Natural bitumens

NATURAL BITUMENS (EN: bitumen; DE: naturliche Bitumina; FR: bitumes naturels, bitumes mineraux; ES: betumenes naturales; RU: битумы природные) are the useful minerals of the organic origin with the primary hydrocarbon basis, which are embedded underground in the solid, viscous, and viscous-plastic states. From the genetic point of view, they classify as the natural bitumens the petroleum, combustible natural gases, gas condensate, and also the natural derivatives of petroleum (malthas, asphalts, asphaltites, kerites, humic kerites, ozokerites, anthraxolites, and others) and their analogues (naphthoids).

Natural bitumens were used at the Middle East during the 3rd millennium BC as the binding building material, and for the embalming (Ancient Egypt). Later, natural bitumens were episodically used within many countries for the construction, medicine, military craft, as varnishes, and so on. During the 15th century, there were built within Peru by the Incas the roads with the coating, which was made of the natural bitumens. During the end of the 18th century, there was attempted the commercial development of the natural bitumens within Athabasca (Canada). During the middle of the 19th century, there have been built the first asphaltic pavements within the Paris city and London city, using the natural bitumens from the field within Cecelia (France), and during the 1870-80, the pavements have been built within the series of the USA cities, using the asphalts from the Trinidad and Bermuda fields. During the start of the 20th century, they intensively develop the fields of the natural bitumens within the USA, Italy, Trinidad, Germany, France, Venezuela. Within the USSR, the asphaltic bitumens were extracted during the 30-50-ies within the Volga region (Pervomaiskoe, Shugurovskoe, Sadkinskoe, and other fields), within the Western Kazakhstan (Munaily Mola, Ak-Chii, and others), within Georgia (Natanebskoe), within the Komi ASSR (Izhemskoe), and within other regions, the ozokerites were extracted within the Carpathian region (Borislavskoe, Dzvinyachskoe, and others), and within the Central Asia (Shor-Su, and others). By the start of the 80-ies, there are operated only the Sadkinskoe and Borislavskoe fields. The prospects for the significant expansion of the volumes of extraction of the natural bitumens are associated with the mastering and perfecting of the process for the industrial obtainment of the crude petroleum from them (see the "Hydrogenation" article).

Natural bitumens consist of the high-molecular-weight hydrocarbons and heteroatomic (oxygenic, sulfurous, nitrogenous, metal-containing) compounds. The physical-chemical properties of the natural bitumens are: the consistency, from viscous-liquid (maltha) to loose (humic kerites); the density is respectively from 965 to 1500 kilograms per cubic metre; the temperature of softening is from 35 degrees Celsius (malthas) to non-melting (kerites, anthraxolites, humic kerites); the solubility within chloroform is from 100% (malthas, asphalts) to non-soluble (anthraxolites). They determine the classification boundaries for the soluble natural bitumens according to the content of the oils: 65-40% within malthas, 40-25% within asphalts, 25-5% within asphaltites; for the non-soluble bitumens, according to the parameters of the elemental composition, and according to the optical data. For the certain varieties of the asphaltic natural bitumens, there is characteristic the generality by the sulfur 10-15% or more (thiokerites, quisqueites) and metals (V, Ni, U, Co, Mo, Rb, Ge, and others). There are known the industrial vanadium-bitumen deposits (for example, within Peru, with the content within the ash of up to 65% of V2O5 and 7.5% of NiO), uranium-bitumen deposits (on the Colorado plateau, within the USA), and others. For the series of the fields, there is characteristic the existence of the depositions with natural bitumens, which are various in composition (for example, the ozokerites and malthas, asphalts and kerites, and others).

The elemental composition (C, H, O, S, N) is determined by the semi-micro and macro methods, by the burning; the metals within the bitumens are determined by the methods of the colorimetry, spectroscopy, neutron activation, and others, while the group composition is determined by the methods of the ascending chromatography and others. The study of the non-soluble and non-melting varieties of the solid natural bitumens is performed by the infrared spectroscopy (the diagnostics of the chemical structure of the substance), and by the methods of the coal-petrographic researches (the determination of the reflective ability and refractive index). For the certain fields of the usage for the natural bitumens (for example, within the road construction), there are determined the penetration, temperature of the melting point, elongation, adhesion, cohesion, and so on.

The natural bitumens form themselves as the result of these processes: a) the biochemical and chemical oxidation of the petroleums within the zone of the supergenesis, with the forming of the series of the asphaltic natural bitumens (maltha, asphalt, asphaltite, oxokerite, humic kerite); b) the concentration of the asphaltic-resinous substances on the account of the disturbance for the equilibrium state within the colloidal system of the petroleum, with the emergence of the asphalts, asphaltites, less often malthas; c) the natural de-asphalting of the petroleums within the depositions by the gas or light methane hydrocarbons, with the forming of the solid natural bitumens, namely, asphaltenites (from asphalt to kerites); d) the thermal metamorphism (contact or hydrothermal) of the resinous petroleums and asphaltic natural bitumens, with the forming of the kerites, anthraxolites, petroleum coke; e) the differentiation of the highly paraffinic petroleums during the migration, with the emergence of the ozokerites; f) the destruction of the organic substance under the conditions of the contact and dynamic metamorphism, with the forming of the bitumens (naphthoids) of the asphaltic and paraffinic series, which are characterized by the properties of the petroleum bitumens.

The major reserves of the asphaltic natural bitumens (prevalently of the malthas) are confined to the monoclines, where they are controlled by the zones of thinning and non-conformal cutting of the regional petroleum-and-gas-bearing complexes of the sedimentary basins. The fields are situated on the outer edges of the Mesozoic-Cenozoic foredeeps, which are adjacent to the shields and vaults of the ancient cratons, and which are located within the zone of activity of the active infiltration. The largest ones of them (the reserves are in terms of the billion tonnes) are localized on the slopes of the Canada, Guiana and other shields, Olenek vault, where, together with the individual fields, have been traced the zones and belts (Canada, Orinoco) of the bitumen-accumulation. The fields of this type have formed themselves during the epochs of the intensive uplifts of the edge anteclises, when there were created the conditions for the ascending lateral migration of the petroleum from the adjacent downfolds, and for the oxidation of this petroleum by the sulfates and oxygen from the infiltration waters. The value of the losses for the initial reserves of petroleum on the account of the bitumen-forming process within such basins exceeds 95% (Western Canada, Eastern Venezuela). The depositions of the natural bitumens (layered) within the anticlinal structures are distributed prevalently within the limits of the eroded vaulted uplifts and paleo-uplifts within the regions of the ancient cratons (the field within the Anabar massif, within the Aldan shield, on the Siberian craton, within the "Zinchenko" paleo-vault, of the Middle Pechora paleo-uplift within the Timan-Pechora province), and also on the edges of the intra-cratonic depressions, and on the adjacent slopes of the large uplifts (the group of the fields within the Melekess depression, and of the Southern dome of the Tatar vault). The reserves of the individual depositions reach hundreds of million tonnes, of the zones with the bitumen accumulation reach several billion tonnes.

The veinous and stockwork bitumen accumulations form themselves on the pathways for the vertical migration of the hydrocarbons along the tectonic cracks, and are confined to the local ruptures on the petroleum-and-gas-bearing structures (Sadkinsk, Ivanovo, Borislav, and other deposits), to the zones of the regional ruptures within the advanced parts of the folded systems, and on the edges of the intermontane depressions and foredeeps (the system of the veins within the south-eastern part of Turkey, the fields of the Yuinta depression within the USA, and others). For example, the largest veinous bodies within Turkey (the Harbol, Avgamasya veins) reach the length of 3.5 kilometres, with the thickness of 20-80 metres, and may be traced to the depth of 500 metres. The covering depositions of the natural bitumens form themselves as the result of the subaerial metamorphose of the petroleums, which have flown themselves, these depositions attract themselves to the provinces of the Alpine folding, namely, to the internal edges of the foredeeps, and to the synclinal downfolds, are characterized by the high concentration of the bitumen with relatively small reserves. The individual depositions with the reserves of tens of million tonnes of the bitumen form the so-called asphaltic lakes (the Peach lake on the Trinidad island, Guanoko within the eastern Venezuela, Okha and Nutovo on the Sakhalin island).

The proven and promising geological reserves of the bitumens within the industrially developed capitalistic and developing countries are estimated at 580 billion tonnes, of which 71% are accounted for Canada, and 27% for Venezuela. The largest geological reserves of the natural bitumens are concentrated within Canada (413.8 billion cubic metres), Venezuela (approximately 159 billion cubic metres), and the USA (approximately 5.2 billion cubic metres). The largest deposits are: within Canada, Athabasca, Cold Lake, Peace River, Field Triangle, Uobaska; within Venezuela, Orinoco Belt (Suat - Morichal, Hobo, and others); within the USA, Peor Spring, Sunnyside, Tar Sand - Triangle; within Iraq, Koohe Mund. Therefore, there posssess the reserves of the natural bitumens Nigeria (0.84 billion cubic metres), Turkey (0.33 billion cubic metres), Madagascar (0.27 billion cubic metres).

Within the USSR, the total proven reserves are approximately 850 million cubic metres, the forecasted ones exceed 30 billion cubic metres, of which malthas account for approximately 53%, asphalts and asphaltites account for approximately 43%, ozokerites account for up to 0.5%. Approximately 90% of the forecasted reserves account for the eastern Siberia and the Ural-Volga region. The natural bitumens within the USSR are concentrated prevalently within the Paleozoic depositions (mainly within the Permian, Carboniferous, and Cambrian ones), and not more than 3-5% within the Mesozoic-Cenozoic ones. Within the eastern Siberia, there are known the fields of bitumens (for example, the Olenyek one); the group of the fields has been estimated within the Ural-Volga region (Ashalchinsk, Akansk, Aksubayevsk, Sugushlinsk, Mordovo-Karmalsk, Podlesnoe, Karasinsk, and others). Within the north-eastern part of the Timan-Pechora province, there exist the buried depositions of the bitumens (the Nyadeyyusk, Hosedayusk, Seremboysk fields). The accumulations of the bitumens have been identified also within the Western Kazakhstan, Central Asia, at the Caucasus, and within other regions.

The extraction of the natural bitumens is conducted by the open pit mining, underground mining, or underground borehole methods. The first method is effective for the small thickness of the overburden rocks (the ratio for the overburden stripping is up to 1). At the greater depths (which are counted within the first hundreds of the metres), they use the underground mining method. The underground borehole extraction of the viscous asphaltic natural bitumens is characterized by the thermal and other impacts onto the layer.

The worldwide extraction of the bitumens and highly viscous petroleums within the industrially developed and developing countries (1981) is: 103.5 million tonnes by the borehole method, and 9.8 million tonnes by the open pit mines (including 43.2 million tonnes within Venezuela, 17.2 million tonnes within the USA, 13 million tonnes within Canada).

The natural bitumens are the complex raw materials, mainly chemical and energetical. They obtain from the asphaltic bitumens the light synthetic petroleum and petroleum coke, the components of the motor fuel, and so on. The natural bitumens and the heavy highly bituminous petroleums are the sources of the sulphur, precious metals (V, Ni, Sb, Ge, U), and so on. Within the USSR, the generality by vanadium and nickel is characteristic for the fields of the natural bitumens within the certain regions of the Ural-Volga region, Western Kazakhstan, Central Asia, north-east of the European part of the USSR. The natural bitumens are used as the construction raw materials (road coatings, production of the soft roofing, asphaltite mastic, and so on), within the electrical industry (insulators, anti-corrosion coatings, and so on).