Saatly Super Deep Well Sd1

The Saatly Super Deep well SD-1, with a proposed depth of 15,000 m/49,212 ft, was located within the Middle Kura Intermontane Depression (Kura Lowland), where the Kura and Araks rivers converge and the Mil and Mugan steppes join (Figure 1-5). It is a region of warm semi-desert and dry steppes with an arid climate. The average annual temperature is +10°C. Annual precipitation does not exceed 200-300 mm.

From December 1971 to August 1974, a preliminary well was drilled to 6,240 m/20,472 ft. The well penetrated Cenozoic molasse, Mesozoic Carboniferous deposits, and from 3,550 m/11,647 ft to bottom of the well, volcanogenic strata.

The Saatly Super Deep well was designed in accordance with a "Study of the Earth's mineral resources and super-deep drilling" conducted by the State Committee on Science and Engineering. The main goal of this program was to study the Earth's crust in the Mediterranean Alpine geosynclinal belt, including the following investigations:

1. A detailed study of solid, fluid and gaseous phases of the Earth's crust and their changes with depth.

2. The study of the geologic nature of seismic boundaries and the establishment of the reasons for crustal foliation by geophysical parameters.

3. The study of peculiarities of endogenic geologic processes manifested in deep parts of the Earth's crust, including the process of ore generation.

During the first stage of the investigations, while drilling the Saatly well to 8,000 m/26,247 ft, the main goal was to penetrate the sedimentary and volcanogenic section at a site of minimum thickness, according to geophysical study conducted in the area of Saatly local uplift. This was done (a) to study its composition, structure, occurrence, and oil content; (b) to study the conditions of generation and distribution of ores in the lower part of sedimentary-volcanogenic strata; (c) to penetrate granitic rocks, to study their interrelation with

Figure 1-5. Location of Saatly Super Deep Well SD-1. Distances: Baku to Saatly: 180 km (112 mi); Baku to Alyat: 72 km (45 mi); Alyat to Kazi-Magomed: 46 km (28 mi); Kazi-Magomed to Ali-Bairamly: 13 km (8 mi); Ali-Bairamly to Sabirabad: 38 km (24 mi); Sabirabad to Saatly: 12 km (7.5 mi).

sedimentary-volcanogenic formations; and (d) to develop and improve the drilling technology and methods of geological and geophysical investigations at great depth.

In this section the following stratigraphic units were penetrated (Figure 1-6):

Post-Pliocene (Quaternary) deposits (0-860 m) are represented by the irregular alternation of gray, thick-bedded clay; gray, unconsolidated siltstone; medium-grained and coarse-grained sandstone with grit inclusions; thin-bedded intervals with grit inclusions; and thin-bedded intervals of continental origin. Apsheronian Stage (860-1,930 m) is represented lithologically by alternation of sandy, silty and clayey rocks in the upper portion of

Age

Thickness, m

Column

Lithology/Petrography

Quaternary

Ve ■ 0 -

Shingles conglomerates, loams, sandy loams, sandstones, aleurites, clays

£

~ '_

Limestones, clays, aleurites,

£

1080

CL <

Akchagyl

350

Clays, aleurites, sandstones

Sarmat &

Middle

Pliocene

570

Sandstones, clays, aleurites, limestones

Jurassic Lower

710

coral limestones with sills of spilites

Cret.

L U L L L L L l_

Andesite Basalt

L It

L. tu

Andesite - Basalt

3 -5

^ *> & * h A ft /t

Dicritic porphyrite Andesite

Tuff aleurites Andesite - Basalt

Dacites

Figure 1-6. Stratigraphic section (from cores and logs) of Saatly Super Deep Well SD-1 (Modified after the Excursion Guide-Book for Azerbaijan SSR, Vol. I, 1984). Aleurites = siltstones.

Figure 1-6. Stratigraphic section (from cores and logs) of Saatly Super Deep Well SD-1 (Modified after the Excursion Guide-Book for Azerbaijan SSR, Vol. I, 1984). Aleurites = siltstones.

the section and with gray clay separated by silty, sandy and limy interlayers in the lower portion.

Akchagylian Stage (1,930-2,250 m) is composed of gray silty clay with rare and thin partings of polymictic siltstone.

Middle Pliocene (2,250-2,780 m) is represented by brown-gray silty clay alternating with polymictic sandstone.

Sarmatian Stage (2,780-2,830 m) is represented by alternation of thin-bedded sandy argillaceous rocks and carboniferous rocks, overlying Mesozoic carbonate. Cretaceous—Late Jurassic (2,830-3,529 m) is represented by the alternation of thick (200 m), fractured, pelitomorphic, siliceous metamorphosed limestone and volcanogenic intervals (5 and 54 m, respectively).

Jurassic (3,529-8,230 m) is represented by thick volcanogenic strata.

The main attention was paid to the composition, structure, physical properties, and geochemical attributes of volcanogenic rocks. Core samples from volcanogenic strata, studied petrographically in detail, give an idea of structure, composition, facies, and rock deformation of volcanogenic strata.

Volcanic facies on the SD-1 log are represented by two groups: (a) volcanic and (b) volcaniclastic. Volcanic facies are represented by a large number of genetic types, among which the leading ones are lava flows and lava breccias. Among rocks of the volcaniclastic facies, lavaclastites and hyaloclastites are widespread. Pyroclastic rocks (tuffs, tuff breccias), which belong to the same group of facies, are characterized by a variety of fragments, color, structure, and size. Volcanogenic-sedimentary facies in the section of Jurassic volcanogenic strata are represented by thin tuffs, tuffites, tufogene-sedimentary rocks (tuff sandstones, tuff siltstones). Intrusive units are represented only by non-abyssal (hypabyssal) facies, i.e., sills and dikes. In these strata, volcanogenic facies predominate over volcanic ones. The great thickness of volcanogenic strata testifies that the penetrated section is confined to the center of volcanic activity, in the region where a continuous supply of volcanic matter masks sedimentation.

According to petrographic data, volcanogenic strata changed from basalt to rhyolite. Most rocks belong to the porphyritic facies, and only a small group (dikes and sills) consists of aphyric basalt. In porphyritic rocks, plagioclase and magnetite are the main minerals. They are joined by dark-colored minerals, i.e., pyroxene, amphibole, and olivine. The contents of plagioclase, monoclinic pyroxene, amphibole, and magnetite in the main petrographic groups of rocks have been studied.

Porphyritic basalts and andesite-basalts are very similar to each other in the content of all rock-forming minerals. Plagioclase is present in both and its content is approximately equal to that of bytownite-

anorthite. Clinopyroxenes are represented by subcalcic ferrous augites, characteristic of geosynclinal sequences of normal alkalinity. It is supposed that hyperalkalinity, sometimes noted in these rocks, is allogenic. The presence of amphiboles in hornblende-andesite and zeolitic metasomatites shows the volcanic origin of replaced rocks.

The data obtained from chemical analyses prove the association of volcanics with basalts, andesite-basalts, andesites, andesite-dacites, dacites and rhyodacites. According to silica and alkaline oxide ratios (Na2O/K2O), basalts, andesite-basalts, andesites, and dacites belong to the limestone-alkaline gradation. Basalts and andesite-basalts are characterized by a high content of aluminia and low content of silica. In general, the composition of basic rocks of volcanogenic strata corresponds to that of the high-aluminiferous basalts of the andesite-basalt series.

Acid and intermediate rocks are characterized by a low alkali content. Na2O predominates over K2O. High content of Na2O both in the basic and acidic volcanics is due to autometamorphism. Low content of TiO2 and low content of Fe2O3+FeO point to the geosynclinal nature of basalts. Analyzed rocks, on the whole, are characterized by the low content of SiO2, Fe2O3+FeO, MgO, TiO2, and K2O, and high content of Al2O3 and Na2O.

Volcanogenic rocks can be differentiated on the basis of certain structural features. Rocks of the upper and middle parts of volcanogenic strata are of geosynclinal andesite-basaltic type, analogous to the Middle Jurassic (Bathonian) sequence, occurring within the Lesser Caucasus.

Rocks of the lower part of the section cannot be determined beforehand because their lower boundary was not penetrated. As acidic volcanics predominate in the section, the rocks can be identified as sodic rhyolites. It is possible that at deeper horizons the volcanics of basic composition are present; then, the sequence can be identified as basalt-andesite-rhyolitic, analogous to the Lower and Middle Jurassic sequence of the Lesser Caucasus.

All the rocks of volcanogenic strata are metamorphosed. Secondary minerals replace volcanic glass and primary minerals, and also infill cavities and fractures. Metamorphic minerals form varied mineral associations, among which are clay minerals, chlorite, calcite, chalcedony, quartz, albite, zeolite (laumonite), hematite, leucoxene, sphene, prehnite, epidote, pumpellyite, and sulphides. Acidic rocks, which compose the lower part of the strata, are silicified and calcitized.

In the lower part of the section some secondary minerals as quartz, chalcedony, sericite, and epidote are added to chlorite and calcite. With increase in depth, the low-temperature zeolites are replaced by more high-temperature epidote and then by prehnite-pumpellyite (greenschist stage of metamorphism). A low-temperature calcite-chlorite is also developed. A geochemical trend of main chalco-lithophylic elements in volcanics coincides with that in calcic-alkaline extrusive series of island arcs.

Geochemical regularities in distribution of rare elements in rocks of volcanogenic strata correspond to those in volcanics, originated in zones of island arcs. In the SD-1 well section, the degree of helium preservation in volcanics is lower than in terrigenous deposits of the sedimentary sequence. Geochemical analyses of gases dissolved in interstitial solutions and/or adsorbed in the rocks, showed that the main components of gases emanating from volcanic rocks are carbonic-acid, nitric-carbonic-acid, and hydrocarbons. The main hydrocarbon gas is methane.

According to the results of gravity and magnetic surveys, the region of the Talysh-Vandam gravity maximum is structurally heterogeneous. Different areas of maxima (anomalies of the second order) are of different origin in the Earth's crust. In the subsurface structure of the Saatly-Kyurdamir maximum, the projection of Pre-Alpine basement is interpreted as the complex of Upper Archean and Lower Achean sequences with allochtonous features. In the Alpine complex overlapping basement, products of Mesozoic magmatism of basic and intermediate composition are developed.

During the second stage of drilling (below 8,000 m), it is expected that the SD-1 well will penetrate magmatic rocks of Mesozoic or older age; below 10,000 m, the older basement metamorphic rocks are expected. Saatly SD-1 well is one of the first wells which will penetrate rocks of great depth and answer many questions.

Scientific and practical findings from the first stage of drilling the SD-1 well are the following:

1. The Earth's crust section 8-km thick has been penetrated. This section is a standard not only for Saatly-Kyurdamir buried uplift, where commercial oil is produced from the volcanogenic strata, but also for the whole Alpine zone of the southern part of the Transcaucasus, where deposits of the most important commercial minerals are located.

2. The volcanogenic section penetrated by the well is 5,000-m thick, which contradicts the existing opinion that the sedimentary-volcanogenic section overlying the Saatly local uplift is thin.

3. Microfauna (radiolaria) present at a depth of 6,560 m in siliceous tuff siltstones point to the deep accumulation of volcanogenic material of Jurassic age. This changes the existing opinion on the tectonic-magmatic evolution of the region reflecting the geosynclinal regime of the Transcaucasus Median Masiff development.

4. The results of petrochemical and geochemical study of the volcanics and the distribution of rare elements in the deposits show that they have been derived from calcic-alkali magma of the same source formed in island arc zones.

5. According to the prognosis, within the Kura Depre ssion the temperature must rise by 2-2.5°C per hundred meters of depth. This prognosis was not confirmed. At a depth of 8 km, the temperature reaches only 140°C. Such a low temperature at great depth is caused by low heat flow from the interior of the Earth's crust due to tectonic-magmatic evolution of the region.

CHAPTER 2

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