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Geology

Ustyurt – real testing area to discover cluster of oil, gas and condensate fiel

“It is required to start the work on new fields’ exploration” – N.A. Nazarbayev, at extended RoK government session on August 06, 2014.

The article presents an industrial innovative project in which implementation of the new trend in exploration (including seismic investigations) and drilling works at Tasoyuk subsoil area is offered for the purpose of enhancing the possibility to discover natural gas and treat it with due quality. That means putting intellect, knowledge and understanding into hydrocarbon accumulations’ search, exploration and development.

The justification for innovations in exploration drilling works at Tasoyuk subsoil area is presented as being an innovative industrial trend in accordance with which special drilling mud will be used during geological (including seismic) and drilling works, as well as the reduction to the minimum of the overbalance pressure and exposure time will be ensured; moreover, dipole shear sonic imager, modular dynamic drill-stem tester, Platform Express technology will be used.

KEY WORDS: Implementation of innovative trends in drilling exploration works, new trends in seismic investigations and in drilling works, increase of  probability of the discovery of gas deposit presence, usage of vortex cooler during gas processing, dipole shear sonic imager, modular dynamic drill-stem tester, Platform Express technology.

New fields discovery is possible within Ustyurt both in Shakhpakhty stage and within frontier Assakeaudan deflection. Based on information from M.M. Mailibayev, Candidate of Geological and Mineralogical Sciences, who has been working in oil and gas production industry of Kazakhstan since 1957, published in the Collection of Articles of Geological Sciences Institute named after K.I. Satpayev “Geological Science of Independent Kazakhstan: achievements and prospects” dedicated to the 20^th Anniversary of Independence of the Republic of Kazakhstan, December, 2011 – High-prospective Ustyurt territory for oil and gas bearing capacity is represented by a triangle. Ustyurt triangle belongs to Aktobe and Mangistau oblasts administratively and to Karakalpak oblast of the Republic of Uzbekistan partially (Figure 1) [1].

Regional tectonics and oil and gas bearing capacity of the large block between South Emba Paleozoic elevation, Central Mangyshlak anticlinorium and meridian Hercynides of Ural-Aral lineament divide Turanian Platform into two independent blocks in geological evolution of the block: Ustyurt and Torgai-Kyzylkum. Angles of Ustyurt triangle are closed by Yuozashy elevation in the west, Pre-Mugodzhar (Shalkar) depression in the north, and Barsa-Kelmes or Sarykamysh deflection in the southeast.

1 – the southernmost tip of Ural (Kazakh Ural); I a – Or-Ilek elevation, I б – Mugodzhars;

2 – periphery of bottom tip of Ural; II a – Aktyubinsk Aral Sea region, II д – southwest part of Turgai plain;

3 – South Mugodzhar region, III a – Caspian Depression, III б – South Emba, III в – Pre Ural Plateau;

4 – Mangyshlak; IV a – Mangyshlak Mountains, IV б – Buzachi peninsula, IV в – South-Mangyshlak Plateau;

5 – Ustyurt; V a – Ustyurt Plateau, V б – Pre Ustyurt Plain; 6 – border between regions;

7 – border between subregions

Figure 1 - Ustyurt layout in West Kazakhstan territory zoning

Correlation to the structure of Ustyurt outlines will allow detailing deep structure of the entire block, where sedimentary sequences development are reflected at the transition from one large oil and gas basin to another along medians of the triangle. This methodology will allow commencement of successful geological exploration within the entire territory of Ustyurt and certain outlining of deep geological features for the exploration of commercial hydrocarbon deposits in concealed traps on consolidated multiple-aged basement. In this area, the rates of geological exploration is decades behind the production rates in RoK bordering regions. Currently, after 23 years of the Republic independence, it is high time to foster the central territories of Ustyurt which are difficult to access, and even Pre-Caspian territories at the highest success ratio not exceeding one third. Obviously, over the years, the depths of prospective formations increase; and at the same time, the potential of both the Mesozoic and Paleozoic deposits embedded on Caledonian and Baikal basements  of the South-West Kazakhstan (West-Kazakhstan, Atyrau, Aktobe, Mangistau and Kyzylorda oblasts) increases.

Inversion constitution on intermediate tectonic structures allows identifying very distinctive directions of prospecting works for oil: between the Bozashy and Pre-Caspian; the Mangyshlak and Sultanuizdag; the Aral and Mugodzhars. First researches with new representation of geological structure beginning from northeast angle are works of A.L. Yanshin in 1930s of the last century. Hidden dislocations of meridian orientation are marked where there may be traps of hydrocarbons [9]. Bazaysk group of deposits and Akkulka are the first confirmations.

A.L. Yanshin closes the Eastern flank of Ustyurt with Mugodzhars Hercynides buried under Aral to Sultanuizdag. He also spreads zone of concealed Hercynides from Bozashi through South Ustyurt, which connects with the Mugodzhars Hercynides in the south [6].

In 1960sgeological studieswere directed from the Mugodzhars along the south-east flank of the Pre-Caspian Depression, i.e. along border of North Ustyurt where there is upper Paleozoic (Devonian, Carbonic and Permian) of platform type. Saliferous Kungurian is facially replaced with intraclast one with a trend of thickness increase together with Devonian and Carbonic within Turanian Platform. «Deep immersion of Upper Paleozoic folded basement» sharply differentiates Mesozoic platform cover with elevation of even sublatitudinal course [2, 4]. Gas content of the north flank on Shagyrly and Shomyshty buried structures and oil content on Karakudyk, Koltyk and Borankol are confirmed.

South, posterior – late-Caledonian basement with conspicuous inversion in Mesozoic is prospective for hydrocarbons in open deposits uncovered in Karakalpak (Shakhpakhty) and in southeast angle (chain of fields from Kansu to Vozrozhdeniya island). In the central part of the triangle, Arystan field was discovered.

Neogene shield of shell deposit fully hide tectonically calm Ustyurt triangle creating both geographic and hydrogeological difficulties. Based on unique environment, where there are many raw hydrocarbon deposits, we have grounds for certain feasibility of geological exploration. Three large areas have been already approximately defined. They are not large on elevation amplitude on Bozashi, Karabauyr and Aktumsyk, between which there are such deflections as South Ustyurt or Sarykamys, North Ustyurt and South Bozashi or North Aktau. At the border with Emba elevation as per course of Pre Caspian border a large tectonic lineament is sublatitudinally marked. It is monocline with clearly defined inversion on Upper Paleozoic with the thickness exceeding 3500 m in comparison with Mesozoic with the thickness from 600 m to 1400 m [8]. In central part (Aktumsyk), except for deposits in Lower Cretaceous and Jurassic, we expect vast accumulation of hydrocarbons in flat-lying brachy-anticline of Permian-Triassic, Carbonic and Upper Devonian at the depths up to 6300 m.

The South of the triangle is a zone or part of intensive deflection in Mesozoic on almost “bare” Caledonian basement, which is clearly observed within Mangyshlak plateau and Karakum fold. South Ustyurt and South Mangyshlak are divided by depth crushing zone with embedding of granitic intrusions over fractures, which within a period of late caledonides supplied fragmental materials of sand-and-gravel composition (arkoses) to the north to Bozashy, Sarykamys and Barsakelmes deflections. This coarse-grained material from South Mangyshlak formed series of Upper Paleozoic creating large elevations Bozashy and Baishagyr after inversion. Immersion of Mangyshlak dislocations south-eastward under the appropriate angle of Ustyurt triangle allows forecasting deep cracking of oil fractions forming gas deposits both in Upper Paleozoic and in Mesozoic-Cenozoic. This zone, according to S.E. Chakabayev and others, has no prospects [8]. The evidence of Paleogene prospect in South and East Ustyurt was the discovery of Shakhpakhty, Bazoi, Zhaksy and Zhaman Koyankulak fields in 1961 [2]. 

The formation of recent gas deposits occurred as a result of insignificant elevation of this angle at the border of Oligocene; however, the entire Ustyurt territory was not subject to relative fluctuations of the basement, which positively affected the preservation of reservoir formations starting from Upper Paleozoic. It is very difficult to identify thickness change of sedimentary cover between deflections and elevations, i.e. from North-Ustyurt deflection to Emba or Akkulka elevations, from Sarykamys deflection to Aktumsyk and Karakum elevations, which confirms the consolidation of the basement for a long period and syndepositional sedimentation. The role of short-term non-depositional hiatus is absent here except for border depth crushing zones – Emba, Mangyshlak and Aral [9]. Depth crushing zones at the early stages of platform development from Upper Paleozoic to Cenozoic imposed inversions movements from Karabogas fold through Mangyshlak anticlinorium and Bozashi elevation to South-Emba bordering uplift as borders of Turanian Platform. However, within Ustyurt triangle there is no big gradient of the entire Paleogene thickness. Mesozoic along Upper Paleozoic depends inversely, and it is closely connected with inversion within Perm-Triassic period. This process significantly affects huge prospects of oil and gas accumulations in Upper Devonian and Carbonic from periphery to the center of the triangle [7].

The most certain structure of Ustyurt is shown in structural-tectonic diagram prepared by P.I. Krayev and R.A. Shakhov in 1964, where east border crossing Aral in the east-western direction by Barsakelmes and Vozrozhdeniya islands with exit in the south to Sultanuizdag is not shown [4].

Sedimentary Paleozoic from north to south gradually reduces thickness from 7000 m to 2000 m, and Mesozoic increases it from 1300 m to 3500 m, determining inverse relation of hydrocarbons prospects and extending development of high-porosity reservoir formations on closed structures and clinoforms of long mileage as per the course of Ustyurt borders. Contradictions of deposit forms occur in the central part on Aktumsyk and Baichagyr elevations, where there may be brachyaxial folds with unpredictable course and unique sizes, which is confirmed by interrupted seismic profiles of unreasonable direction. Such structure is already observed on transition to the immersion of Mangyshlak anticlinorium under Ustyurt Plateau – Ushkuduk depression and Tuarkyr dike [4].

Conditional basement (PZ₁ – Lower Paleozoic) evenly immerges northward and westward to 7000 m. Judging by the depths, Permian-Triassic of Turanian Platform is required to refer to “basal” layers of platform cover repeated after Devonian (D₃) along the triangle periphery. Therefore, the most recent structure of Mangyshlak Mountain (E. Karatau) includes the late Carbonic of platform type in the cross-section; and Upper Paleozoic deposit deflections from north and south after the consolidation of caledonides are plentifully injected with granitoid intrusions [5]. Basement transition in Herсynides occurs after Karabogas elevation already. As a result of seismic interpretation, the basement might be Caledonian and underlay at the depths of 8-10 km. This is more recent than the Pre-Caspian basement, and the thickness of sedimentary sequence as well as oil and gas content prospects are not less than in surrounding regions.

Therefore, almost the entire Paleozoic, especially the Upper one, falls in maximum thicknesses of sedimentary formations between the Pre-Caspian flank and the South Mangyshlak, i.e. Middle and Lower Paleozoic falls in intermediate zone and Upper Paleozoic repeats bottom cycles along the platform periphery with the extension of accumulation areas due to consolidation of surrounding platforms of the Karabogas, Pre-Caspian and Turanian (eastward of Aral).

Hence, basic criteria of oil and gas exploration within Ustyurt at the depths from 2500 m to 5500 m and in the maximum from 6500 m to 7000 m are justified.

1. Lower and Middle Paleozoic within sublatitudinal zone closing frames of Bozashi paleo-fold with the exit in the west of Ustyurt.
2. Middle Paleozoic in the form of clinoforms justifies prospects within adjacent elevation zones of South Emba along large paleodike regardless the presence of positive structures against monocline including the Caspian shelf.
3. North-east angle and east framing of the triangle as deflection has deep depths of Upper Paleozoic with traps confined to shallow domes of Bazoi and Shakhpakhty type.
4. Throughly studied Mesozoic deposits along the triangle periphery allow forecasting traps only with multiple shallow deposits on structures concealed under Miocene with hydrodynamically closed form.

Based on Mesozoic structure it is possible to determine anticlines and domes in Paleozoic as folding inheritance on low-amplitude faults is observed everywhere as per data of deep seismic sounding, which, unfortunately, was not taken into account. Inheritance is also confirmed by syndepositional formation type of traps with the following preservation of elastic drive creating abnormal formation pressures and plunging contacts. All this requires expedited search of hydrocarbon fields confined to mioflank parts of the platform and zones away from deep faults.

Commonly known proven recoverable reserves of Kazakhstan without including the Caspian Sea shelf are about 2.8 billion tons of oil and gas-condensate. Approved reserves are estimated at 2.2 billion tons of oil. There is variance from 8 to 22 billion tons in respect of possible reserves but most experts agree that it is 12 billion tons of oil. Possible, recoverable resources of oil without including shelf fields are estimated to make up 6.3 billion tons. 70% of them are concentrated in the Western Kazakhstan and occur at the depth of 5000 meters and a little deeper.

More than 200 fields are discovered in the territory of Kazakhstan, containing commercial reserves. There are 98 oil, 67 oil and gas, 22 gas and 11 condensate fields. About 75 fields are under development.

Geographically, oil reserves are distributed extremely irregularly. 98.2% of fields under development are located in the territory of the western oblasts of the republic – in Mangistau, Atyrau, West-Kazakhstan and Aktobe oblasts.

In order to survive and develop the mankind at all times was looking forward to possessing energy. Last two centuries were marked by exponential increase of energy consumption per person being almost stable during previous centuries; the significant growth of technological diversity and the level of excellence of power plants of various purposes. Per-person consumption of finite fuel and energy resources will constantly increase almost in all regions of the world. As a result, overall consumption of finite energy in the world in the nearest thirty years will increase almost 1.5 times [10].

In the long-term prospective, by 2030, as per the evaluation of the International Energy Agency natural gas consumption in the world will be more than 4 trillion m³ [10].

In spite of strengthening competition in energy production due to the development of renewable energy sources and nuclear power engineering as well as the appearance of new ones in coal industry, natural gas remains one of the main types of energy resources.

Year by year, the role of oil and gas as export product increases, hydrocarbon production grows, but reserves are not replenished in required amount. Resources discovered and developed to the level of industrial use are left from fathers and grandfathers to children and grandchildren. Currently, hydrocarbon reserves are actively used without their replenishment.

Meanwhile, international industry cannot refuse from hydrocarbons acting as fuel [11].

Based on the International Energy Agency data “World Energy Survey”, 2009 (base case):

  World gas consumption, billion m³:

Worldwide consumption of natural gas will grow in average by 2% per year.

Kazakhstan presence at the world energy market will allow not only earning stable income from the export of gas, oil and oil products but significant strengthening political positions of the country in the world [11]. Therefore, it is required to facilitate the increase of efficiency of geological exploration and reserves’ replenishment and natural gas production increase accordingly.

In order to implement the newest progressive directions and technologies in drilling operations and geological exploration, KANTAR Oil LLP identified, justified and announced prospective coordinate subsoil area having named it Tasoyuk (Figure 2), where natural gas field will be discovered with high probability by means of the implementation of progressive directions in geological exploration (including seismic surveys) and drilling operations. Tasoyuk subsoil area is located in the south-eastern part of Mangistau oblast.

The discovery of new hydrocarbon deposits according to the conclusions of academician R.H. Muslimov: “We gain extensive knowledge, and this knowledge is above a field itself, above hydrocarbons».

Figure 2. Overview map of Mangistau oblast, where Tasoyuk subsoil site is located in the southeast part

We consider Shakhpakhty stage and partially Assakeaudan deflection (Figure 3) as the main prospective coordinate territory marked by KANTAR Oil LLP (Figure 2). Large gas field is operated in Shakhpakhty stage since 1971.

Author's interest in Tasoyuk subsoil area was formed long ago (in the periods of 1976, 2003 and 2011) till the discovery (in May, 2009) of the second large Dzhel gas field on the cross-border territory located 10-15 km to the south-west of Shakhpakhty field within 5-10 km from Kazakhstan border. Expected reserves are from 45 to 60 billion m³ of gas and more. Reserves on Tasoyuk subsoil area proposed by KANTAR Oil LLP are expected to be from 50 billion m³ of gas and more.

Shakhpakhty gas field is located in the territory of Uzbekistan and at the distance of 18-25 km from the border of Kazakhstan. It could be categorized as developed field, where gas is produced in excess of its reserves – 50 billion m³ confirmed by CCD of USSR. It was put into production in 1974.