Download LITHOLOGY - mineralogical features NONCONVENTIONAL

LITHOLOGY - MINERALOGICAL FEATURES NONCONVENTIONAL
RESERVOIR (WEST SIBERIAN PETROLEUM PROVINCE)
L.M.Sitdikova, V.G.Izotov, N.M.Khasanova, N.M.Nizamutdinov, E.U.Sidorova, M.P.Zaripov,
R.A.Khasanov
Kazan Federal University, Institute of Geology and Petroleum Technology, Kazan, RUSSIA
E-mail: [email protected]
Now development of easily accessible hydrocarbon reserves is included in the final stage. There is a
need of search of new reserves of their gain. Essentially new type of a source of hydrocarbon raw
materials is revealed. It is connected with low-porous "shaly" argillaceous rocks - mudstones,
siltstones. One of such objects is the rocks of the Bazhenov suite. Bazhenov Formation is one of the
most perspective horizons [2] for the West Siberian oil and gas province. This Formation serves as the
main fluid sealing rocks territory. At the same time, it is a regional oil generating horizon of the West
Siberian oil and gas province.
Bazhenov formation is widespread on most parts of the province. A number of fields of hydrocarbons
of Western Siberia are connecting with this horizon: Nivagalsky, Uryevsky, Las-Egansky, Southern
Pokachevskoye, Pokachevsky, Kluchevoe, Kechimovsky, and are being in commercial production.
Industrial oil-and-gas content is connected with deposits of verkhneyursky, achimovsky and
neokomsky oil-and-gas complexes.
Hydrocarbons are mobile systems and preservation of deposit is determined by the stability fluid
sealing rocks horizon [1]. In this regard detailed studying by a complex of methods of geological and
mineralogical features of rocks of the horizon is necessary.
Objects and experimental results
The macro structural and textural characteristic of rocks plays an important role in studying of
oil-and-gas complexes. It provides information about the paleo geographic, hydrodynamic
conditions of formation of reservoirs and fluid sealing rocks. Characteristics of core samples
depend on these conditions: lamination type, layer thickness, relationship with other types of
rocks and mineralogical characteristics.
Based on these studies, it was found that greatest distribution have clay and argillaceous rocks
that form homogeneous strata texture (fig. 1a), as well as horizontal lamination with
allocations of a marlaceous material (fig. 1b).
Fig.1а. Bituminous mudstone interbedded Fig.1б. Mudstone with bituminous marly
with mudstone silty.
secretions.
Areas rocks are characterized by uneven distribution of clay and marl plots (2a. 2b). Often in
the composition of the rocks of the Bazhenov suite carbonate-clay material reaches 40-50% of
the total volume of the rock. Thin lamination reflects seasonal variations in the process of
sedimentation.
Fig.2а. Carbonate rock pelitic bituminous.
Fig.2б. Bituminous carbonates mudstone.
Data of optic-microscopic researches testify that rocks of the Bazhenov suite are a difficult
lithology-mineralogical complex. For them variations in the maintenance of fine mineral
phases and larger particles are characteristic (fig. 3a, b).
Fig. 3а. Thin - roughly layered aleurolite
(puffs of mm dimension with smooth
transitions one to another).
Fig. 3б. Thin-layer aleurolite with fine quartz
and carbonate material.
The most important component of the rocks is clayey material for the study of which was
attracted by X-ray diffraction patterns method. According to experimental studies, it was
found that the clay components of the Bazhenov suite in all the samples studied are complex
associations of clay minerals. The most common clay minerals: illite, kaolinite, chlorite,
mixed-base complexes illite-smectite minerals as well as finely divided quartz, calcite,
feldspar (Fig. 4).
Fig. 4 XRD pattern of the air-dry sample.
Quantitative relationships of the leading clay minerals of the Bazhenov suite are connected
with distribution of the main types of rocks and with sedimentation conditions. Variations of
quantity of a fine component are noted. According to the RFA-analysis it is established that as
a part of the Bazhenov suite there is a large number of clay minerals with difficult structure.
These minerals may be active catalysts for conversion of simple hydrocarbon phase (methane,
ethane, propane) to more complex hydrocarbon phase. In interlayered intervals of clay
minerals special thermodynamic conditions can be created. They are favorable for the
synthesis of complex petroleum hydrocarbons, by entering into the formation of simple
hydrocarbons. This confirms the position that the Bazhenov suite is a oil generating horizon
[3].
Another perspective method of studying of rocks reservoir and fluid sealing rocks is the
electronic paramagnetic resonance (EPR). This method allows studying the characteristics of
various chemical elements entering into the structure of minerals including clay. The obtained
results allow characterizing the conditions of formation of deposits. In samples with a clear
alternation of puff, have been studied separately dark and light-gray seams. For the layers of
dark color characteristic of the EPR spectra of vanadyl groups VO2+ and for light - spectra
characteristic of manganese Mn2+ in calcite
(Fig. 6).
Fig.5. EPR spectrum (scan magnetic field 80
mT) of core samples from black and white
layers. R line due to organic radicals, VO2+
vanadyl ions associated with porphyrin
species [4], manganese Mn2+ ions in the
structure crystals of calcite [5].
Fig. 6. EPR spectrum of organic radical with scanning magnetic field 10 mT from black and
white layers of core samples before and after dissolution in CHCl3; thermal treatment at 350
and 600 0C.
Ion radical SO3- associated with carbonate structure, E’ – radical associated with defects in
quartz structure.
Conclusions
Performed analysis by electron paramagnetic resonance allows revealing elements of markers
indicating the leading role of organic matter directly to the formation of the Bazhenov suite.
Such elements include vanadium, which relatively high concentrations at rocks are associated
with organic matter [6].
On the other hand, an element such as manganese is an indicator paleogeographic conditions
and humid conditions sedimentation [7]. Frequent differentiation layers, points to uneven
distribution of organic content. This may be due to changes often depositional environments
that characterize the rhythm of formation layers. This rhythm is consistent with the annual
climate variations.
Research showed that the Bazhenov suite is a complicated geological formation, as evidenced
by its variable mineral composition. Bazhenov oil source is oil generating strata due to the
presence of mineral catalysts for (illite, mixed-minerals, to a certain extent - kaolinite)
transformation of simple hydrocarbon phase to complicated. Bazhenov suite was formed in a
relatively shallow (100-150 m) at sufficiently moderate ambient temperature conditions of the
pool.
Thus, nonconventional collectors of oil are rocks of Bazhenov suite. Formation of oil deposit
of was necessary to have reservoir - collector and existence of fluid sealing rocks. Rocks are
considered as of oil generating and containing abnormally high amount of the transformed
organic substance – kerogen from which it was generated either viscous oil, or bitumen, or
carbonaceous substance.
References
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horizons as a factor in the successful development of hydrocarbon deposits in the late stage of
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povysheniy effektivnosti razrabotki mestorogdenii na pozdnei stadii” – Kazan: Izd-vo «Fen»
AN RT, (in Russian) 2013. – С. 203-204.
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свиты Западной Сибири. (in Russian) - M.: Nauka, 1984. – 36 c.
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West Siberian Jurassic deposits. Int.J. of Science Georesources. 2012. Vol. 1 (12). P.11-14.