A.I. Krikunov, A.Ye. Ryzhov, L.A. Filippova, N.Yu ...

74 Issue 2: 2015 collection

English-language digest

Keywords:

well, field,

sedimentation, wash-out,

horizon, correlation,

reference point.

UDC 551.7:551.24 (470+571)

A.I. Krikunov, A.Ye. Ryzhov, L.A. Filippova, N.Yu. Kanunnikova

Determination of location for Botuoba productive horizon and KhM1, KhM2 strata of Khamaki productive horizon in the southern part of the Chayanda oil-gas-condensate field

The southern periphery of the Chayanda oil-and-gas-condensate fi eld (OGCF) is described by a very complex structure of the early Vendian terrigenous deposits and absolutely insuffi cient level of their study. Before 2000, when the last estimation of the oil, gas and associated components reserves was conducted for all the productive horizons of the fi eld, 5 wells were drilled here: 274-01, 752, 803, 806 and 808. Later, wells 321-52, 321-53, 321-54, 321-55, 321-57, 321-71, 321-74 were drilled in 2009–2012; wells 321-51, 321-56, 321-69, 321-70, 321-73 and 321-76 in 2013; and wells 321-58, 321-68 and 321-75 in 2014. During the same year, 3D seismic operations were conducted in this territory and structure maps were built for a number of seismic level refl ectors occurring in Cambrian and Vendian rocks. Besides others, graphical constructions were derived by the bottom of Upper Byuk carbonate rocks covering Botuoba oil and gas bearing sandstones over much of the fi eld area; and by the bottom of the Khamaki productive horizon. An analysis of the resulting materials demonstrated that the positions of fault lines on all these maps does not depend on the deposit age and always remains constant; which can lead one to a conclusion that only young faults that formed after Vendian terrigenous carbonate complex formation, or those which repeatedly demonstrated activity are plotted on the maps. The question is still open whether intraformational or buried faults exist in Precambrian deposits, which might be formed during signifi cant structural transformation periods, when deposits of various ages were brought to the surface, eroded, or buried deeper under the impact of tectonic forces. It is quite diffi cult to assume that there were no structural transformations related to disjunctive tectonics during the Vendian period, which covers a time interval of 80 million years. The very complex geological structure of the southern part of the Chayanda fi eld and clearly insuffi cient level of its study are demonstrated by the contour map prepared by overlaying structure maps built at different times and by different authors (fi g. 1).

The southern end of the Chayanda fi eld, besides potentially being used to increase the area of gas and oil deposits, also draws attention by the fact that an underground helium concentrate storage is planned in the area of well 808. In this context, also interesting is the fact that the columns of the wells drilled here are dissected and compared differently by different authors. Thus, fi g. 2 shows the currently adopted correlation diagram for the line of wells 321-56, 321-58 and 321-75. All the known productive horizons of the Chayanda fi eld have been isolated in these wells. The Botuoba subformation and strata KhM1 and KhM2 of the Khamaki productive horizon have been isolated in all the three wells. The correlation diagram shows that the carbonate deposits of the Byuk formation, successively and without any intervals in sedimentation, rest on Botuoba subformation rocks, which, in turn, grade to the bedding claystones. Down the column, these claystones are replaced by the KhM1 stratum deposits, which rest erosively on claystones covering the productive horizons of the KhM2 stratum rocks. The sandstones, gravelites, and siltstones of the KhM2 stratum rest successively on the bedding shaled-out rocks of the Lower Parshinskaya subformation and then replaced by Talakh productive horizon rocks.

It is diffi cult to agree with such a dissection and well column correlation. The earlier published work [1] clearly demonstrates that the carbonate deposits of the Byuk formation rest on the bedding rocks with deep erosion. Due to this circumstance, there are no

75Proceedings of Gas Industry Research and Development

Vesti Gazovoy Nauki scientific and technical collected book

productive Botuoba sandstones in the southern part of the Chayanda fi eld. Also, there are no such sandstones in the south-eastern periphery of the fi eld, designated as Samanchakit block in the structural maps prepared in 1999 and 2012. An indirect proof of this is that not only gas or oil infl ows were obtained, but even no reservoir rocks were found under the carbonaceous deposits of the Byuk formation in any of the sixteen wells drilled here until now. Besides that, it is doubtful that some researchers found the KhM1 stratum of the Khamaki productive horizon in the columns of wells 321-56, 321-58 and 321-75 for a good reason. It should be added that a number of intraformational erosion surfaces can be identifi ed in the roof part of and inside of the KhM2 stratum. It is possible that there is also a sedimentation interval existing on the boundary between the Talakh and Parshinskaya formations [2–4].

The matter of the presence or absence of the Botuoba subformation and the KhM1 stratum of the Khamaki productive horizon in the interval of rocks covering the KhM2 stratum is considered suffi ciently important. This matter determines the quality of the cover for the underground helium storage planned for construction in the KhM2 stratum. The presence of reservoir rocks in this interval of deposits can seriously

degrade the insulating properties of the assumed impermeable layer.

To prove the above considerations and to ascertain the internal structure of the early Vendian terrigenous rock complex commonly found in the southern part of the Chayanda fi eld, Gazprom VNIIGAZ LLC engineers prepared a correlation diagram1 along the line of wells 321-56 – 321-58 – 321-75 (fi g. 3). Large amount of core was taken for all the three wells, which allows to determine the petrographic, lithological, and petrophysical properties of the reservoir rocks and impermeable layers with a good degree of certainty. However, it should be noted that, since wells 321-58 and 321-75 were only drilled in 2014, their detailed studies are not complete yet, and only the results of operational studies can be used today.

The Botuoba subformation can be identifi ed in the 1508–1514.7 m interval in well 321-56 in fi g. 2. This subformation, or the Botuoba

1 For more detailed, reworked version of the diagram, see fi gure 2 in the article Krikunov A.I. Results of cyclostratigraphic analysis aimed at refi ning the history of the terrigenous Vendian deposits forming at the southern periphery of the Chayanda oil-gas-condensate fi eld / A.I. Krikunov, A.Ye. Ryzhov, L.A. Filippova et al. // Vesti Gazovoy Nauki: Actual issues in research of stratal hydrocarbons systems. – Moscow: Gazprom VNIIGAZ LLC, 2015. – No. 4 (24). – P. 128.

Fig. 1. Contour map of southern part of Chayanda fi eld

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stratigraphic prospecting exploratory

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Fig. 2. Correlation diagram of Chayanda fi eld along line of wells 321-56 – 321-58 – 321-75: GK – gamma-ray logging; NGK – neutron gamma-ray logging (OOO “The Center of Scientifi c Research,

Design, Fossil Raw Materials Geology”, or OOO “CNIP GIS” for short, 2014)

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productive horizon, is represented in the prevailing part of the Chayanda fi eld, as a rule, by quartz sandstones and siltstones. However, according to the core description by Gazprom VNIIGAZ LLC, the following rocks are found at the respective depths in well 321-562:

• 1511.00–1511.56 m (1507.80–1508.36 m) – gray and light gray anhydrite. Structures: clouded, patchy;

• 1511.56–1513.61 m (1508.36–1510.41 m) – yellowish gray dolomite with light gray anhydrite lenses and interlayers. Structures: stromatolithic, veiny, lenticular;

2 Here and hereinafter in well descriptions depths ascertained to establish correlation between the core and the infi eld logging data are provided in parentheses.

• 1513.61–1514.00 m (1510.41–1510.80 m) – mixed terrigenous carbonate rock, anhydritic sandy dolomite. Yellowish gray, gray. Structures: fi ne parallel horizontal layered, low-inclined;

• 1514.00–1516.10 m (1510.80–1512.90 m) – dolomite with frequent claystone interlayers. Yello-wish gray, dark gray, almost black color. Structures: sliding, fi ne parallel horizontal layered, low-inclined;

• 1516.10–1517.57 m (1512.90–1514.37 m) – bedding of dark gray, almost black claystone and yellowish gray dolomite. Structures: layered, interrupted layered, roiling, non-uniform undulating. Dolomite straticules are broken, forming intraclasts of light gray fi nely crystalline anhydrite. Large caverns (up to 3 cm) fi lled with salt are found in dolomite interlayers;

Fig. 3. Correlation diagram of Chayanda fi eld along line of wells 321-56 – 321-58 – 321-75 (Gazprom VNIIGAZ LLC, 2014)

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• 1517.57–1525.00 m (1514.37–1521.80 m) – dark gray, almost black, greenish gray claystone. Structure: fi ne parallel horizontal layered. Large pyrite crystals (up to 2 cm) are found. The rock is actively broken by fractures into plates with a thickness of 1–3 cm.

The brief core macrodescription provided indicates that the entire deposit interval in question, identifi ed by some researchers as the Botuoba subformation, is mostly represented by carbonates and sulfates more typical for the Upper Byuk subformation than for the Botuoba productive horizon. Fragments of fi nely crystalline anhydrite are found at the bottom of the interval, between dolomite and claystone interlayers. The presence of these fragments indicates a probable depositional break. Also found here are caverns fi lled with salt, the occurrence of which at the Chayanda fi eld is fairly frequently associated with erosion surfaces.

In well 321-58, core on the boundary of Byuk carbonates and early Vendian terrigenous deposits was not sampled.

At the correlation diagram by OOO “CNIP GIS” (see fi g. 2), the Botuoba subformation in well 321-75 was identifi ed in a depth interval of 1539.5–1548.5 m. According to the operational core description made at the well, the rock interval where core was sampled from is predominantly represented by carbonaceous deposits (core in this well was sampled3 starting from 1544 m):

• 1544.00–1544.58 m (1542.45–1543.03 m) – dolomite with inclusion of psammitic size terrigenous material. The upper 28 cm are occupied by gray dolomite with interlayers (1–2 mm) of dark gray clayey, rarely brownish gray dolomite. Below that, the color changes to brownish gray. Rare nodules (1–3 mm) of white anhydrite are found throughout the stratum. The upper 5 cm of the stratum are represented by white anhydrite; a small layer (2–5 mm) of gray claystone is identifi ed near the bottom; white anhydrite (5–8 cm) rests below that;

• 1544.58–1545.05 m (1543.03–1543.50 m) – gray brown cryptocrystalline dolomite with non-uniform white anhydrite nodules (1–3 mm to 1–2 cm);

• 1545.05–1546.25 m (1543.50–1544.70 m) – gray, brownish gray dolomite with non-uniform white anhydrite nodules 2 mm to 2 cm in size.

3 To correlate with logging data, core should be raised by 1.55 m.

The dolomite is undulating layered in some areas (1.15–1.23 m from the spudding drilling beginning), with a straticule angle of 10–20°. Greenish gray claystone is found at a depth of 1.46–1.62 m, a thin layer (1–2 cm) of sandy gray brown dolomite under it, a claystone interlayer within an interval of 2.1–2.16 m from the spudding drilling beginning, and large inclusions (2–7 cm) of white anhydrite at the contact with the underlying stratum;

• 1546.25–1547.70 m (1544.70–1546.15 m) – laminated gray, light gray, brown dolomite. The lamination is predominantly horizontal, undu-lating and oblique (angle 0–30°) in some areas. Round-shaped silifi cations (0.5–2 cm) are found. An interlayer of gray claystones is found within an interval of 3.45–3.55 m from the spudding drilling beginning. At the stratum top (the fi rst 3–5 cm), lamination is broken by anhydrite inclusions;

• 1547.70–1548.05 m (1546.15–1546.50 m) – gray dolomite with multiple thin short wavy fractures without any visible mineral matrix;

• 1548.05–1548.38 m (1546.50–1546.83 m) – brownish gray dolomite with inclusion of psammitic size terrigenous material. At the stratum top, interlayered with gray claystones;

• 1548.38–1549.13 m (1546.83–1547.58 m) – gray, brownish gray cryptocrystalline, intermittently laminated dolomite;

• 1549.13–1550.00 m (1547.58–1548.45 m) – greenish gray sandy dolomite.

Massive greenish gray Parshinskaya formation claystones rest below the carbonate deposits mentioned above.

The above core description indicates that it is probably incorrect to classify the rock interval at depths of 1539.5–1548.5 m in well 321–75 as the Botuoba productive horizon.

Consider next the description of core from the wells drilled nearby and surrounding the wells included in the correlation diagrams (see fi g. 2 and 3). For more convenient data representation, Gazprom VNIIGAZ LLC prepared three more detailed correlation diagrams II–II (fi g. 4), III–III (fi g. 5) and IV–IV (fi g. 6), which cross the line of wells 321-56, 321-58 and 321-75 at a nearly right angle and in which 19 synchronous reference horizons are identifi ed.

In wells 274-01, 321-54, 321-74, and 808, core was not sampled at the boundary of carbonate and terrigenous Vendian rocks. In well 803, the roof of the terrigenous early Vendian, according to logging data, is found at a depth of 1440 m. Core in this well was sampled from the rock interval at depths



of 1437.7–1464.7 m, but neither the core nor its description are available any more due to objective reasons. In well 321-57, the terrigenous Vendian rock roof is at a depth of 1429.5 m (see fi g. 4). In a depth interval of 1421–1430 m core was sampled4:

• 1421.00–1422.00 m (1423.00–1424.00 m) – light gray and gray anhydrite. Structure: patchy. The rock is compact, massive, and strong, with

4 To correlate the core sampling depth with logging data, core should be lowered by 2 m.

single claystone interlayers with a maximum thickness of 0.5 cm;

• 1422.00–1423.00 m (1424.00–1425.00 m) – frequent thin bedding of dolomites with anhydrite. Greenish gray, gray, yellowish gray rocks;

• 1423.00–1424.00 m (1425.00–1426.00 m) – yellowish gray and gray dolomite with anhydrite. Structures: veiny, layered. Thin dolomite interlayers interrupted by anhydrite. Single claystone interlayers with a maximum thickness of 5 cm are found;

Fig. 4. Chayanda fi eld: correlation diagram along line of wells 321-54 – 321-75 – 321-57

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synchronous reference horizon

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• 1424.00–1425.37 m (1426.00–1427.37 m) – dolomite with anhydrite. (There is little anhydrite). Anhydrite inclusions virtually do not interrupt fi ne parallel lamination. The rock is yellowish gray, intermittently gray. Structures: layered, laminated, veiny, lenticular due to single anhydrite lenses with maximum dimensions of 5 cm;

• 1425.37–1426.00 m (1427.37–1428.00 m) – massive dense layered, laminated dolomite. The rock is yellowish gray;

• 1426.00–1428.11 m (1428.00–1430.11 m) – yellowish gray dolomite, gray and greenish gray claystone. Dolomite prevails. Claystone sometimes contains dolomite and terrigenous fragments. The thickness of claystone interlayers reaches 10 cm;

• 1428.11–1430.00 m (1430.11–1432.00 m) – greenish gray claystones with rare interlayers of gray and greenish gray siltstones. In the top part, claystones contain terrigenous fragments with maximum dimensions of 1 mm. Crushing zone.

Fig. 5. Chayanda fi eld: correlation diagram along line of wells 321-74 – 321-58 – 808

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Fig. 6. Chayanda fi eld: correlation diagram along line of wells 803 – 321-56 – 274-1

Large number of gliding planes. The rock is heavily fractured.

All the above gives ground not to show the Botuoba horizon or Botuoba subformation in the terrigenous Vendian roof in wells 321-56, 321-58, and 321-75 at the correlation diagram (see fi g. 3). We believe that productive Botuoba sandstones in this area of the Chayanda fi eld are completely eroded and Byuk formation carbonate deposits rest erosively on the bedding rocks. This conclusion is proven by negative results of drill stem testing conducted in well 321-56 at a depth of 1502–1525 m and the absence of reservoir rocks in wells

321-58 and 321-75 in the rock interval under the Upper Byuk subformation carbonaceous deposits (according to logging data).

The top stratum of the Khamaki productive horizon (KhM1) is identifi ed below the Botuoba subformation bottom (14–18 m) at the correlation diagram of CNIP GIS (see fi g. 2). At the Chayanda fi eld, its thickness, as a rule, is approximately 4–8 m. Lithologically, this stratum is normally represented by coarse-grained sandstones, gravelites, less frequently by conglomerates or breccia. A regional erosion surface, which is found practically throughout the entire territory of

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P22

P28

P27

P26

P25

P24

P23

P15

P14

P13

P12

T1

T2

KhM 12

KhM 22

KhM 32

KhM 42

KhM 12

KhM 22

KhM 32

KhM 42

Well 321-56 Well 274-01

1530

1540

1550

1560

1570

1580

1590

1430

1440

1450

1460

1470

1480

1490

1600

1610

1620

1500

1510

1520

1630

1640

1650

1530

1540

1550

1560

1570

1580

1590

1490

1600

1610

1620

1500

1510

1520

1630

1640

1650

1660

1670

1510

1520

1530

1540

1550

1560

1570

1580

1590

1600

1610

1620

1630

1640

1650

1660

1670

1680

1690

1700

1710

1720

1730

1522

1531

1P1

Legend:


erosion surface


BYUKCARBONATES

BYUKCARBONATES

Subf

or-

mat

ion

Subh

ori-

zon

Form

atio

n

Syst

em

Hor

izon

Dep

th, m

Dep

th, m

Dep

th, m

Cyc

lite

BYUK

TIR

SKY

Subf

or-

mat

ion

Subh

ori-

zon

Form

atio

n

Syst

em

Hor

izon

Cyc

lite

BYUK

TIR

SKY

TALA

KH

TALA

KH

KH

AM

AK

I

2

KH

AM

AK

I

2

LO

WE

R

LO

WE

R

VE

ND

IA

N

VE

ND

IA

N

NE

PS

KY

NE

PS

KY

PA

RS

HI

NS

KA

YA

PA

RS

HI

NS

KA

YA

MI

DD

LE

MI

DD

LE



the Chayanda fi eld, is located at the base of the KhM1 stratum. It should be noted that, according to logging data, reservoir rocks are not identifi ed in any of the three wells in the depth interval marked as the productive stratum KhM1 at the correlation diagram of CNIP GIS. In well 321-56, core was not sampled where the KhМ1 stratum is marked. In wells 321-58 and 321-75, according to the preliminary core description prepared at core sampling locations, rocks are represented by dolomites with thin claystone interlayers. Concerning nearby wells 274-01, 321-57, 803, and 808, there are no data on respective rock deposits due to the absence of core. In well 321-54, a similar rock interval is identifi ed at a depth of 1634–1637 m (see fi g. 4). Core description is provided further. To correlate core with logging data, core should be raised by 0.8 m:

• 1615.30–1635.30 m (1614.5–1634.5 m) – dark gray, almost black, claystone with rare gray siltstone interlayers. Structures: thin parallel horizontal laminated, striated, lenticular, indistinctly layered. The core is actively fractured with the bedding;

• 1635.30–1637.30 m (1634.5–1636.5 m) – gray, dark gray, almost black silty claystone. Structures: thin parallel horizontal laminated with the elements of graded layering, squeezing and sediment subsidence. The rocks are heavily fractured with the bedding;

• 1637.30–1645.99 m (1636.5–1645.19 m) – dark gray, almost black, claystone with rare gray siltstone interlayers. Structures: thin parallel horizontal laminated, striated, lenticular, indistinctly layered. The core is actively fractured with the bedding.

• In well 321-74, the respective rock interval, according to logging data, is at a depth of5 1542-1546 m (see fi g. 6):

• 1527.34–1540.32 m (1529.64–1542.62 m) – dark gray, almost black claystone. Structures: indistinctly layered, interrupted layered. The core is fractured into individual plates;

• 1540.32–1543.20 m (1542.62–1545.50 m) – greenish gray, gray claystone. Thin parallel horizontal laminated, lightly oblique laminated, lightly roiled. The bottom part in an interval of 1543.00–1543.20 m contains an interlayer of medium-grain and fi ne-grain yellowish gray

5 To correlate the core description with fi eld logging data, the core should be lowered by 2.3 m.

sandstone (mud stream traces). Fractures occur with the bedding;

• 1543.20–1547.00 m (1545.5–1549.30 m) – dark gray, almost black, claystone with gray siltstone interlayers. Structures: fi ne parallel horizontal layered, lenticular; Fractures occur with the bedding.

In all the wells in question, no rudaceous rocks were found in the respective deposit interval.

If a surface of a large regional erosion is present at the base of the productive stratum KhM1, as it is specifi ed at the correlation diagram of CNIP GIS (see fi g. 2), it is unclear what is eroded in wells 321-58 and 321-75, located at a distance of approximately 7 km from each other. In both wells, a dense streak can be clearly seen in well logs exactly 11 m below the assumed erosion surface. This streak can be used as a synchronous reference horizon for well column comparison purposes. The thickness of this streak is approximately 4 m, and it is gradually replaced with more clayey deposits in the southern direction, towards well 321-56 (see fi g. 3, 5). If the erosion is actually present, there would be no 11 m thick rocks remaining in wells 321-58 and 321-75 above this streak.

It follows from what has been said above that the presence of the productive horizon KhM1 and a regional erosion surface at its bottom marked at the correlation diagram of CNIP GIS (see fi g. 2) is rather doubtful. One should agree, though, with the spatial location of the roof and bottom of the productive horizon KhM2. Only the top boundary of the stratum in well 321-58 seems suspicious. We believe that it is unreasonably high and, thus, a sandy streak with a total Power capacity of approximately 6 m is added to the stratum KhM2 (see fi g. 3).

All the above examples positively indicate that neither the Botuoba subformation nor the stratum KhM1 of the Khamaki productive horizon are present in the columns of wells 321-56, 321-58, 321-75. The absence of potential reservoir strata in the sequence covering the stratum KhM2, according to logging data and core macro description, indicates that this sequence can be confi dently considered as an impermeable cover for an underground helium storage.



References1. Ryzhov A.Ye. Boundary position’s update between

lower byukskaya and upper byukskaya subsuit of Chayanda oil gas condensate fi eld with the involvement of the lithological, geological and geophysical criteria / A.Ye. Ryzhov, A.I. Krikunov, L.A. Ryzhova et al. // Vesti gazovoy nauki: Actual problems of studies of hydrocarbon fi eld bedded systems. – Moscow: Gazprom VNIIGAZ, 2013. – V. 1 (12). – P. 161–173.

2. Ryzhov A.Ye. Impact of the internal structure of the Khamakinsky producing horizon and location of its stratigtaphic borders in the southern part of the Chayanda fi eld / A.Ye. Ryzhov, A.I. Krikunov, L.A. Filippova (Ryzhova) et al. // Vesti gazovoy nauki: Actual problems of research of stratal hydrocarbon systems. – Moscow: Gazprom VNIIGAZ, 2014. – № 2 (18). – P. 12–18.

3. Ryzhov A.Ye. Specifi cation of the history of formation of the southern and the Samanchakitsky blocks identifi ed at the Chayanda fi eld during the Pre-Cambrian age / A.Ye. Ryzhov, A.I. Krikunov, L.A. Filippova (Ryzhova) et al. // Vesti gazovoy nauki: Actual problems of research of stratal hydrocarbon systems. – Moscow: Gazprom VNIIGAZ, 2014. – № 2 (18). – P. 19–26.

4. Ryzhov A.Ye. Determination of the degree of infl uence of the tectonic factor on the formation of deposits of hydrocarbons on the Samanchakitsky block of the Chayanda oil and gas condensate fi eld / A.Ye. Ryzhov, A.I. Krikunov, L.A. Filippova (Ryzhova) et al. // Vesti gazovoy nauki: Resource support problems of Russian oil-producing regions. – Moscow: Gazprom VNIIGAZ, 2014. – № 3 (19). – P. 99–105.

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