Volume 04 Issue 02-2022
23
The American Journal of Engineering and Technology
(ISSN
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2689-0984)
VOLUME
04
I
SSUE
02
Pages:
23-36
SJIF
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(2020:
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)
(2021:
5.
705
)
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1121105677
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–
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ABSTRACT
In this article, it considered on the oil and gas potentiality of the southeast part of the Bukhara-Khiva region. Also
analyzed the issue of the prospects for the oil and gas potential of the Lower-Middle Jurassic deposits within the
Beshkent trough and have not yet been finally clarified. In the Shakarbulak area, only the uppermost part of
terrigenous deposits, represented by impermeable rocks, was exposed.
KEYWORDS
Reservoir, reservoir, formation, horizon, rocks, zone, well, opening, section, inflow, flow rate, porosity, fracturing,
hydrocarbon, gas saturation, oil saturation, reef, limestone.
INTRODUCTION
The Shakarbulak field is located in the Beshkent oil and
gas bearing area, within which Aknazar, Kapali, Novy
Alan, Girsan, Kirkuloch, North Nishan, Kamashi,
Beshkent, Zafar, Shurtan, North Shurtan, Buzakhur
North Guzar, Garmiston and Kumchuk fields have so far
been identified.
Research Article
ON THE OIL AND GAS BEARING CAPACITY OF THE SOUTHEASTERN
PART OF THE BUKHARA-KHIVA REGION
Submission Date:
February 11, 2022,
Accepted Date:
February 18, 2022,
Published Date:
February 28, 2022 |
Crossref doi:
https://doi.org/10.37547/tajet/Volume04Issue02-06
Khaitov Odiljon Gafurovich
Candidate of Geological and Mineralogical Sciences, Assistant professor, Head of the Department of
Mining At the Tashkent State Technical University named after Islam Karimov, Uzbekistan
Journal
Website:
https://theamericanjou
rnals.com/index.php/ta
jet
Copyright:
Original
content from this work
may be used under the
terms of the creative
commons
attributes
4.0 licence.
Volume 04 Issue 02-2022
24
The American Journal of Engineering and Technology
(ISSN
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2689-0984)
VOLUME
04
I
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02
Pages:
23-36
SJIF
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(2020:
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(2021:
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705
)
OCLC
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1121105677
METADATA
IF
–
7.856
Publisher:
The USA Journals
Of these, the last six fields, as well as the eastern
section of Shakarbulak field are located within the
Upper Jurassic barrier-reef system and in the
associated zone of spreading of zarif facies (facies of
closed shelf). All other deposits are located in the zone
of distribution of depression faces (XV-DERF) and
underlying facies of the open shelf (XV-PR, XV-
horizons). The western section of the Shakarbulak field
confined to the same zone.
Of the listed fields, only one is purely oil Garmiston),
three (North Shurtan, Kumchuk, Shakarbulak) are gas-
condensate oil fields; all others are gas-condensate,
including the largest in the republic Shurtan field.
The question about the prospects of oil and gas
bearing capacity of Lower-Middle Jurassic deposits
within the Beshkent trough been definitively clarified
yet. In the Shakarbulak area, only the uppermost part
of
terrigenous
sediments,
represented
by
impermeable rocks, has been uncovered.
Cretaceous deposits within the Beshkent trough are
unpromising.
Industrial oil and gas content of the western part of the
Shakarbulak area established by sampling in the
production casing of well one of horizons: XV-PR and
XV-DERF. From all six intervals, tested in this well,
rather significant flows of liquid hydrocarbons with
flow rates from 10.6 to 96.4 t/sec and gas with flow
rates up to 600 thousand m3/sec received, that was
unexpected for the section penetrated by the well, as
there are almost no collectors with corresponding
permeability and porosity in it.
According to GIS data, pore-type reservoirs in the
section of Well 1 are predominantly distributed in the
XV-a horizon and occur in the form of layers and
bundles from 0.6 to 4.4 m thick among compacted
limestones. Their total thickness is 12.4 m with a total
thickness of 37 m, and porosity - 8-9.5%, except for two
interlayers and the roof part of the horizon, the
porosity of which clearly exceeds the conditionality
boundary of reservoirs, set at 8%. Obtaining of 45.5 m3
per day from the first interval (3785-3772), where only
one bed of 3 m is distinguished and porosity of 8.5 %,
with a daily flow rate on 4-mm pipe. Indicates
fracturing, as according to petrophysical dependence,
represented reservoir capacity with 8.5 % porosity is
only 1 mlD, whereas its calculated value according to
different modes of testing is 36 mlD. The second
interval of perforation (3769-3746 m) is the rest of the
XV-a horizon, and this produced oil with 68.9 m3 of gas
[1-12].
XV-PR horizon in the section of well №1 is represented
mainly by clay limestone. Among which according to
logging data are thin (0.6-1.2 m) interlayers of porous
reservoirs with porosity from 6 to 10%, with total
thickness of 12.2 m at total thickness of 58 m, and only
6.4 m from them are oil-conditional (with porosity of
8% and more). Most of the latter are concentrated in a
narrow (14-meter) interval, not covered by the theme.
In the lower interval of perforation (3739-3727), which
gave oil, there is one 0.8 m thick interval with porosity
of 8.5% and two with porosity below conditionality
(6.5-7%), with a daily oil flow rate of 60.2 m
3
per 5 mm
unit.
The upper perforation interval, which gave gas flow
rate up to 488 thousand m
3
/s and hydrocarbons (oil
with condensate) up to 15 m
3
/day is represented only
by dense clayey limestones with porosity 1% according
to rock samples taken from the roof part of the XV-PR
horizon and the underlying part of the upper lying
horizon (XV-DERF).
The latter is represented by dense clayey-carbonate
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bituminous rocks stratified by relatively clean
limestones with porosity up to 5% and permeability of
less than 0.01 mld in the matrix, up to 4 mld in fractures
(according to core laboratory tests). Only in the roof
part of the horizon, directly under the lower anhydrites
of the Cimmeridge-Titon, according to GIS data, there
is a porous reservoir layer of 0.8 m thickness and
porosity of 10%, which is traced everywhere within the
western part of the assessed area, as well as in the
neighboring Zafar and Mangit areas. It is covered by
sampling of the last perforation interval (3680-3670
m), which yielded gas flow rate of 89 thousand m
3
/s
and liquid hydrocarbons flow rate of 25.9 m
3
/s at 6-mm.
Thus, at the western (no-reef) section of Shakarbulak
area by sampling of well №1, commercial oil and gas
content of the entire upper half (112m) of carbonate
strata, starting from the top of the XVI horizon (the
latter was not covered by sampling) was established.
Exactly the same stratigraphic range of gas content
established earlier at the adjacent Zafar gas-
condensate field.
The results of well №1 test unambiguously indicate
wide development of fracturing in the section of the
carbonate formation penetrated by it. However, the
performed complex of GIS and data of core analysis,
selected in limited volume, do not allow distinguish in
the section of productive formation the distribution
and parameters of rock fracturing [13-19].
Well № 3, drilled in the vaulted part of the dome,
concealed a generally similar section, but differing
from the section of well №1 in the absence of pore-type
reservoirs with porosity of 8% or more in the XV-PR
horizon, as well as a slightly lower distribution of such
reservoirs in the XV-a horizon. At the same time, all
horizons of the carbonate formation were penetrated
at higher levels than in well №1, which gave commercial
flows of oil and gas from all perforated intervals
without exception, with good quality of production
string fastening (according to acoustic cement meter
data). However, commercial gas inflow with
condensate obtained only from the roof horizon XV-
DERF, represented by pore-type reservoir with
porosity of 9.5 % and thickness of 1.2 m. Of the six
sampled intervals in sediments XV-PR, XV- a and XVI
horizons, only two (one in each of the first two
horizons) received weak water inflows with minor oil
and gas occurrences in the upper interval of
perforations XV-PR horizon. From the other intervals,
(one in the XV-PR and XV-a horizon, two in the XVI
horizon) inflows not obtained. At the same time,
according to GIS materials, pores identified in the XV-a
horizon and covered by sampling characterized as
productive.
The section cut by well № 6 Zafar almost completely
repeats the section of well №3, while all tested
intervals (one each in XV-DERF and XV-a and 3 in XV-PR
horizon) yielded no flows, including the top layer of XV-
DERF horizon with porosity of 8%.
At first glance, it seems that the reason for the
negative results of sampling wells 3-Shakarbulak and 6-
Zafar is the absence or weak development of
fracturing in the sections penetrated by them.
However, analysis of geological and technical
conditions of wells drilling allows us to put forward a
different version. First, let us consider the data on well
№1, which gave commercial flows from all tested
intervals and regardless of its presence in the intervals
of perforated reservoirs with high porosity: the upper
part of carbonate formation, including XV-DERF and
Volume 04 Issue 02-2022
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VOLUME
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Publisher:
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XV-PR horizons, passed in the solution density of 1.2
g/cm
3
. From the depth of 3747 m the sinking was
carried out on a light mud with density of 1.07 g/cm
3
,
because at this depth (top of XV-a horizon) the
absorption of mud began. Thus, XV-a and XVI horizons
were opened almost at equilibrium with formation
pressure, and the upper part - with repression 47
kg/cm. In the same mode (with repression of 7-13 kg)
the completely productive formation (XV-DERF, XV-PR,
XV-a horizons) was penetrated by well №.1 - Zafar,
which was the discoverer of Zafar gas-condensate field
(1). Obviously, at such mode of productive stratum
penetration the safety of fracture channels from clay
mud penetration and subsequent plugging by solid
components of flushing fluid ensured. All other wells
drilled with weighted solutions, in which the fractures
could be sealed with clay particles. Obtaining flows of
formation fluids from such objects in the process of
subsequent testing depends on block permeability of
reservoir, depth of filtrate penetration of flushing fluid
and residual oil and gas saturation in the zone of
penetration. At the same time, these data do not prove
the presence of fracturing (only open fracturing
meant) in the sections of both wells.
Given the ambiguity of the solution of the issues
considered by the above data, it is necessary to
consider other aspects with the actual materials on
Mangit area. Within which the wells opened sections of
carbonate strata, similar to the sections of wells №
three and six (Zafar). However, at much higher
elevations in the absence of structural separation,
which could provide isolation from the oil deposit of
the western part of Shakarbulak area.
As a result of interval sampling of XV-a, XV-PR and XV-
DERF horizons in wells №№ 2,3 and 4 from all intervals
of perforation (except for one in well № 2) there were
received inflows of formation water with weak oil
manifestations, or weak oil inflows (their two top
intervals of well № 4). In three cases, (two in well №4
and one in well №3), there was an overflow of 8 to 18
m/day, while in the remaining cases weak inflows were
obtained.
The above data indicate that the results of sampling
the wells of the Mangit area FES of the section
penetrated by them, despite the use of dense solutions
(1.44-1.48 g/cm
3
). when drilling them, which is
explained by abnormally high reservoir pressure
established in this area, at which the calculated values
of repression on formation were lower than in wells №
3 and 6 (Zafar).
Water saturation of reservoirs uncovered in the Mangit
area at higher elevations than in the western part of
the
Shakarbulak
area
clearly
explained
by
hydrodynamic isolation of this area from the evaluated
one, which characterized by the lowest hydraulic
potential compared to the adjacent areas. The Zafar
area
in
hydrodynamic
respect
occupies
an
intermediate position. The hydraulic separation of the
latter from both the Mangit and the assessed area
caused by a discontinuity limiting this area. The nature
of the hydrodynamic separation between the Mangit
and assessed areas seen to be different, since the
presence of a high-amplitude discontinuity between
them is unlikely.
The paleo-structural map of the roof of the XV-PR
horizon shows that the Shakarbulak area before the
structural reorganization of the latest stage of folding
is a relatively large brachiiform fold with an amplitude
of 150 m. Recent data on the Ichki, North Umid, and
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–
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Marjon fields (2) indicate the presence of
epigenetically sealed oil deposits in layered sections of
the Upper Jurassic carbonate sequence of the
Chardzhou tectonic stage, the contours of which
controlled by the paleostructural plan, namely the
trailing paleoisogypsum. Their sealing in the VPC zone
ensures the preservation of such deposits after
structural reorganization by epigenetic and mineral
formation. By analogy with the above deposits one
may assume the formation of multilayer oil deposits in
deposits of the productive strata (XV-DERF, XV-PR, XV-
a) of the evaluated area, with the formation of sealing
zones near the closing isohypses. With the only
difference, that higher tectonic activity of the latest
stage in this area and intensive fracturing associated
with it could lead to their piriform formation into a
single massive type, which we observe now.
At the same time, the fractured rocks as well as the
block permeability of pore-type reservoirs were
preserved here due to the preserving role of
hydrocarbons whereas in the outline zone (the paleo-
contour is meant). The formation of secondary
materials could lead to complete healing of fractures
and conductive pore channels, at least, to a sharp
deterioration of the permeability of the entire section
of carbonate hummocks.
From the position of the stated mechanism of
formation of an impermeable zone separating the
evaluated area from Mangitskaya area, the absence of
flows from all tested intervals in well №6 - Zafar, which
is not located in this very zone, becomes explainable.
Negative results of sampling ХV-PR and XV-a horizons
in well №3 can be explained by their penetration at
high underbalanced formations (71-79 kg/cm
3
).
The non-triviality of the question about the phase state
of hydrocarbons in the deposit is visible at least by the
fact that in the documentation of the results of
sampling of well №1 in all cases the received flows
characterized as “oil with gas” or “gas with oil”.
Meanwhile, the uppermost sampling interval 3680-
3670 m (XV-DERF), judging by the value of the gas
factor, exceeding 4 thousand m
3
/t, is a gas condensate
object, and the liquid production of the well,
apparently, contained an admixture of darker than
condensate oil.
Values of the gas factor for the lower three test objects
(XV-a and the lower part of the XV-PR horizon) at small
junctions are 426-521 m
3
/t, which is an order of
magnitude lower than in the upper horizon and
indicates the oil saturation of the tested intervals.
Contradictory data obtained from intervals 3697-3690
and 3696-3686 m, which practically represent the
same test object. However, they differ sharply in the
nature of the obtained production: the lower interval
gave gas with a flow rate of 300 to 600 thousand m
3
/s,
with a small content of liquid hydrocarbons, and the
upper - production with an inverse ratio of liquid and
gaseous hydrocarbons. Formation oil samples in well
№1 not taken due to watering of production.
Well №3, when testing the upper part of the XV-DERF
horizon, gave a gas-condensate inflow, similar in the
ratio of liquid and gas HC to the test data of the
uppermost interval of well №1. The gas-condensate
surveys performed at this site confirmed this. Wells
have not penetrated VNK in the considered section of
the evaluated area. It is impossible to determine the
position of the gas-condensate complex based on the
data of well №1, because of the great remoteness of
Volume 04 Issue 02-2022
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VOLUME
04
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Pages:
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SJIF
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(2020:
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)
(2021:
5.
705
)
OCLC
–
1121105677
METADATA
IF
–
7.856
Publisher:
The USA Journals
the perforation intervals, which gave gas and oil; it is
not traceable by the materials of GIS (geographic
information system).
In connection with the above, we used piezogram of
the Upper Jurassic productive reservoir to determine
VNK and HNK. High accuracy of reservoir pressure
registration, performed by Caster manometers,
allowed us to obtain reliable information on pressure
changes throughout the height of productive
reservoir. Measurements filled in nine intervals of well
№.1 and one interval of well №. 3 were perfectly laid on
two straight lines, intersecting in a point with a mark of
minus 3271 m, corresponding to a mark of GOC.
Elements I and II characterize, respectively, the gas-
condensate and oil parts of the reservoir. Their
different angles of inclination to the axis of absolute
marks “reflect the density of reservoir fluids,
numerically equal to the tangents of these angles and
equal to 0.532 g/cm
3
in the gas-condensate part of the
reservoir and 0.708 g/cm
3
in the oil-saturated interval.
The high density of gas in formation conditions, more
than two times higher than the calculated value
determined by the composition of reservoir gas and
equal to 0.25 g/cm
3
, is noteworthy. Such a discrepancy
explained by the presence of residual mobile oil in the
pore space of the gas-condensate part of the reservoir.
To confirm this, it is necessary to select and examine
the sealed core. Failure to account for residual oil can
lead to a significant overestimation of gas reserves (4).
Lack of data on reservoir pressure of the water-
saturated part of the reservoir in the western part of
the evaluated area does not allow to build a
corresponding peplum and by it to determine KOC for
this area. Nevertheless, attraction of data on the
eastern part of the field allowed completing the
piezogram of the reservoir for the whole area,
including the water-saturated part. At the same time,
the information about formation pressures in this area
supplemented with data about the positions of VNK
and GNK, established on the materials of GIS,
respectively, at levels minus 3388 and 3327 m. As can
be seen from the presented piezogram, the piezogram
II, characterizing the oil-saturated part of the reservoir
of the western part of the area, is common for both
areas. It follows that the oil-saturated parts of the
western (reefless) and eastern (reef) areas are
communicated with each other and have a single VOC
at minus 3388 m, while their gas-condensate parts are
separated and have different VOC marks, which fully
agrees with the refined geological model of the field.
To build an epiure of the gas-condensate part of the
eastern reservoir, there are not enough pressure
measurements at different elevations of the latter: as
of the date of reserve calculation, there is only one
pressure measurement made near well №.4, the value
of which\ underestimated by 1.3 kg. In this regard, the
epiure III of formation pressures of the gas-saturated
part of the reservoir of the eastern section in view of
the calculated density of gas in formation conditions,
determined by the composition of formation gas of the
eastern dome and equal to 0.25 g/cm
3.
Thus, the piezogram of the productive reservoir made
it possible to solve and justify a number of important
geological tasks:
determine the GOC of the western section; confirm
the VOC of the eastern section;
justify the commonality of VOC for the entire area;
justify the hydrodynamic connection between the
western and eastern sections of the field;
determine the density in formation conditions and
phase state of hydrocarbons;
justify the formation pressure in your part of the
eastern dome.
As noted above, it is impossible to identify fracture-
type reservoirs in the productive formation section and
Volume 04 Issue 02-2022
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VOLUME
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SJIF
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OCLC
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–
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Publisher:
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estimate their parameters according to the available
data. In this regard, only fracture-pore type reservoirs
with a standard porosity of 8% for oil and 6% for gas are
included in the calculation of reserves.
XV-a horizon is the main (within the western part of the
estimated field) by the volume of conditioned
reservoirs, and all of them are oil-saturated. Since they
are located significantly below the GOC and above
VNK, taken respectively at minus 3271 m and 3388 m.
the total effective oil-saturated thickness in the section
of well 1 is equal to 12.4 m.
In the section of well №3, according to logging data,
only three conditioned interlayers with a thickness of
3.2 m in total, accepted based on logging data as oil-
saturated, despite the results of their testing by two
intervals of perforation, which gave weak water
inflows. The absence of chemical analyses of the water
samples, proving that they belong to the formation
water, allows us to assume that during the sampling
process there were inflows of filtrate flushing fluid.
In the sections of the nearest wells (№№ 6-Zafar, 4-
Shakarbulak), which concealed XV-a horizon, one 0,8 m
thick interlay in well 4 and two interlayers of the total
thickness of 2 m in well 6-Zafar were singled out. Taking
this into account, as well as the results of sampling, oil-
bearing capacity contour of the object under
evaluation divided into two fields - eastern and
western - with different category (C1 and C2) and
different values of effective oil-saturated thickness,
which are 12 m and 3 m, respectively.
The oil-bearing contours (external and internal) for the
XV-a horizon are plotted on the structural map of the
horizon roof in accordance with the adopted GOC and
VOC marks up to the intersection with the eastern
boundary of impermeable epigenetic nature, which
limits the western part of the oil deposit.
In terms of typing, the oil deposit of the XV-a horizon,
which is part of a larger massive deposit, should be
qualified as a reservoir of the reservoir-well type,
bounded by a zone of epigenetic mineral formation
(impermeable zone of epigenetic nature), Dimensions
of the deposit: length - 4 km; width - 3.5; height - 94 m.
The next (intermediate in the section) counting object
is XV-PR horizon, in which reservoirs fracture-pore type
are distinguished only in the sections of wells 1 and 6-
Shakarbulak in the sections of the nearest wells (3-
Zafar, 4-Shakarbulak) located beyond the contour of
oil bearing on this object, they are absent. According to
available data, it is impossible to establish the nature of
their distribution over the area, especially within the
contour of oil-bearing capacity. In this connection a
small counting field around the well No.1, conditionally
limited by a semicircle of radius 0.9 km, equal to half of
the distance between the wells 1 and 3, and the line of
the inner oil-bearing area contour of the given object
was singled out.
Within the counting field, the productive part of the
XV-PR horizon divided into two strata separated by a
12-meter interval of dense limestones. According to the
adopted GOC at the level of minus 3271 m in the
western part of the counting field the reservoirs of the
upper member are gas-saturated. At the same time,
the effective gas-saturated thickness is m within the
inner gas-bearing contour of the upper member.
In the eastern part of the selected counting field,
limited by the outer contour of gas content of the
Volume 04 Issue 02-2022
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VOLUME
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SJIF
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)
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IF
–
7.856
Publisher:
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upper pack, both packs are oil-saturated. The area
bounded by the outer and inner gas-bearing contours
is a zone of two-phase saturation (gas and oil) in the
upper member.
Considering this, the calculated field divided into two
parts at the isotypes of minus 3260 m, corresponding
to the middle line between the outer and inner
contours of gas content, which allows calculating
reserves according to a simplified scheme - without
drawing maps of the effective thicknesses, with the
allocation of three parts:
1)
Gas-bearing, for which the total effective thickness
of the upper stratum equal to 7.6 m is assumed,
taking into account the lower porosity limit of 6%
for gas-bearing reservoirs;
2)
Under gas oil-saturated, for which the effective oil-
saturated thickness of the lower pack of XV-PR
horizon assumed 2.2
3)
Eastern oil-saturated - with a total effective oil-
saturated thickness equal to 7.8 m, taking into
account conditioned reservoirs throughout the
section of XV-PR horizon.
In the XV-DERF horizon, only 1 pore-type reservoir, 0.8-
1.2 m thick and 0.1 open porosity coefficient, lies
directly under the lower anhydrites of the Kimmeridge
titon and distributed throughout the western part of
the evaluated field, as well as in the adjacent areas.
The contours of gas and oil-bearing area drawn,
respectively, at isohypses minus 3271 and 3388 m
(according to the adopted levels of GOC and VNK) to
their intersection with the boundary of the
impermeable zone, which is limited to the deposit from
the sides.
Dimensions in the accepted boundaries:
Of the deposit as a whole: length - 5.5 km;
maximum width - 4.5 km; height - 153 m.
Oil-saturated part: length - 6 km along the isohypse
minus 3320 m; width - 0.8 to 2.3 km; height - 117 m.
The gas cap characterized by a dome-shaped
contour measuring 3.2 x 3 km and with a height of
36.
The deposit of this counting object by type is
stratum-volumetric, limited by impermeable zone.
Considering the degree of exploration, calculated
reserves distributed as follows:
C1 category includes:
Oil reserves XV-a horizon of the eastern part of the
deposit and XV-PR horizon;
Reserves of gas and associated components of the
XV-DERF horizon.
Category C
2
includes:
Oil reserves of XV-a horizon of the western part of
the deposit and XV-DERF;
Reserves of gas and associated components of the
XV-PR horizon.
Exploration well №4, drilled in 1989, was the pioneer of
the eastern, reef section of the estimated field.
Moreover, tested in the production string in 1990. This
is the first well in the area that opened the reef type of
section. According to the refined geological model, the
well opened the outer slope of the reef structure,
characterized by a reduced thickness of the XV-P
horizon, represented by reservoirs with high reservoir
properties. With a porosity of up to 20% and a
permeability of up to 536 mln (according to laboratory
studies of a core taken from this interval with 100% -
takeaway). At the same time, rather modest inflows
obtained in all test modes, which clearly do not
correspond to the FES of the enclosing collectors. The
calculated value of permeability, determined from the
test data of the interval 3765-3760 m and equal to 39
mln, turned out to be half an order of magnitude less
than according to the study of the core taken from this
interval with 100% recovery. Which is direct evidence of
the natural permeability of reservoirs by penetration
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into drilling into the pore space of clay particles and
fluid filtrate.
The negative impact of the penetration of the filtrate
and solid components of the flushing fluid maximally
manifested in reservoirs with deterioration in the
reservoir properties and with a predominantly
fractured permeability. This is what makes it possible
to obtain non-industrial inflows from the top part of
the XV-P and the bottom part of the XV-DERF, opened
by well №4 above the WOC mark and represented,
apparently, by fractured reservoirs, and the overflows
from highly porous gas-saturated reservoirs when
testing the lower, oil-saturated part of the XV- P
horizon.
Taking into account the drilling conditions, one should
also consider the results of testing well № 5, which
revealed a thin-layered section of the XV-HP horizon
with a low reservoir quality of pore-type reservoirs and
massive high-capacity reservoirs of the XV-P horizon in
a solution with a density of 1.34 g/cm
3
; with pressure on
the layers of 106-115 kg/cm
2
. At the same time, because
of testing the XV-P horizon, formation water inflows
with a flow rate of m
3
/day were obtained and from the
intervals of the XV-HP horizon located above the mark,
weak, non-commercial inflows of oil and water were
obtained.
Well №7 opened a similar section (XV-HP, XV-P
horizons), but only higher in elevation. GOC in this well
opened in the uppermost XV-HP, and OWC 12 m below
the roof of the XV-P horizon. The productive part of the
section was not covered by testing, due to the collapse
of the production string after testing a number of
objects in the water-saturated part of the XV-P horizon,
which gave formation water inflows with a flow rate of
up to 108 m
3
/day. Field studies of OIPK, carried out in
the process of drilling a well, obtained direct
confirmation of the oil saturation of the upper part of
the XV-P horizon - from a depth of 2832 m, which is 9 m
higher than the accepted WOC, oil was obtained in the
amount of 12 liters.
Well № 9 was drilled in the oil saturation zone of the
XV-HP horizon, on a light mud with a density of 0.9
g/cm
3
, with a flow rate of 194 m/day through a 114 mm
drilling tool. Based on GIS data, the WOC was
determined at the level of minus 3388 m (depth 3834
m), in the lower part of the XV-HP horizon. However, in
the process of testing two oil-saturated intervals in the
middle and upper parts of the XV-HP horizon of which
the first (3817-3810 m) is characterized by high
reservoir properties (porosity - 12-19%. Permeability - 27-
688 mln, according to laboratory studies of the
presented of the core material taken from the
perforation interval), weak oil inflows obtained which
clearly contradicts the data of the study of a large
number of core samples, IPG and well logging. In this
case, the negative influence of drilling in technology
and, possibly, well casing is so obvious that there is no
need to bring in any additional reasons to explain the
results of testing. In addition, this despite the fact that
the well was drilled with relatively small repressions.
Well №12 drilled on the northern, high-elevation
tectonic block, outside the estimated area according to
the updated geological model. The well opened a full
section of the XV-HP, XV-P horizons and, partially, the
XV-PR horizon.
When testing the lower half of the XV-HP horizon,
improved in terms of reservoir properties, as well as
the upper part of the XV-P horizon, weak water inflows
with minor oil shows (in the form of films) obtained in
the intervals of the XV-HP horizon.
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Publisher:
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The upper part of the XV-HP horizon, in which reservoir
interlayers with degraded properties are widespread,
not sampled as of the date of reserves estimation.
Nevertheless, the oil and gas potential of the dome, in
the arch of the second well drilled, is estimated by us
as low, given its small size and small amplitude, as well
as the low FES of reservoirs that may turn out to be oil
or gas saturated.
Well №13 laid on the recommendation of the
Uzbekgeofizika association, according to the updated
map (S.N. Zuev and S.I. Kalugin) in optimal structural
conditions and within the predicted position of the reef
crest. At the bottom of 3651 m, it liquidated for
technical reasons. Judging by the limited logging data,
the borehole penetrated the top of the lower
Kimmeridgian-Titonian anhydrites at a depth of 3622
taking into account the estimated thickness of the last
26 m (from the beginning of the record, see BK). The
top of the XV-horizon was exposed at a depth of 3648
m (-3219 m), which turned out to be significantly higher
than on the above map.
Well №14 laid according to the definition of the
“Uzbekgeofizika association as a backup well. №13 in
order to clarify the geological structure of the field, the
phase state of HC, OWC and GOC, the selection and
subsequent study of the presented deep oil samples to
determine the volumetric coefficient for calculating
the reserves of the field.
From the above data, it seen that the geological
effectiveness of exploration drilling in the eastern
section of the estimated area is very Low. Of the 6
wells drilled here, commercial inflows were obtained
from only two intervals of the XV-P horizon in well № 4
and one interval of the XV-HP horizon in well № 9 (in an
open hole during PDT). All this makes a negative
impression regarding the industrial value of the
deposit and causes distrust among many specialists,
including foreign experts, in the reserves of
recoverable for 5 million tons. For the eastern section,
accepted on the state balance sheet based on the
materials of the operational calculation of reserves,
performed
by
the
association
“Uzbekneftegazgeologia”. This attitude towards the
estimated field caused by the traditional approach to
the geometrization of reef reservoirs, in which
significant errors made in the estimates of oil and gas
reserves confined to them. In this regard, below is a
brief description of the method used (3).
Characterization of the methodology used and the
results of the geometrization of the reef reservoir in
the eastern section of the field.
The technique of geometrization of reef traps in
Western Uzbekistan developed in 1982 and since then
it has been used and presented in reports on the
calculation. Moreover, recalculation of oil and gas
reserves in many fields (Southern Kemachi, Umid,
Jarchi, Zevardy, Alan, Dengizkul, Shurtan, Kokdumalak,
South Tandyrcha, Dzharkuduk, etc.), so there is no
need to lay it out in detail.
The essence of the methodology is to use a
fundamental sedimentation model common to all reef
structures in the region, according to which they
characterized by:
Flat-topped structure;
Steep outer slopes;
The presence of a narrow ridge in the massive part of
the edifice (XV-P horizon) associated with the outer
slope of the edifice (in single edifices located in the
depression zone, they close and form an annular ridge,
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Publisher:
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and within the barrier reef it can be traced in the form
of a narrow strip along the outer slope);
Compensation of the inner slope of the XV-P horizon
with sedimentary-layered deposits of the XV-HP
horizon, which are deposits of the back-reef lagoon of
the barrier reef and internal lagoons of single
structures;
Thinning of the XV-HP horizon from the rear zone of
the reef towards the outer boundary until it is
completely wedged out on the crest;
Reduced (10-30 m) in the top zone of the reef mass and
sharply increasing on the outer slope to a maximum
value in the conjugated part of the depression zone
with a thickness of overlying important Kimmeridgian-
Titonian anhydrites;
Maximum under the crest and outer slope of the reef,
reduced in the depression zone to 5-10 m and in the
inner zone of the reef until the thickness of the
enclosing sediments of the XV-DERF horizon is
completely wedged out.
Taking into account the above features, a
sedimentation model of the Shakarbulak barrier reef
fragment built in the form of a section, as well as a map
of the total thicknesses of the XV-HP horizon. Which
subsequently used when delivering a structural map of
the limestone roof a hypsometric map of the surface of
the XV-P horizon and a profile section of the productive
strata. The hypsometric map of the surface of the XV-P
horizon compiled by the method of convergence – by
summing up the structural map of the top of the
limestones of the thickness map of the XV-HP horizon.
The use of the sedimentation model of the reef mass
made it possible for the first time to perform a
separated geometrization for the estimated field and,
on this basis. Calculate oil and gas reserves
differentially for the XV-P and XV-HP horizons, despite
the absence of wells that opened the reef crest zone,
which led to a radical reassessment of the potential oil
and gas potential of the eastern section of the field due
to the XV-P horizon. Which almost completely
represented by cavernous-porous rocks with high
reservoir properties.
Taking into account the established levels of water-oil
contact (-3388 m) and GOC (-3327 m), the contours of
oil and gas potential were determined, which were
drawn along the corresponding isohypses on maps of
the limestone roof and the surface of the XV-P horizon.
The oil and gas condensate deposit of the eastern
section, confined to the reef complex (XV-P+XV-HP
horizons), belongs to the massive type. The size of the
oil part of the deposit - in general for the eastern
section: by - 8.2 km; width - 3.0 km; height -61m;
Along the XV-P horizon:
Length - 8.2 km; width - 1.52 km; height - 61 m.
XV-HP horizon:
Length - 7.8 km; width - 2.2 km; height - 61 m.
Gas cap dimensions:
In general for the eastern section: length - 5.8 km;
width - up to 2 km; height 08 m.
Along the XV-P horizon:
Length - 5.8 km; width - up to 1.2 km; height - 107 m;
XV-HP horizon:
Length - 5.7 km; width - up to 1.7 km; height.
The need to separate the XV-P and XV-HP horizons into
independent countable objects is due to the
completely different character of the structure and
distribution over the area of both total and effective
thicknesses.
The effective oil-saturated thickness of the XV-P
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Publisher:
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horizon is practically the total thickness of the oil-
saturated interval and is 60 m in the case of the gas-
bearing contour for this horizon, which is also the
internal oil-bearing contour. Outside this contour, the
average oil-saturated thickness is 30 m.
The maximum effective gas-saturated thickness of the
XV-P horizon in the apical part of the gas cap is 100 m
the weighted average thickness within the gas-bearing
contour is 43 m.
Along the XV-HP horizon, a zone of increased oil-
saturated thicknesses with a maximum value of up to
13.6 m form a narrow strip, the axial line of which
almost coincides with the line of the outer contour of
the gas content, and in some places the line of the
inner contour of the oil content. Within this strip, the
effective oil-saturated thickness ranges from 4 to 13.6
m, and the weighted average value is 8.5 m.
More than half of the entire oil-bearing area of the XV-
HP horizon occupied by an annular zone bounded by 4-
meter and zero isopachs. Taking into account the
difficulties of extracting oil reserves of this zone,
confined to low-permeable reservoirs, the contour for
calculating oil reserves along the XV-HP horizon taken
according to a 2-meter isopod of effective oil-saturated
thicknesses.
The nature of the distribution of the effective
thicknesses of the XV-HP horizon controlled by the line
of the internal gas-bearing contour of the given
horizon (it is also the gas-bearing contour of the XV-P
horizon). In addition, is in good agreement with the
geological model – on both sides of this line, the total
thickness of the gas-saturated interval of the section
XV-HP horizon is reduced to zero. The maximum
effective gas-saturated thickness is determined
somewhat to the south of well №7 and is 10 m by
analogy with the sections of wells №.7 and 9 and taking
into account the total thickness of the XV-HP horizon in
this place. With a wound of 40 m according to the total
effective gas-saturated thickness according to sections
of these wells is 11 m, taking into account the boundary
value of porosity for a gas-saturated reservoir of 6%.
Based on the research conducted, the following
conclusions and recommendations drawn:
1.
Drilling of priority project wells carried out in the
XV-P area of the horizon. The proposed
development zone of the XV-P horizon is located in
the area limited by wells № 2,9,7,5,4. Wells № 14,
20 and drilling № 17 are located in this zone. The
need for priority drilling of the zone of distribution
of the XV-P horizon explained by the fact that more
than 80% of recoverable oil and gas reserves are
concentrated on this horizon.
2.
The coefficients of productivity, hydraulic
conductivity and permeability of the formations
determined by the results of well research vary
according to the results in a very wide range. This
is because in exploratory wells, horizons XV-P, XVa,
XV-PR and XV-DERF, which differ sharply in their
filtration-capacitive properties, were tested.
3.
Comparison of the porosity properties of the
horizons determined by the methods of steady
production and pressure recovery shows that in all
the studied intervals, the reservoir properties of
the remote part of the formation are higher than in
the bottom whole zones. In this regard, when
inducing inflow from the reservoir, it is necessary
to carry out methods of intensifying oil production.
4.
The results of calculations of lateral rock pressure
show that the decrease in well productivity at large
drawdowns does not occur due to the closure of
fluid-conducting fractures. Most likely, with an
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increase in drawdown, the oil-containing pores of
the rocks do not completely feed the main
filtration channels (fractures).
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