Geology
Conformity of Oil and Gas Content Advancement within the Western Part of the Turan Platform
Azhgaliev D.K. LLP «Nedra-Engineering Company», Almaty RKIn accordance with the characteristics of the regional tectonic position, the western part of the Turan platform is presented by the North Ustyurt (the same name system of bending and upheaval), Bozashinskiy upheaval and the surrounding areas of Mangyshlak and Prikarabogazya [3]. According to the results of the regional project "integrated study” of sedimentary basins of the Republic of Kazakhstan" (Akchulakov U.A., Karabalin U.S., Iskaziyev K.O. etc .; 2009-2013), made on the initiative of JSC NC "KazMunayGas" and geology and subsoil use Committee of the Ministry for investments and development of Kazakhstan, the northern part of the territory that respectively combines in the east and west the North Ustyurt and Bozashinskiy upheaval, separated into the Ustyurt-Bozashinskiy pool [5]. Adjacent to the south, districts Mangyshlak and Prikarabogazya are assigned separately to Mangyshlak sedimentary basin in the composition of, consistently oriented from north to south, Central Mangyshlak-Ustyurt system of dislocations and South Mangyshlak system of bending and upheaval [3, 4].
Historically, the territory in question was developed and was part of a single East European-Turan lithospheric platform (Zholtayev G.Zh .; 1998). Influence of the Ural-Tien Shan pale ocean in the east and Paleotethys - in the south, resulted in the formation of intercontinental rifts (the South Emba, Bozashinskiy, Mangyshlak). As a result, in the south of the lithospheric platform large blocks have been formed (Kara-Bogaz-Gol, North Ustyurt, Srednekaspiyskaya microplatform, Mangyshlak, and others.) [6]. From the perspective of the common history of the entire western part of the Turan plate (the North Ustyurt, Bozashi, north Mangyshlak and Prikarabogazya) and similar in composition forming the foundation and Paleozoic strata structural-formation complexes, this article with that in mind considers patterns in the spatial distribution of oil and gas content, placing the main oil and gas bearing zones and oil and gas containing strata.
Currently, the study area, based on the territory of Kazakhstan and Uzbekistan, identified 86 fields, including 55 in Mangyshlak and 31 in the North Ustyurt and Bozashi. The deposits of oil and gas condensate are found in the sediments of the Paleozoic, Mesozoic and Cenozoic. Moreover, in the Mesozoic and Cenozoic deposits are found in almost all stratigraphic levels, from the Jurassic to the Paleogene. Taking into account the available data and the reached stage of study of the spatial distribution of oil and gas potential in general, the below listed characteristics are indicated.
In the north of the territory within the Ustyurt-Bozashinskiy basin certain zoning in the phase composition of hydrocarbons is marked. In the eastern part the composition of gas and gas condensate deposits tend to dominate (Arystanovskaya, Karakuduk, Shagyrly-Shomyshty, Bozoi, Kyzyl, Akkulka, Kokchalak, Urga, etc.). While in the west mainly oil deposits are distributed (Bozashi North, Arman, Kirel, Karajanbas, Karaturunskaya group and others.). Oil deposits in the west by hypsometry located above regarding gas and gas condensate deposits in the east of the territory. In this regard, revealing the gradual immersion of the surface of the Paleozoic from west to east in the depth range of 2,0-4,3 km and, as can be seen, the different nature of occurrence of the Paleozoic strata in the west and the east of the territory. Perhaps, the eastern part of the territory is characterized by a more active formation of oils of early generation.
Noteworthy is the recent discovery of oil reserves in the Jurassic-Cretaceous deposits in the area Akkulkovskaya in the north-eastern part of the Ustyurt-Bozashinskiy Basin, which traditionally has been characterized mainly by gas deposits and, as known previously, the search for oil deposits have been unsuccessful in this part of the basin. The correlation of favorable conditions and the area of data Akkulkovskaya on the surrounding areas, of course, will enhance further the effectiveness of the search for new oil fields in the east and north-east part of Ustyurt-Bozashinskiy basin.
Location of deposits in the plan points to their confinement to areas of major tectonic elements of II- order (Figure).
The degree of saturation and density of HC deposits on the territory as a whole is uneven. So, on Mangyshlak main zones of oil and gas content (hereinafter - ZOGC) are confined to Zhetybai-Uzenstage and Peschanomyssko-Rakushechnaya zone elevations, on which there are 28 and 7 fields, respectively. Of the identified 55 fields of Mangyshlak only 3 (Uzen, Zhetybai and Tenge) have about 90% of the total identified reserves of oil and gas condensate. On Bozashinskiy upheaval there are 10 fields, and it is characteristic that they have a different order, and also in relatively close proximity differ from each other by the amount of reserves. Within North Ustyurt fields 8 are focused on the main part (Akkulka-Bazaysky shaft Arystanovskaya stage Koltyksky deflection). 13 deposits are confined to the south-eastern part (Aktumsukskoe uplift Kuanysh-Koskalinsky / Alambeksky, Tahtakairsky shafts,Barsakelmessky and Sudoche deflections).
It is evident that certain accumulations of oil and gas condensate are confined to local upheavals and structural areas of "delays" on the sides and the slopes arches and troughs. In larger terms, these laws allow differentiating the territory of a system of large positive and negative elements that with the structural position may well be considered as areas of hydrocarbon accumulation and oil and gas condensate clusters.
In general, particularity of oil and gas potential of the territory (Ustyurt-Bozashi, Mangyshlak) is largely predetermined by the influence of trends and fault tectonics. In turn, the structural plans of almost all of identified major elements of II- order on the surface of the foundation and the roof of Paleozoic strata are in good agreement with each other.
Currently, oil and gas potential of the territory is characterized by a considerable degree of depletion of the main Uzen-Zhetybai, Bozashinskiy and Karagiynskiy groups and deposits associated with Jurassic and Cretaceous sediments. Accordingly, this makes it necessary to implement the most urgent task for the Mangistau region to fill the raw material base for hydrocarbon exploration by setting in promising areas and expanding the productive area known ZOGC, including engaging in exploratory research more immersed intervals section from Paleozoic strata. Practical interest from this point of view also, seems objective in the historical aspect with the light of the new data and achievement in the stage of study.
Due to the receiving of the production inflows of UV in the Paleozoic Peschanomyssko-Rakushechnoy complex of a zone of upheavals (Oymasha), the Kuanysh-Koskalinsky shaft (Karachalak, Kokchalak), the Sudochy deflection (Urga Northern) and oil and gas content on separate structures of Prikarabogazya and the South of Mangyshlak (Alamuryn Youzhny, Tamdy, etc.), further more detailed studying of features of interior and prospects of oil-and-gas content of this complex becomes particularly important [1, 7]. The absence reasons so far of fields of UV, new and significant, in deposits of the Paleozoic in other territory, we believe, in many respects is poor degree of study of this complex drilling. The available geologic-geophysical materials, despite their restricted volume, nevertheless allow at the reached study stage from more optimistic positions to consider prospects of a Paleozoic complex in the oil-and-gas relation taking into account following favorable prerequisites.
- The production inflows of UV on the areas of Oymash dated for decompactification zones in an area of development of the granite intrusion are received. The considerable expansion to the South (up to the Gulf Kara-Bogaz-Gol) territories is predicted with simulated condition of bedding. At the same time, not only breeds of a sedimentary complex are of search interest. In the conditions of the site Peschanomyssko-Rakushechnogo of Mangyshlak deposits of UV contact also the zones of subdivision and a decompactification put by granites and granitoids. According to Maylibayev M. M. (2014) high values FES in the arkozakh – the educations created in situ subdivisions and a decompactification of the intrusion are noted. Porosity and permeabilityin breeds makes 15-23% and to 1,8 mkm2, respectively [7].
- As noted above, deposits of the Paleozoic are oil and gas bearing on a number of the areas of a southeast part of the Ustyurt-Bozashinsky pool in the south of Northern Ustyurt (Kuanysh-Koskalinsky and Takhtakairsky shaft, Barsakelmessky and Sudochy deflections). Except the squares mentioned above on which the production inflows of gas and gas condensate are earlier received still in some cases intensive gas-manifestations (Chibina, Kushkair Tsentralny, Murun), non-commercial inflow of naphtha (Karakuduk), direct signs of UV and confirmation of probable efficiency according to GIS are received (Karaumbet Severny, Akchalak, etc.). Estimated deposits in the Paleozoic contact carbonaceous deposits of upper devonian (famenian), lower-mid-carboniferous and coal lower permianage [1].
The data indicating processes of vertical migration of UV of Paleozoic thickness and secondary genesis of some large deposits in a Jurassic and cretaceous complex are obtained. So, according to the qualitative characteristic of naphtha and the analysis of a structure of Bozashinskiy ZOGC excess of the confirmed volumes of reserves of naphtha and gas of the production categories over generative opportunities and potential of the Jurassic producing thickness is established (Akchulakov U. A., etc.; 2009-2013). It suggested existence of padding subcurrent and the subsequent migration of UV in Mesozoic deposits from more deep intervals of a section, the bound to the Paleozoic to a large extent. Besides, the fact that for Jurassic deposits of Zhetybay-Uzensky ZOGC the main source of UV was the Paleozoic complex specify these definitions in naphtha of the Mesozoic of maintenance of microfossil of migratory character (microfossils of a vegetable and biogenic origin) corresponding to the Paleozoic. Presence at the Jurassic and Triassic naphtha of Mangyshlak the upper Paleozoic (carbon fabrics) of upper Paleozoic assumes high probability of the dominating role of vertical migration in clustering of UV in the Triassic and Yura. Taking into account these factors, and also the regional structural and tectonic plan and features of development of fault tectonics it is difficult to assume the considerable lateral redistribution of UV in a section of this region.
The nonuniform, "speckled" arrangement of deposits in the plan and, at the same time, many-tier their placement in a section of upheavals at the level of the meso-Cenozoic, pointing to possible communication of deposits and ZOGC with the expressed trends and areas of an extension the fault of zones is characteristic. Taking into account it for the larger territory of the West of the Turan plate the character differentiated on the area and localcoal mine formation of congestions UV with a confinedness to elements of the 2nd order testifying to high prospects of large raisings in a Paleozoic complex is supposed.
In addition, the group structure of bitumoid and coefficients of bituminization of organic matter making in a clay-aleurolitic breeds of 0,8-8% and up to 26-78% in the carbonates containing secondary bitumens point to processes of deep migration of UV. In a complex with direct shows of naphtha (Karakuduk) and gas (Karachalak), it allows assuming possibilities of oscillation of UV Lower Carboniferous and upper carboniferous-lower permian deposits (by analogy with zones in east part of the Ustyurt-Bozashinsky pool). By these calculations, existence of deep vertical migration is supposed on the breaks and conductive channels created, in turn, at the expense of deconsolidated zones.
According to reinterpretation of seismic materials 2D and 3D (2013-2014) in a section of the Zhetybay-Uzensky step on the Paleozoic the packages of reflections which are unambiguously indicating stratified thicknesses are allocated. The further analysis allowed in Ustyurt-Bozashi coal mine and Mangyshlak is proved to allocate a roof of the Paleozoic (OG as clear and sure seismic boundary. Along with it possibilities of selection in the thickness of the Paleozoic at this step of large search objects (a zone of Uzen – Karamandybas – TengeTenge Western) at depths of 4,5-5,0 km are confirmed (Zholtayev G. Zh., Isenov S. M., Kovrizhnykh P. N., etc.; 2013). High prospects in this case are proved by the favorable seismic characteristic of an object and geochemical prerequisites in its assessment and the analysis. The main factor in justification were the seismic interpretation which is carried out on the alternate basis and, certainly, significantly the extended technical capabilities in processing and the analysis of data. It is supposed that a Paleozoic object is characterized by the tank of large type, reefogenic genesis is not excluded. Though this object is allocated tentatively, at the same time it opens ample opportunities of the GRR perspective trend recent for all Mangystau region.
At this stage of study taking into account results of complex studying of settling ponds for 2009-2013g.g., on Mangyshlak in Peschanomyssko-Rakushechnoy three objects on the Paleozoic on which prospects are proved by analogy with conditions of the region of the area of Oymasha are allocated to a zone for statement of GRR.
In relatively more studied Mesozoic part of a section the provision of the known deposits of UV closer to the North naturally coordinates with the regional tectonic elements and traps located as a part of the corresponding trends and structural lines extended in the width of northwest orientation. This compliance of local objects is very characteristic of the Uzen-Zhetybaysky step, the Karatau and Beck-Bashkuduksky shaft, and also the sublatitudinal peripheral strip defining a northern board of the Mangyshlakskiy basin. Within the more indicative in this regard Burmasha-Bodrayskaya, Uzen-Zhetybaysky step sequentially from North to South are markedMaldybaysky, Turkmenoy-Alasaysky, Uzen-Karamandybassky, Zhetybaysky and Tenge-Tasbulatsky zones of trends and structural lines which unite all perspective local upheavals – potential objects for statement of search drilling [2]. In the separate structural line local upheavals on some indexes (the area, the sizes, amplitude of a trap, features of phase structure of deposits) submit to a particular order. Search works are reasonably accented on separate upheavals / links of the structural lines located in zones between the known fields. If to present local objects in a transverse section (to an extension cross), UV deposits with small stocks are often localized in traps, representing structural "delays" on extensive monocline (Enorta, Karamandybas the southern slope, the Tenge zone, etc.). It is not excluded that for UV anticlinal upheavals and objects, also large and average on the area, dated for flexural complications, breaks and zones of lithologic replacement can be traps.
The tectonic scheme of a Paleozoic complex of the West of the Turan plate (according to Akchulakov U. A., etc.; 2012)Legends:
1. Contours of structures of the I order / pools: A – Prikaspiy, B – Ustyurt-Bozashi, C – Mangyshlak;
2. Contours of regional structures of the II order: 1 – The Bozashinsky raising, 2 – the Southern Bozashinsky deflection, 3 – the Arystanovsky step; deflections: 4 – Koltyk-Kulazhatsky, 5 – Kosbulaksky, 6 – Shalkarsky, 7 – Barsakelmessky; 8 – Sudochy, 9 – the Beck-Bashkuduksky shaft, 10 – the Zhetybay-Uzensky step, 11 – the Shelly raising, deflections: 12 – Zhazgurlinsky, 13 – Karabogazsky, 14 – Assake-Audansky, 15 – Ciscaucasian and Caspian, 16 – the Tuarkyrsky raising, 17 – the Peschanomyssky deflection, 18 – the Alambeksky shaft;
3. Regional breaks: I – North Ustyurt, II – Central Ustyurt, III – Takubaysky, IV – Aralo-Kyzylkumsky, V – North Karatau;
4. Isohypses on a roof of a Paleozoic complex, km: OG V – Ustyurt-Bozashi/OG “b” – Mangyshlak and the Central Caspian Sea;
5. Local raisings and troughs;
6. State borders of Kazakhstan.
One more important feature is that structural lines directed from the southwest on the northeast are differentiated among themselves according to certain phase structure of UV, determining important regularity of vulgar distribution of deposits with structure of UV [2]. Depending on hypsometric situation and belonging of deposits to the particular structural line, UV deposit in the direction from the South to the north are characterized by gradation from a condition of lungs on structure and saturated with gas (Tenge) to deposits with high viscosity and petrobituminous rocks (Zhangurshy, Tobedzhik).
The available data specify that formation of deposits of UV in this part of the territory is bound to fault tectonics to a large extent, and the tectonic criterion of oil-and-gas content among others is considered as a major factor here. Therefore, the oil-and-gas potential of Mesozoic deposits of Mangyshlak is, still, highly appreciated [5]. West Zhetybayskoye upheaval, two objects in a strip of the structural line of KaragiyeSevernoye - ZhetybayYouzhny – Tenge, and also local objects dated for a Paleozoic ledge in the zone Kurganbay-Kokumbay are prepared for statement of search drilling.
In the southern and central part of Mangyshlakdeposit of UV are expected on local objects of the "subjacent" inherited development, for which, apparently, rather higher degree of safety of probable deposits of UV will be characteristic. Great opportunities for detection of new deposits, in particular in Paleozoic deposits, are decided by a genetic linkage of potential ZOGC on breaks and zones of a jointing and deconsolidation created along them. In these zones distribution of the reference breeds collectors of fracture type, and in case of statement of basic researches, it, undoubtedly is expected, will be the main factor of increase in effectiveness of basic researches. In rather northern areas of the territory (Tyub-Karagan-Karatauskaya a folded zone, the Zhetybay-Uzensky step) that differed with more fissile tectonic mode against the background of regional rise in sedimentary thicknesses and development of sublatitudinally extended stretched building blocks and steps, local objects mainly of Prirazlomnoye, tectonic and lithologic screened character are assumed.
For Northern Ustyurt and Bozashy natural communication of space placement of deposits of UV with zones of a joint of positive and negative structures of the II- order is supposed. New deposits are dated for the zones of stretched breaks allocated on the surface of the base. Results of the analysis of geochemical data and features of the near fault of sites to which development of a jointing and zones of a decompactificationare accompanied, show a favorable character of this relation. Presumably, slopes of the Koltyksko-Kulazhatsky zone of deflections, onboard zones of Samsky and Kosbulaksky deflections meet the case. As an example and analogy – a confinedness of Akkulkovsko-Bazaysky group of deposits to the southern board of the Shalkarsky deflection (drawing).
In common assessment of oil-and-gas complexes of Northern Ustyurt the considerable potential on UV contacts Paleozoic thickness which at present taking into account possible interpretation of sheeted inhomogenedthities and internal "stuffing" in general, is represented on seismic materials more legiblly. The upper Devonian- lower Permian range of a section presented mainly by deposits of carbonaceous structure, earlier opened and known on cuts of basic wells on structures of Kush-Ata and Eligazhi is perspective.
The analysis and synthesis of data on regularities and geological features of a spatial distribution of oil-and-gas content and assessment of hydrocarbonic potential of the western part of the Turan plate together with the adjacent territory of Mangyshlak and Prikarabogazya allow proving the following important conclusions.
1) Earlier assumed stable relation of conditions of sedimentation in the Paleozoic and the Mesozoic with block structure of the base which, as we know, influences duration of stages of a sedimentation is confirmed. Distinctions in depths of separate blocks predetermined variability of lithologic structure and thickness of deposits and, respectively, distribution of possible oil-and-gas complexes. It is necessary to pay special attention to studying of regional deep breaks and an intense and straining condition of Paleozoic and Mesozoic thickness since structural and tectonic conditions are defined by a situation of geodynamic stresses.
2) On Northern Ustyurt Barsakelmessky and Sudochy (the southern and southeast part) the main generative zones are considered to be Kultuksky, Samsky, Kosbulaksky (the central and northeast part). Taking this into account, detailed basic researches should be accented on onboard both the near edge zone parts of these deflections and zones of near edge zone monoclonal. It is predicted perspective local raisings of structural and unstructured type. Now high prospects for results of the complex analysis of pools (2009-2013) characterize a number of the prepared structures (Kyryn Vostochny, Boldar, Samskaya, SheluranYouzhny, Kumsuat, Island, Tepke) which is of search interest.
3) In the considered territory, despite weak study, seismic exploration and drilling, further studying and searches of deposits of UV, the bound to large objects / Paleozoic raisings represent high-perspective. Considering lack of systematic and targeted studying during the previous periods, it is possible to assume that earlier drilled wells on the upheavals revealed on the Paleozoic opened traps are more often not in optimum conditions. Earlier lack of systematic researches and accurately verified strategy of search works could not provide nevertheless standard preparation of traps in Paleozoic thickness.
4) Clustering of UV on Mangyshlak happened due to realization of generative potential that varies on an age and facial structure of oil source complexes. Taking into account data of studying of biomarkers the structure of relict connections is various and testifies to the favorable prerequisites for selection in a Paleozoic complex of self-contained oil-and-gas complexes.
5) On the example of the Zhetybay-Uzensky step and certain regions of Southern Mangyshlaksky system of bending and upheavals structural plans of Paleozoic thickness are characterized by compliance and autonomy to the above-lying various lithologic-and-stratigraphic complexes of a pre-Jurassic complex. Respectively, for these zones the inherited development and lack of the considerable restructuring at a turn of the Paleozoic and a Permian-Triassic is supposed. In this regard and considering features of development of fault tectonics, there are favorable prerequisites that Paleozoic deposits will also contain UV deposits in a section of large objects of structural type on which efficiency of Mesozoic deposits is earlier revealed.
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