Chechnya sees potential for 'nontraditional' deposits
This article is a discussion of the state of the oil and gas industry in the Chechen Republic, the need for introduction of modern technology to revitalize it, and the potential for adding significant reserves by drilling to deeper formations.
It recounts the main stages of discovery of oil deposits in Middle Miocene, Cretaceous, and Upper Jurassic and delineates the prospects for future exploration of hydrocarbons required to increase oil and gas production on the territory of Chechen Republic in the peaceful time.
Introduction
An improvement of the economic and social prosperity of the people of the Chechen Republic is greatly related to recovery of the destroyed oil and gas industry and to increasing production and processing of crude hydrocarbons, the republic's main natural resource.
In spite of oil production declines in the 1980s-1990s, an objective analysis shows that the republic's natural resources are not exhausted. The economic destabilization after the Revolution of 1917, during World War II (1941-45), and the USSR breakdown influenced and are influencing the production of crude hydrocarbons. However, in some periods this influence was not so severe, and this allowed some increase in oil production.
Oil and gas history
Oil production from pits was known in the Chechen Republic since 1833, though it is obvious that this method is much older.
According to preserved data, the cumulative oil production amounted to only 53,983 tons for the period from 1833 to 1893.
In 1893, the first well 1/1 was drilled in Middle Miocene sandstone by a percussion drilling method to a depth of 134 m on the Starogroznenskaya area of the Grozny mountain ridge. For the first 15 days the well gave over 17,000 tons.
The second well 7/977 in 1895 penetrated the formation 1 at a depth of 140 m. The deliverability of this well was 16,000 tons/day (t/d). During 3 years 700,000 tons of oil were produced.
In 1912, exploration work revealed a unique, by its high oil content, Karagano-Chokrakean formation of the Novogroznenskoye (Oktyabrskoye) field near the Aldyn mountain ridge. Later, thanks to exploration work a commercial oil accumulation of Middle Miocene on Malgobekskaya (1933), Goragorskaya (1937), Oisungurskaya (1939), and some other areas of the Grozny oil and gas bearing province (OGBP) was proved.
The results of geophysical surveys played a significant role in studying the deep structure of the OGBP in the Chechen, Ingush, and Dagestan republics.
Since 1953 (it should be especially noted), mainly deep Mesozoic deposits were included in exploration work. The interest to their investigation grew when in 1956 a commercial oil inflow from fractured Upper Cretaceous limestone on the Karabulakskaya area was obtained (Well 16 output was 189 t/d).
Later, high prospects for oil in Upper Cretaceous deposits were proved in a regional plan, i.e., in areas confined to the Sunzhensky and Tersk mountain ridges and Alkhanchur Valley that separates the ridges.
These prospects were also proved by the discovery of a gas-condensate pool on the Benoiskaya area. Gas on the Datykhskaya area of the monocline of the northern slope of the Great Caucasus was recovered from Lower Cretaceous and Upper Jurassic.
The recent past
The further survey of Mesozoic deposits showed that the terrigenous-carbonate complex of Lower Cretaceous also differed by the presence of considerable commercial oil and gas accumulation.
Geophysical surveys allowed detailing of the deep tectonics of the front ridges and synclinal troughs, i.e., the Alkhanchurtskaya, Petropavlovskaya, and Priterechnaya seam zone of the joint of Tersk-Sunzhen dislocation with Epihercynian platform of Eastern Ciscaucasia.
This detailing was the basis for starting successful exploration work that led to the discovery of oil accumulations in Cretaceous formations, including structural satellites on the areas of Mineralnaya, Severo-Mineralnaya, Severo-Malgobekskaya, Severo-Bragunskaya, and others.
Oil inflows with considerable hydrogen sulfide content were obtained from Upper Jurassic and Lower Cretaceous structures in the Malgobekskaya, Zamankulskaya, and Starogroznenskaya areas, the exploration of which was limited by the lack of appropriate corrosion-resistent equipment.
Thus the discovery and development of high productive (up to 6,000 t/d) oil pools in Upper Cretaceous deposits of OGBP and flowing well operations created the possibility of quick growth of oil production in the Grozneft Co. with a production peak of 21.6 million tons/year in 1971.
By 1990, most of the oil and gas fields had entered a final stage of their development characterized by natural decline. By that time, 410 million tons of oil had been produced consisting of 144.5 million tons from Middle Miocene and 265.5 million tons from Mesozoic (mainly Upper Cretaceous) deposits.
As of Jan. 1, 1990, of 40 oil pools being under commercial development and production test, 17 pools were 91-98% depleted and 9 pools were 70-90% depleted.
The reserve structure worsened and the share of ineffective and stranded reserves increased. Oil production in Grozneft declined to 4.2 million tons followed by further decline: to 3.93 million tons in 1991, 2.92 million tons in 1992, 2.63 million tons in 1993, 1.15 million tons in 1994, 622,000 tons in 1995, and 320,000 tons in 1996.
As of Jan. 1, 1997, 421 million tons of oil, 45.5 billion cu m of associated gas, and 641 million cu m of nonassociated gas were produced.
Development status
A level of commercialization of the initial potential resources and commercial oil reserves in OGBP reached 80%.
By 1995, 8 Middle Miocene, 2 Paleocene-Eocene, 23 Upper Cretaceous, 9 Lower Cretaceous-Aptian, 1 Lower Cretaceous-Barremian, and 1 Lower Cretaceous-Valanginian + Upper Jurassic deposits had been under development.
Grozneft's oil and gas reserve stock included 24 fields (44 pools). Probable oil reserves reach 192.6 million tons of equivalent fuel including 16.6 million tons in Upper Cretaceous deposits, 8 million tons in Lower Cretaceous deposits, 58.9 million tons in Upper Jurassic deposits, and 109.1 million tons of gas.
Initial oil and gas reserves in place amount to 524.9 million tons and 192.6 million tons, respectively (717.5 tons equivalent fuel in total). However, it is quite possible that the potential hydrocarbon resources in the OGBP may be doubled.
Deeper potential
The reserves will increase considerably if we take into account the resources of the thick oil-and-gas bearing complex of Jurassic deposits, not only its upper units but also middle and lower ones, as well as pre-Jurassic formations.
It should be noted that discovered and developed pools will be characterized by considerable depth of occurrence, small size, poor reservoir properties of pay beds, complex geological and engineering conditions of drilling, and high H2S content.
Deep disjunctives run through the whole sedimentary cover of the OGBP, and their roots run into the subbasement part of the lithosphere. The deep disjunctives not only formed a present structural plan but also promoted the formation of oil and gas generation zones, migration paths (cross-flows), accumulation objects, and hydrocarbon fluid conservation.
Tectonic movements are traced as "vertical columns" and chains of oil and gas deposits. S.G. Neruchev (1969), studying Karabulak-Achalukskoe field, noted the absence of oil migration traces beyond the arches of the structures.
Besides this field the same characteristics can be attributed to Alkhasovo-Malgobek-Voznesenskoye, Eldarovskoye, Khayan-Kortovskoye, Mineralnoye, Bragunskoye, Oktyabrskoye, Pravoberezhnoye, Chervlenskoye, and Severo-Mineralnoye fields, as well as many gas and gas-oil fields of submontane Dagestan including Dimitrovskoye, Makhachkala, Ternair, Gasha, Achi-Su, and others.
Usually the pools of the above mentioned fields occur in combination traps with tectonic and lithological shielding in terrigenous reservoirs and in traps of massif type—in carbonate reservoirs confined to the zones of destruction and dilatancy. Fractured zones are not always confined to the crests of thrust structures; often they are confined to their wings and periclinals.
The analysis of geological structure and oil and gas accumulation of the region considered as a whole and its separate pools with the attraction of the principles of faulted tectonics has allowed refining of the mechanism of hydrocarbon accumulation formation and to diversify their types.
This work will simplify the solution of forecasting problems in similar oil and gas bearing and perspective regions, such as stratifirmal, veined stockwork, massif irregular form, nest-like, and chambered veins (often in cavernous voids of limestone).
Almost all known types of ore formations have been found during the investigation of commercial liquid hydrocarbon pools.
There are examples that the above traps of hydrocarbon fluids have been found not only in the Tersk-Sunzhen oil-and-gas bearing region of Eastern Ciscaucasia but also in the Salymsk and Krasnoleninsk regions of Western Siberia, the Yurubchen-Takhomsk zone of Eastern Siberia, the Dnieper-Donetsk trough, and many other oil-and-gas bearing regions throughout the world.
Deep exploration
Until the 1990s, the OGBP was the most productive area in the North Caucasus, and even now this region has high prospects for deep (below 5,000 m) oil and gas.
This is evidenced by commercial oil inflows obtained on the Alkhanchurtskaya well 1007 (5,800 m) of Pravoberezhnaya and other areas and hydrocarbon gas obtained on the Khankalskaya well 11 (5,812 m).
By 1986, more than 2,000 deep (over 4,500 m) wells had been drilled in the Former Soviet Union, and many of them had been drilled in the OGBP. The same depths are in practice in the oldest oil-and-gas producing region—Azerbaijan (Bulla Island, oil from the depth of 5,755 m; Bulla-More, gas from the depth of 6,200 m).
According to predictions made by Azerbaijani scientists (academician Sh.F. Mekhtiev, academician S.G. Salaev, and others) in the 1980s oil accumulations in this region are to be expected at depths of 9,000 m. These predictions are also based on the practice of oil and gas resource development in the US.
Extensive drilling activity has proved that at depths of 5,000-7,000 m there are terrigenous and carbonate reservoirs with satisfactory filtration and capacitance properties providing a gas well output of 3-6 million cu m/day, oil output of 50-300 t/d, and condensate output of up to 200 t/d.
The analysis of the available geological and geophysical data on deep Cretaceous and Jurassic deposits on the territory of the OGBP brings out clearly the presence of prospective objects for oil and gas exploration. This, thanks to discovery of new hydrocarbon accumulations and stimulation of oil and gas production on old areas, will enable a progressive growth of oil production to 2 million to 3 million tons/year.
Stabilizing production
A brief stabilization of oil production in Chechen Republic in the beginning of the 1990s at a level of 4 million tons/year was possible at the expense of new deep fields.
The maintenance of this stabilization after the recovery of oil fields and transportation system is related, first of all, to searching for pools in Cretaceous and Jurassic sections, including traps of nontraditional types confined to zones of rock softening (dilatancy and destruction), as well in Middle Miocene and Lower Miocene formations where hydrocarbon accumulations may be found in traps of lithological and tectonic boundary, local wedging out of sand reservoirs.
According to the above forms of location of ore bodies of native occurrence, it is possible to forecast new types of liquid hydrocarbon accumulations (oil and gas-condensate). In this case it is useful to compare and analyze the results and methods of searching for deep minerals accumulations in different structural and tectonic situations by nontraditional methods.
One should also consider in a complex of prediction criteria distinctive features of deep oil and gas bearing formations (especially filtration and capacitance properties of rock-reservoirs and rock-fluid traps; the last condition considerably separates "mobile" hydrocarbon accumulations from "fixed" forms of ore bodies), and evaluate the capability of drilling to technically accessible depths assuming that profitable flow rates and commercial reserves volumes can be expected.
A vast array of exploration methods is well known (different seismic surveys, gravity prospecting, magnetic exploration, electromagnetic and radio-wave survey, geochemical and aerospace photography, analysis of heat flows).
New stimulation methods including steam treatment (development work was conducted on Well 440b of the Starogroznenskaya area in the Chokraka formation 10 in 1976-77) and thermal treatment of bottomhole of pumping Kargano-Chokrak wells and other methods are needed for wide introduction in the OGBP.
The available geological and geophysical information allows one to substantiate and take effective technological measures on improving the oil recovery factor. To enhance oil and gas recovery, complex measures on developing and introducing fundamentally new stimulation methods are required.
Summary
The Chechen Republic is a territory of oil production, hydrocarbon processing, and one of the oldest regions in the search for oil and gas fields.
The republic has come to the 110-year anniversary of the Grozny oil industry. Oil production is gradually increasing. In 2002, Grozneftegaz produced over 1 million tons of oil. In the future the republic plans to develop the hydropower and recreational resources in its piedmont and mountain regions.
In the author's opinion, it is necessary to solve the following basic issues related to oil production and processing and development of infrastructure in the republic at large:
- Working out and adoption of a new law on allotment of land for the drilling of oil and gas wells.
- Provision of environmentally clean technology of well drilling and oil and gas fields development.
- Application of corrosion-resistant equipment for drilling in the formations with products contaminated with H2S and carbon dioxide; drilling rigs with electronic equipment for prediction and automatic control of geological and technological conditions of well drilling; high-quality tubing and bits; blowout preventers, etc.
- Restoration of wells, oil and gas processing plants, systems for storage and transportation of hydrocarbon raw stock, processed products, and other infrastructure.
- Establishment and development of scientific and industrial relations between researchers and management staff of various gas and oil bearing regions, specialized institutes, academies, foreign firms engaged in the development and implementation at the republic's fields of oil production intensification, enhancement of oil recovery at the final stage of fields development, scientific prediction, and substantiation of prospecting new deposits deep-seated (below 5,000 m) in promising zones, still concealing large hydrocarbon reserves.
The author
Igor V. Istratov has worked in the Vniigaz Ltd. Gazprom JSC since 1995. He participates in substantiating raw material bases of gas and condensate production for the Gazprom JSC and all of Russia and analyzes the raw material bases, hydrocarbon production, and export supply potential of various countries. He is a graduate of Grozny Oil Institute and has a doctoral degree in geology and minerals from Baku Geology Institute of the Azerbaijan SSR Academy of Sciences.
