Ctrl+F или ⌘-F

Literature review. One of the important factors in the formation of hydrocarbon deposits in the Ustyurt region is the
facies features of the Jurassic sequence, since the predominantly continental deposits of the lower, middle, and most of the upper
Jurassic are polyfacies. According to the experience of studying Jurassic formations similar in composition and origin in Western
Siberia, Southern Mangyshlak, Bukhara-Khiva region and, in fact, the fields of the Shakhpakhta step, the Sudoch trough, the best
terrigenous reservoirs are noted in channel facies, in facies of erosion incisions, coastal-marine and, less often , in lakes [1,8,9].
The Jurassic deposits are mostly represented by sandy-argillaceous subcoal-bearing formations, including lacustrine-
marsh, various alluvial (including channel) and coastal-marine deposits. Characterized by poor consistency of monolithic
sandstone layers, their lenticular character. The layers of the Lower Jurassic are relatively more consistent than the horizons of
the Middle Jurassic and have greater thicknesses. The reservoir properties of sandy-siltstone rocks in most cases turned out to be
low. Relatively high reservoir properties are characteristic of channel, including temporary flows, and coastal facies [4], which
depend on the material composition of rocks, their structural and textural features, the degree of sorting and roundness of clastic
O‘ZBEKISTON MILLIY
UNIVERSITETI
XABARLARI, 2022, [3/1]
ISSN 2181-7324
GEOLOGIYA
http://science.nuu.uz/uzmu.php
Natural sciences

Page 22

O‘zMU xabarlari
Вестник НУУз
ACTA NUUz
GEOLOGIYA 3/1 2022
- 260 -
material, the composition and type of cement, the nature of impurities, etc. P. These factors, in turn, are determined by the
distance of the feeding area and the hydrodynamic conditions of the sedimentation basin.
The lithological composition and the nature of changes in the section of the Lower Jurassic deposits indicate
insufficiently favorable conditions for the formation of highly promising reservoir rocks within the Ustyurt. But often there are
separate horizons of well-sorted sandy-silty reservoir rocks with high capacity and permeability (wells Zhies-1, East Aytuz-1,
Tlekuduk-1, Razlomnaya-1, Umid-1, Sulama-1, Western Aral- 1,2, etc.). Along with this, weakening of hydrodynamic conditions
favorable for the formation of seal rocks periodically occurred. Therefore, the occurring permeable formations are often blocked
by these tires, which are a reliable screen. The slow subsidence of the sedimentation basin, the absence of large elevations and
permanent water arteries did not contribute to the accumulation of thick sandy-silty sediments.
In the Middle Jurassic, sedimentation conditions change from alluvial and lacustrine-marsh to deltaic and coastal-marine.
This led to the frequent interbedding of sandy-silty layers and clay caps separating them. The layers are characterized by
discontinuous lenticular layering, erosion, wedging out, and changes in thickness. The thicknesses of the predominantly sandy
units vary from tens of centimeters to several meters. Permeable layers sometimes connect with each other, uniting into single
packs, sometimes they thin out to separate layers. In general, the Middle Jurassic deposits are characterized by the absence of
thick, consistent sandy layers.
Due to the significant role of transitional processes, the Middle Jurassic part of the section is the most complex in terms
of sedimentation. Discontinuous lenticular layering is widely developed here, with a mass of small intraformational
unconformities, erosion, pinching out, and changes in horizon thicknesses. This has led to a complex relationship between the
sand beds and the clayey-silty caps (“non-reservoirs”) separating them. At the end of the Late Jurassic, marine terrigenous-
carbonate rocks accumulated, forming another - terrigenous-carbonate formation. A characteristic feature of these formations in
Ustyurt is the absence of thick regionally and zonal clay seals within the formation itself. Here there are only covers of local
development. Tire thicknesses vary from 2-3m to 25m. Almost all types of thin bedding of sedimentary rocks are found in the
area under consideration, from plane-parallel to oblique, discontinuous, wedge-shaped, and lenticular [10].
The assessment of the oil and gas potential of Ustyurt based on the results of lithofacies, structural and geochemical
studies showed that the deposits of the Jurassic terrigenous formation are characterized by favorable factors for the generation
and accumulation of hydrocarbons, which have an increased residual generation potential (TOC = 0.72-0.93%, ( S1+S2)=0.6-0.9
mg HC/g rock). In the Early Jurassic, deposits with a generation potential accumulated throughout the study area. The Jurassic
complex of rocks has reached the main zone of gas formation in full.