical buried uplift on a relatively small area, but with the height of several kilometers. According to current estimates the thickness of its oil-bearing part, not yet fully stripped, approaches 3 km. The geological oil reserves are estimated at 2.9-3.2 bin tons and the recoverable, or extractable ones at 0.9-1.3 bin tons. The expected output of the Tengiz field in 2001 is 12 min tons and in the following years and in connection with the filling of the Aktau-Atyrau-Astrakhan-Novorossiisk pipeline the production can be brought up to 32 min tons a year.
There are grounds to believe that in the shallow zone between the two aforesaid giant deposits there is a group of some similar major oil traps, overlapped with a salt- bearing sealing cap. These include Morskoy Tengiz, Eastern and Western Kashagan and several others chiefly gravitating towards the Kazakhstan sector of the sea. For example, the OKJOC Company in Eastern Kashagan drilled a prospecting well to a depth of 4,500 m and in probing subsalt limestones struck oil and gas with the daily output of 600 tons and 200,000 m 3respectively. A second well-in West Kashagan-struck a similar carbonate reservoir.
Another promising oil and gas basin is the Mid-Caspian one which occu-
pies the deepest part of a protracted sub-latitude zone between two oil and gas-bearing provinces located on dry land (Ciscaucasian in the West and the Mangyshlak in the East), Here, like in the North Caspian basin rather big deposits have been identified, stretching far from shore into the sea: the Dmitrievsk on the Dagestan shelf and the West-Karazhanbassk on the Kazakhstan side. In respect of geodynamics the central zone of the Caspian is within the borders of the Skithian-Turan platform which acts as a buffer between the very mobile Alpine-Himalayan folding belt in the south and the rigid East-European craton in the north. Because of that the south-western part of the oil-bearing basin under review which adheres to the Alpine-Himalayan belt, features high seismicity and active faults of the earth crust. The main of them are-the submeridional West Caspian, sub-latitudinal Central Caspian and the diagonal one of Makhachkala-Krasnovodsk. It should be noted that all of these active geological structures are located right on the path of the projected transregional oil pipeline ofTengiz-Baku-Jeikhan.
The base of the sedimentary cover in the Mid-Caspian basin are moderately folded and metamorphosed Paleozoic sediments-at the depth from 2.5 km in the northern part and down to 10-11 km in the contours of the North Apsheron basin. At the same time in the South Caspian and Near-Caspian depressions, bordering on the Mid- Caspian, the base of the sedimentary cover lies much deeper-at 20-25 km. Thus the Middle Caspian-submerged with respect to the Ciscaucasian and Mangyshlak provinces and elevated with respect to the North Caspian and South Caspian basins-is tectonically the biggest saddle of all. And it should be noted that similar structural- tectonic elements like the Ludlovsky saddle in the Barents Sea* or the Stavropol arch in the Ciscaucasus region are distinguished by favourable conditions for the formation of big oil deposits, like the Stokmanovsky one in the Barents Sea or the North Stavropol field.
A large section of the Middle and North Caspian is under Russian administration. The results of offshore drilling on the Khvalynskaya and Shirotnaya structures, started recently by the LUKoil Company, give grounds to expect that sufficiently large multilayer oil and gas deposits are likely to be found there (the so-called Northern Territories). For example, at the Shirotnaya site the flow of oil from the carbonate rocks of the Lower Cretaceous exceeded 350 tons a day, and that of gas with condensate from the Mid-Jurassic sandstones-1.5 min m 3 .
The most promising for the identification of major fields in the Mid-Caspian basin are areas where the southern slope of the Karpinsky Bar
* See'. Ye. Velikhov et al., "Gas, Oil and Ice", Science in Russia, No. 3,1994.- Ed.
(Russian coast) and the Buzachinsky Region (Kazakhstan jurisdiction) extend into the sea, and also the Yalama-Samursky arch located under the bottom of the Caspian near the border between Russia and Azerbaijan.
The next oil-bearing region on our list is the South Caspian one. Its main part, linked with a deeply submerged plate of the same name, is covered with water. This is a typical marine basin, but being part of the active Alpine-Himalayan folded belt, it also has some features of an intermontane depression flanked on three sides by the mountain systems of the Caucasus and Kopetdag, and on the fourth side by a mountain-folded chain of undersea structures of the Apsheron-Balkhan tectonic threshold (zone of collision of the South Caspian and Scythian-Turan plates). The leading role in this basin belongs to the Mid-Pleocene deposits (25 min years) and formations in the ancient deltas of the Volga, Samur, Kura and Amu-Darya which contain thick strata of turbidites (laminated sands, alevrites and clays).
Since the start of the operation some 1.5 bin tons of oil and gas (in oil equivalent) have been extracted here, which, in expert opinion, is less than one tenth of the potential resources. Developed so far, however, are mainly what we call the "golden belt" deposits gravitating towards the Apsheron-Balkhan threshold. The estimated extractable resources of oil at the biggest local deposit-Azeri-Chigar-Gyuneshli (developed by an international consortium) are currently estimated at 800 min tons for oil and 150 min tons for gas.
According to expert forecasts, some even bigger fields are located on the edge of the Bakinsky archipelago and a deep-sea basin. Identified there already is the Shakh- Deniz deposit where gas reserves amount to 1,400 bin m 3 , and those of condensate-320 min tons. Within the borders of this area the depth of the sea rapidly increases from north to south-from 50 to 550 m, and gas deposits with condensate have been struck at greater depths but in very young Pleocene formations. In one of the wells they obtain from the depths of 6,225-6,289 m gas at the rate of 1.5 min m 3 per day, and condensate of about 400 tons. In another well, located 6 km to the south, the yield from depths of 5.730-5.815 m was respectively 1.8 min m 3 and 520-540 tons. On the strength of these data there is a much greater probability of discovering considerable oil and gas deposits in the major structures of Apsheron and Nakhichevan which are also located on the slope of the marine deep- sea part of the
South Caspian basin. According to our assessments, it accounts for nearly one half of the potential oil and gas resources in the whole of the Caspian region; and the share of the proven resources is also the highest here.
The other half is equally divided between the North Caspian (its marine part) and Mid-Caspian basins.
So, the oil and gas potential of the whole water area is linked with a broad stratigraphic range (periods of formation) of oil and gas deposits of industrial size- from post-Pleocene to Devonian (20-400 min years). Predominating in various parts of the region are different complexes: in the north-Devonian-Carboniferous, in the middle part-Jurassic-Cretaceous, and in the south-Pleocene-Quatemary. Proved in these deposits all in all by the beginning of the year 2001 were 40 deposits of oil and gas: 30 in the Azerbaijanian part of the Caspian, 5-in the Turkmenian, 3-in Russian and 2-in the Kazakhstan ones.
Since in all of the newly discovered structures, where prospecting drilling has been started over the past two to three years, experts have struck rich deposits, one can regard the oil-and gas-bearing capacity of the Caspian as being very high. At the same time the share of off-shore resources ready for commercial exploitation is still relatively small, and there is no special need to ferry the output of dryland fields across the sea.
The formation of major oil and gas deposits on the Caspian has been linked in most cases with the current geodynamic regime of geological bowels or their active past. The subduction of one lithospheric plate under the other, their rapid subsidence with the formation of the shelf and deep troughs or basins and the initial stage of orogenesis-all of the geodynamic processes conducive to the accumulation of oil and gas did take place in this region. As was pointed out, the Caspian "megabasin" is superimposed on the border region of the Alpine-Himalayan folded belt and the Eurasian platform, and this accounts for the unstable condition of the lithosphere in this region. These things manifest themselves today in the movements of its blocks and seismicity, mud volcanism, undersea and ground earth slides (the latest and rather big one, which ruined buildings and installations, occurred in Baku in June, 2000). Seismicity manifests itself most often in the form of pulsed scatter of elastic energy of geological structures on the border of major lithospheric blocks and the faults separating them. Of the latter the longest ones match the points of collisions of the South Caspian plate with the Iranian one in the south and the Scythian-Turan one in the north. The most active in the latter case were the Central Caspian and Makhachkala-Krasnovodsk rift systems. In comparison with them the northernmost area of "ancient" rifts, separating the Near-Caspian border depression from the Scythian-Turan plate, is relatively "passive".
In keeping with this generalized structural diagram of the region, the number of quake epicenters increases from north to south-from the Mid-Caspian basin to the South Caspian, and the magnitudes of underground shocks vary from 3.5 to 7. In the marine part of the Caspian there occurred from 1983 to the year 2000 close upon 30 perceptible tremors and all of them close to places of planned pipeline construction. The last two and relatively strong seismic events took place in the late 2000. The first with the magnitude of 6.6 and epicenter intensity of up to 7.5 points occurred in the sea near Apsheron (it was felt also in the north of the region-in Astrakhan, at 4 points strength). The second occurred across the sea, near Nebitdag, with the magnitude of 7.4 and epicenter intensity of 8 to 9 points (5 points in Astrakhan).
It follows from the above that the development of the oil and gas potential of the Caspian calls for the preliminary studies of its complicated geodynamics. The proposed main oil and gas pipelines like those from Aktau to Baku, Nebitdag-Baku, Baku-Supsa, Supsa-Ankara and Sup-sa-Jeikhan, will be crossing zones of high seismic activity or running through them. Naturally enough, putting local oil and gas deposits to industrial uses and making them available to users is a task for the future. That, however, does not eliminate the need for coordinated and systemic preliminary studies in the region. These should include in-depth seismic soundings along the proposed routes of the pipelines, monitoring of changes of stresses in the elastic- brittle layer of the lithosphere in most hazardous areas, especially those where large volumes of fluids (oil, gas, condensate, water) are to be extracted over long periods of time.
The word "coordinated" studies occurred in the previous paragraph not by chance. On March 1, 2001 there was a meeting in the Kazakhstan capital Astana of representatives of the host country, Azerbaijan, Georgia, Turkey and the United States at which they signed a Memorandum of mutual understanding on the project of oil transportation along the route of Aktau-Baku -Tbilisi-Jeikhan. Regrettably, the list of the participants did not include such near-Caspian states as Russia, Turkmenistan and Iran. And this is despite the fact that the plans of building high-pressure oil and gas pipelines of large diameter across the Caspian involve the interests of all countries of the region. This being so, projects of this kind should be submitted to preliminary and independent geoecological expert assessment by the parties concerned.
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