shows of geothermal and hydrogeological factors in oil and gas deposits

Dr.A.Javadova 1

North & Central Caspian- Kazakhstan

Shows of geothermal and hydrogeological factors in oil & gas deposits

Key points

I. Regions of stable and long immersion where high thicknesses of clayey series with an

increased concentration of a diffused organic matter accumulate, are rather favorable for oil

and gas formation.

II. In the interval of 65-120° temperature and the pressure of 100-200 atm a main phase of oil

formation becomes apparent (Vassoyevich and others, 1969) during which HC generation

occurs.

III. With a further development of the process HC migration starts from the zone of generation

into the porous formations-reservoirs where they enter the warmed-up water environment.

Then, together with it, they provide a total water-pressure system and continue the lateral

intra formational migration to the oil and gas accumulation sectors.

IV. The region of oil and gas accumulation and formation of HC deposits is located on the

hypsometrically uplifted sectors and gravitates towards to the positive structures.

Dr.A.Javadova 2



Key points

V. They are characterized with a high tectonic activity along almost the whole geological history of

the Aralo-Caspian region’s development and a wide development of fractured and dome

tectonics.

VI. There are also vertical overflows of fluids (water-HC) tied to the phenomenon of an elastic

water yield and the total high hydrostatic and geodynamic potential of water-pressure

systems (especially in the central regions of major troughs). High speeds of vertical overflows,

comparing to the lateral migration, provide the inflow of HC-containing fluids from the troughs to

its peripheral parts and the zones of uplifts.

VII. Presence of oil-sourced suites- clayey-siltstone rocks is widely spread in the inner parts of the

troughs named.

Dr.A.Javadova 3



Conclusions

• The processes of oil and gas accumulation, formation and HC deposits’ preservation, from

one side, are determined by the presence of formations-reservoirs and transporting

(mainly, water) environment, and from another one- a development of thick and stable

water-oil-gas- non-permeable seals.

• Such seals within the PriCaspian depression are a thick salt-bearing series of Kungur;

clayey and marly-clayey series of Upper (and partially Middle) Jurassic; Neokom;

Aptian, Upper Cretaceous and Paleogene.

• All these series, except for the salt-bearing one, are widely developed within Kazakhstan

(being absent only in the most uplifted zone of C.Mangyshlak, Ustyurt and others).

Dr.A.Javadova 4



Conclusions

• It should be noted that in the area of mountainous-folding zone of Uralo-Mugojar and Karatau an

intensive seepage of atmosphere waters occurs. These waters possess a high oxidizing potential

destructing HC deposits. Therefore, close to these zones an oil-gas destruction occurs. The

processes of oil and gas accumulation and oil and gas destruction either occur simultaneously or

change each other in time determining a prospectivity level of areas on oil and gas during a certain

geological age. But it is important that positive structural elements which are located inside

depressions and troughs are moved away and isolated from seepage regions.

• Reformation of organic matter in the rocks, oil and gas formation, accumulation and keeping of HC

deposits occurred with a constant participation of formation waters in all geological ages. This

allows differing in the complex of prospecting criteria 2 groups of shows of oil and gas content

prospects: hydrogeochemical and geothermal ones.

Dr.A.Javadova 5



Hydrochemical shows (tied to hydrochemical and hydrodynamic conditions).

• There are 2 major hydrodynamic regions within the C.& N.Caspian: the first one covers

formation waters occurring in the environment of deep closing of bowels in the central parts of

the Pri Caspian depression and major troughs of onshore Kazakhstan. These are preliminary

oil- gas- forming waters and are characterized with a high salinity, calcium chloride

hydrochemical type; high level of metamorphization and non-sulphate content;

increased content of organic acids, ammonium, bromine, iodine, potassium, calcium and

have an acid reaction. Their gas content lacks acid gas components- the products of

oxidation-reduction reactions of initial stages of diagenesis (CO2, H2S). Their formation in

the conditions of high temperatures and pressures conditions a high gas saturation; and closing

of bowels- absence of elasticity deficit (saturation).

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• With a higher sinking depth and occurrence of most optimal thermodynamic conditions for HC

generation content of dissolved methane gases enriched with heavy HC, organic nitrogen

and helium increases. While natural discharge to the daily surface or overlying water-bearing

horizons these waters change their initial shape. In an unaltered manner they can be stripped only

with deep wells.

• In the region covering the territories close to regional zones of uplifts and on the ends of

troughs, intensive and considerable water change formation waters have a seepage genesis and

become one of the strongest factors of destruction (oxidation) of HC deposits. This process brings

to formation of secondary oil waters with a comparatively increased salinity, a

metamorphization, an increased sulphate content and a decreased content of

microelements- iodine, potassium, and others.

Dr.A.Javadova 7




• Based on hydrochemical type, they vary from calcium chloride and chlore-magnesium to sulphate-

and hydrocarbonate-sodic ones. They contain dissolved gases of different content and different

elasticity level, often with a saturation deficit, enriched with nitrogen, carbonic acid, hydrogen

sulphide etc. (biogenic nitrogen with an admixture of the atmosphere one). Anaerobic bacteria,

reductioning sulphates and oxidizing HC are widely developed. Also, there are naphthenic acids and

phenols are occurring. Reduction of sulphates on the contour of oil deposits leads to an increased

content of sulfur in oils and increase of their gumminess and specific weight.

Dr.A.Javadova 8



Geotermal shows

• Thermodynamic analysis of thermal processes in water-pressure systems of Mangyshlak-Ustyurt oil-

gas- bearing province evidences about their adiabatic iso- and non-iso-entropic character. Iso-entropic

character is typical for the heat-mass transfer in the lateral plan whereas intraformational vertical heat-

mass transfer occurs along the non-iso-entropic way is an irreversible process. Then, according to the

total correlation of thermodynamic of irreversible processes mass transfer occurring in the direction

opposite to geothermogradient (in the direction of temperature decrease) leads to warmth formation,

increase in density of a heat flow, a change in a heat conductivity and thermogradient.

• Presence in the geological section of rocks mixed by their thermal-physical properties, presence of a

convective heat-mass transfer of descending (seepage of cold atmospheric waters) and ascending

directions (discharge of high formation temperatures from bowels) and, also, localization of oil and gas

deposits and high gas saturation of formation waters of the region bring to an essential complication of

the curve in thermogradient change with depth.

Dr.A.Javadova 9



Geothermal shows

• Thus, in the PriCaspian depression curve of change of geothermogradient with depth, as a whole,

has a concave shape relative to the axis of depths with a minimum meeting the interval of occurrence of

heat-conducting salt-bearing series of Kungur or with its absence of a water-conducting series (Albian-

Senomanian, Jurassic and others). On Mangyshlak, Ustyurt and N.PriAral thermogradient has a

concave-convex shape characterizing a distribution of temperature over the section: concave part of

thermogram evidences about cooling of the upper part of the section up to 750 m with cold seepage

waters and decrease of the value of thermogradient; the lower part reflects a warming-up of the section

at the account of delivery of deep, often convective heat.

• An important peculiarity of total geothermal conditions of the region is, from one side, commonality in

temperatures’ distribution with the positive and negative elements of structures in the PriCaspian

depression and Turanian bed (Kazakhstan), and from another one- a higher thermal regime of the oil-

and gas- formation zones within Mangyshlak, Ustyurt, and NW PriAral.

Dr.A.Javadova 10



Geothermal shows

• It is important to mention that HC phase condition shows that oil and gas are generated with the

temperatures up to 100°, light oil and gas- at up to 125°, gas primarily- at up to 150°, and only gas-

higher than at 150-175°. With a temperature of more than 150-175° oil deposits, due to a

destruction of oil and formation of gas-condensate and methane, cannot exist (Lindtpon, 1968-69,

Neruchev- 1967 and others). But in PreCaucasus oil deposits at 3800 m depth have a 180°

temperature (Tkhostov, 1972) and in USA oil deposits are found in the traps with 183-200°

temperature (Storer, 1969). Using the given values for geothermal data at different phase conditions

of HC deposits we can mention depths and thickness of main stages for liquid and gas HC

generation and the area of their potential disclosure.

shows of geothermal and hydrogeological factors in oil and gas deposits

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