Architecture and quantitative assessment of channeled clastic deposits, Shihezi sandstone (Lower Permian), Ordos Basin, China Q2 Q1 Available online at www sciencedirect com + MODEL JNGGS52 proof ■ 2[.]
Trang 1Original research paper
Architecture and quantitative assessment of channeled clastic deposits,
Shihezi sandstone (Lower Permian), Ordos Basin, China Q2
Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China
Received 7 September 2016; revised 16 December 2016
Available online ▪ ▪ ▪
Abstract
Lower Permian Shihezi sandstone in Ordos Basin is the largest gas reservoir in China Architecture elements of channel, overbank and floodplain facies of braided channel deposits were identified through an outcrops survey, and their proportion of channel facies have been quantitatively estimated from well logging Characteristics of architecture elements, such as sand thickness, bounding surfaces and lithofacies were investigated through outcrops and core Petrology of Shihezi sandstone has also been studied in detail Analysis on sandstone components shows that monocrystalline quartz with approximately 76% bulk volume, and lithic up to 5%e45% bulk volume, are the two main components Litharenite and lithic quartz sandstone are the main rock types Compaction is concluded by former researchers as the control factor of low permeability Examination through thin section reveals that secondary pores developed well in coarse sand Inter-granular dissolution is included
as the positive effect to increasing porosity, and is concluded as the control factor to the generation of net pay Scale of coarse grained channel fills and channel bar sandstone bodies are quantitatively estimated Strike-oriented, dip-oriented, and vertical distribution of channel fills and channel bar sandstone bodies have been investigated The geometry of sand bodies can be depicted as an elongated lens Subsurface mapping reveals that channel sandstone bodies distribute widely from both lateral and longitudinal cross section profiles, and are poorly connected
Copyright© 2017, Lanzhou Literature and Information Center, Chinese Academy of Sciences AND Langfang Branch of Research Institute of Petroleum Exploration and Development, PetroChina Publishing services by Elsevier B.V on behalf of KeAi Communications Co Ltd This is
an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Keywords: Shihezi sandstone; Lower Permian; Ordos Basin; Architecture elements; Petrology; Quantitative assessment
1 Introduction
Modern fluvial sedimentology had its beginnings during the
World War II, with the work of H N Fisk [1] and his
col-leagues on the depositional framework of the Mississippi
River [2] Researches began on architecture of channeled
reservoir in 1980s [3] and facies analysis techniques for the
detailed description and interpretation of channel-fill
archi-tecture have been improved [4] Over the past 20 years,
outcrop analogs have also been integrated in reservoir
char-acterization and reservoir modeling to reduce uncertainties
and to understand heterogeneities of deposition units in three dimensions [5e7] Geological characterization including ele-ments, pattern and deposition mechanisms derived from out-crops have been proved to be valuable information which can
be used as conditioning data in the recognition and description
of subsurface fluvial architecture[5,8] Ephemeral-fluvial braided systems constitute one of the main reservoirs in many oil and gas fields around the world
[8e13] Reservoir architecture elements and its characteristics are control factors in accumulation and recovery of hydro-carbon[14,15]
The widespread distribution of braided fluvial Shihezi sandstone bodies in the Ordos Basin and their potential as hydrocarbon reservoir warrant a better understanding of the fluvial processes involved in their development Most pub-lished descriptions of the Ordos Basin Shihezi sandstone are
* Corresponding author.
E-mail address: cyjia@petrochina.com.cn (C Jia).
Peer review under responsibility of Editorial office of Journal of Natural Gas
Geoscience.
ScienceDirect
Journal of Natural Gas Geoscience xx (2017) 1 e10
http://www.keaipublishing.com/jnggs
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http://dx.doi.org/10.1016/j.jnggs.2017.01.002
2468-256X/Copyright © 2017, Lanzhou Literature and Information Center, Chinese Academy of Sciences AND Langfang Branch of Research Institute of Petroleum Exploration and Development, Petro-China Publishing services by Elsevier B.V on behalf of KeAi Communications Co Ltd This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).
Trang 2piecemeal and two-dimensional, and are insufficient to
reconstruct adequately their sedimentary architecture as well
as to infer the processes associated with bar formation and
migration, and channel incision and filling Outcrops located
in Liulin County, eastern of Ordos Basin allowed a detailed,
three dimensional description of one Shihezi sandstone body
With more exploration and development wells drilled,
suffi-cient log and experimental data of core analysis makes
reservoir characterization feasible
The purpose of our study is to provide geoscientists and
engineers with qualitative description and quantitative data
from Lower Permian channeled sandstone deposits This data
set is of great importance to success rate of exploration well
and field development strategy
In this paper, we demonstrate a comprehensive approach to
architecture elements analysis integrated with outcrop
inves-tigation and reservoir characteristics of different units
including lithofacies, stratal geometries, and petrophysical
properties derived from laboratory analysis on core samples
2 Data and methods
Braided stream deposits consist of numerous
inter-connected channels, separated by bars[16]and dominated by
coarse-grained sediments such as sands and gravel [17] The
entire channel complex may contain water and the bar may be
submerged during high water period During periods of
drought, only one channel, or even no channel, is active Thus,
multi-cycle sandstone and gravel sheets are deposited in a
braided channel and its width may vary widely with respect to
its thickness With respect to depth, an upper limit of width
can be estimated[18]
By outcrops investigation, qualitative and quantitative data
such as bedform geometry, bedset thickness, and lateral
con-tinuity can be obtained by determining the individual geobody
dimensions of fluvial sandstone and are used to guide the
reservoir characterization [5,19,20] Through Field survey,
thickness of different channel facies can be estimated and
lithofacies can be identified
Complete sets of logs (Latero Log Deep, Latero Log
Shallow, Formation Density Compensated Log, Compensated
Neutron Log, Bore Hole Compensated Sonic Log,
Sponta-neous Potential Log, and Gamma Ray Log) for the reservoir
units were digitized Eletrofacies zonation through well
log-ging extrapolation helps to estimate scale of multi-storey
channels and single-storey channels and log interpretation
can be used to construct cross section maps
Cores obtained from drilling provide direct and detailed
information such as lithology, lithofacies, and sedimentary
structures which are symbols of sedimentary environment and
thin section analysis is the efficient way for pore structure
analysis and pore space characterization
Quantitative data for calculating the proportions of facies
and scale of sandstone bodies were collected by different
spacing well logs from cross section Well logs are commonly
close to actual measured sections[21] Eighty well logs were
used to make the calculations
3 Geological setting and stratigraphy Ordos Basin with area of about 32 104km2is one of the largest sedimentary basins in China Although once wrongly regarded as a relatively stable cratonic sedimentary basin
[22,23], it is now widely considered as a Gondwana-derived fragment of continental crust on the western edge of the North China block [24] Complex tectonic and sedimentary evolutions of the basin have resulted in the formation of various structural units consisting of highly tectonic fold-thrust belts and horst-graben features forming mountainous outer rim of the Ordos Basin (Fig 1) Six first-grade tectonic units can be identified: Weibei Uplift, Yimeng Uplift, Jingxi Flexing Belt, Tianhuan Depression, Western Margin Thrust Belt and Yishaan Slop In contrast, inner part of Ordos Basin shows minor tectonic deformation Microcontinental amal-gamation from Middle to Late Paleozoic provided a broad, gently subsiding craton on which were deposited terrigenous shelf, deltaic and fluvial clastics and associated coals
The regional stratigraphy of the Ordos Basin is illustrated
inFig 2 The basement of the basin comprises Archaean and Lower Proterozoic crystalline rock Middle and Upper Ordo-vician, Silurian, Devonian and Lower Carboniferous units are absent within the major part of the basin According to fission
Fig 1 Simplified geological map of the Ordos Basin and location of the outcrops (Modified from Ref [25] , 2003).
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Trang 3track studies, the basin underwent a regional uplift of almost
2000 m, during which Cretaceous and Palaeogene/Neogene
sediments would have been eroded in most part of the basin
[25] Sedimentary sequence, with thickness of 6000 m in the
center part of the basin, is composed of Lower Paleozoic
marine carbonates, Upper Paleozoic shallow marine to
conti-nental clastic deposits and Cenozoic and Mesozoic conticonti-nental
clastics
The Permian units of the study area are composed of a
braided clastic depositional series which are subdivided into
Shiqianfeng Formation, Upper Shihezi Formation, Lower Shihezi Formation and Shanxi Formation[26] Lower Shihezi
is the main reservoir layer and distributed widely in the basin
It is comprised of numerous narrow and elongate fluvial sandstone bodies that fill channels incised into floodplain strata
4 The hierarchy of depositional units and lithofacies The concept of a hierarchy of depositional scales and the relationship of hierarchy to depositional processes on various time and physical scales was firstly initiated by Allen [27] Miall developed a numerical ranking to the architectural subdivision of fluvial deposits [17] and compared the two classifications[28] In our study, we employ the classification
of Miall[28] 4.1 Bounding surface The most prominent bounding surfaces in the outcrop profile described in this paper which extend for a hundred meters along the profile are termed as channel elements (or fifth-order surfaces) They are visible in Liulin outcrop because coarse sandstone above the surface and coal/mudstone below In different locations, they may be thin, but the con-trasts between a well-cemented sandstone or pebbly sandstone and underlying mudstone or coal are still obvious Macro-forms are ranked as fourth-order architectural elements and constitute the major subdivisions of the fifth-order channel element and accretionary cross-bedding are the most distinc-tive macroforms[28] The fourth-order surfaces are commonly convex-up, parallel to the accretionary bedding, or flat, trun-cated by erosion First- to third-order rank surfaces have not been distinguished in this study because of its small scale
4.2 Lithofacies Observation and classification of lithofacies are now stan-dard components of the facies-analysis methodology for studying sedimentary rocks In the Shihezi Formation, seven lithofacies and subfacies are recognized on basis of study of outcrop and core Shihezi Formation was subdivided into two lithofacies assemblages, including sand lithofacies and fine-grained lithofacies Individual lithofacies are listed in
Table 1, modified on classification of Rust and Jones[29]
5 Architecture elements Early attempts at the classification of architectural elements were developed by some researchers [30e33] A revised classification of fluvial architectural elements was provided by Miall[17]based on the former works Architecture elements analysis conducted in this study employ the classification of Miall [17] Sandy Bedforms (Element SB), Gravel Bars and Bedform (Element GB), Laminated Sand Sheets (Element LS), and Biochemical deposits of overbank environment were identified through Liulin outcrops survey
Fig 2 Regional stratigraphy of Ordos Basin (Modified from Ref [25] , 2003).
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Trang 45.1 Channel
In fluvial deposits, channels commonly have multistory fills
with each story bounded by an erosion surface and major
channels are bounded by fifth-order surfaces The Channel
element of Shihezi sand includes components of SB, GB, and
LS units The bounding surfaces and channel margins of Shihezi sandstones are completely exposed with cutbanks observed in outcrop
5.1.1 Sandy bedforms (element SB) Element SB is part of channel fills and constitutes 39.47% of the channel facies This element is composed of sand lithofacies
of Sp, Sh, Sw and Sm which result from the transport of sand by traction currents as bed load and in intermittent suspension
Individual sandy bedforms observed through outcrops in this study are about 4.3 me8.3 m in thickness (Fig 4a and b)
The sandstones in this element vary from fine-grained and medium-coarse-grained to coarse-grained; and locally contain scattered pebble Bedding in these facies consists of cross-bedding, ripple, massive, and faintly lamination
5.1.2 Gravel bars and bedforms (element GB) Facies channel bar constitute 11.31% of the channel facies
The gravel clastic sandstones are amalgamated into bars in several ways and three main methods of midchannel gravel bar
Table 1
Lithofacies in Shihezi sandstone, Ordos Basin, China.
Lithofacies
assemblages
Lithofacies
Sand Lithofacies Spe Matrix support, sand-granular-pebble sand ( Fig 3 g)
Sh Horizontal cross-bedded sand ( Fig 3 d)
Sp Planar cross-bedded sand ( Fig 3 c)
Sr Ripple, wavy and climbing-ripple sand ( Fig 3 f)
Sw Wedge cross-bedded sand ( Fig 3 e)
Sm Structureless to faintly laminated sand, massive sand ( Fig 3 a)
St Trough cross-bedded sand ( Fig 3 b) Fine-grained
Lithofacies
Fm Mudstone ( Fig 3 h and i)
Fs Fine grained sand ( Fig 4 c)
Fig 3 Lithofacies of Lower Permian Shihezi sands identified from cores (a) Grey medium-coarse massive sandstone, Well Zhao 15, 2950 m; (b) Ash grey trough
cross-bedded coarse sandstone, Well Tong 11, 2825.5 m; (c) Ash grey planar cross-bedded coarse sandstone, Well Shan 171, 3123.5 m; (d) Ash grey horizontal
cross-bedded coarse sandstone, Well Tong 11, 2879.8 m; (e) Green grey wedge cross-bedded coarse sandstone, Well Shan 144, 3241.78 m; (f) Dark grey ripple
argillaceous siltstone, Well Zhao 11, 3143.18 m; (g) Ash grey matrix support pebble sandstone, Well Zhao 20, 3068.1 m; (h) Dark massive mudstone, Well Zhao
28, 3157 m; (i) Dark grey mudstone, Well Shan 246, 3061 m.
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Trang 5construction were recognized by Ashmore [34] (1991).
Element GB are usually inter-bedded with lenses of
gravity-flow deposits and lithofacies such as Spe (Fig 4d) and is
characteristic of lithofacies St matrix support conglomerates
surveyed from the drilling core are commonly composed of
centimeter-scale clasts, from 1 cm to 3.6 cm in diameter
5.1.3 Laminated sand sheets (element LS)
Laminated sand sheets are composed of fine-grained
sandstones and thin-bedded shale with high clay contents
such as lithofacies of Sr (Fig 3f) Horizontal bedding or wavy
bedding develops This element is interpreted as a variant of
the channel element in which the channel is of low energy,
possibly undergoing abandonment and is filled by fine-grained
deposits [28,29] Element LS constitute tiny contents of the
channel elements, almost 0.22%
5.2 Overbank
Facies overbank constitute 4.8% of the channel facies Coal
and paleosols are typical components of biochemical
sedi-ments, which are symbols of architectural elements of the
overbank environment [17] Coal seams are typically
inter-bedded with fine-grained overbank sediments and may also
overlie or underlie crevasse-splay deposits and fluvial
channel-fill deposits (Fig 4b and d)
Fossil soil yield regarding climates and the evolutionary
patterns of fluvial floodplains Root traces, soil horizons, and
soil structures are the three main field features of paleosols
[35] Color and components of paleosols are related to climate
and source terrains [17] Black and dark-green mudstones (Fig 3i) indicate sedimentary environment of swamp and humid-semiarid climate
5.3 Floodplain 5.3.1 Floodplain fines (element FF) Facies floodplain constitutes 44.42% of the channel facies Floodplain fine sand consists of sheet like units It reflects the depositional surface as flat and may be traced laterally for more than 100 m [17] Element FF in this study can be investigated in outcrops with thickness of 3.3 m and fine grained sand (Fig 4c)
6 Characteristics of sands 6.1 Petrology and diagenesis Diagenesis phases including compaction, siliceous cemen-tation and carbonate cemencemen-tation have been studied by former researches [26,36] Compaction is concluded as the control factor of low permeability Whereas, dissolution is regarded as the positive effect to porosity increasing and is concluded as the control factor to the genesis of net pay
In our study, examination of Shihezi sandstones in thin section reveals a composition dominated by monocrystalline quartz (approximately 76% bulk volume) and lithic (up to 5%e45% bulk volume) Litharenite and lithic quartz sand-stone with less quartz sandsand-stone are the main rock types (Fig 5) Sandy bedforms (Element SB) and gravel bars and
Fig 4 Architecture elements identified from outcrops which are located in Liulin County, Shaanxi Province, China The exact location shown in Fig 1 Lower Permian Shihezi Formation is exposed and bounding surfaces are also indicated by arrows with rank numbers (a) and (b) Element of sand bedforms with thickness
of 4.3 m (a) and 8.3 m (b); (c) Element of floodplain fines with thickness of 3.3 m; (d) Gravel bars and bedforms with thickness of 3.15 m.
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Trang 6bedforms (Element GB) are the channel elements of high
energy and filled by bed-grained deposits including sand
lithofacies of Sp, Sh, Sw, Sm, Spe Poor-sorted deposits have
less content of quartz and high content of lithic and are
lith-arenite or lithic quartz sandstone (Fig 5) Fine grained
de-posits have high content of quartz and are mainly quartz
sandstones Laminated Sand Sheets (Element LS) and flood-plain fines (Element FF) including lithofacies of Fs are of low energy depositional environment and are well-sorted
Primary pores are less developed hampered by compaction
Secondary pores are well developed in coarse sands Inter-granular dissolution pores and interInter-granular secondary pores caused by phase transformation of feldspar to kaolinite were observed in microphotograph which results in positive effect
to porosity increase (Fig 6) Coarse sands characterized by matrix supports have been less infected by compaction and primary pore partly remains Remaining primary pores act as the accumulation space for sour fluids during the diagenetic process This may result in the intergranular dissolution and development of secondary pores Poor-sorted lithofacies of Sp,
Sh, Sw, Sm and Spe are formed in high energy channel with high deposition rates These sands have large scale grains which act as supporting matrix during compaction and then less hampered by compaction Primary pores partly remains in these sands which result in relatively high porosity
Whereas, fine grain sands with lithofacies of Fs and Sr do not have support from the grain matrix, and less primary pores left through compaction which result in less accumulation spaces for sour fluids and secondary pores are less developed due to less occurrences of dissolution Pore volume reduced during compaction and no increase through secondary diagenesis Thus, compared with fine grain sands, coarse sand has higher porosity and is favorable to be reservoir net pay
Fig 6 Examination of pore structure through thin section (Q: quartz; M: mica; K: kaolinite; P: pore; D: deformation of mica; E: enlargement of quartz) (a)
Intergranular dissolution pore (plane polarized); (b) Concavo-convex grain-to-grain contact caused by deformation of mica (perpendicular polarized); (c) Pore
reduction with quartz secondary enlargement (perpendicular polarized); (d) Phase transformation of feldspar to kaolinite with generation of intergranular pore
(plane polarized).
Fig 5 Constitutional diagram of sandstone components (Q: quartz; F:
feld-spar; L: lithic; Block 1: quartz sandstones; Block 2: litharenite quartz
sand-stones; Block 3: lithic sandsand-stones; Block 4: feldspar lithic sandstones.
Modified from Zhu [37] 2008).
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Trang 76.2 Electrofacies analysis
Well logging provide digitized information of full column
and has been an effective method for geological study In our
study, there is a good correlation between lithofacies derived
from core and well logging response Coarse sands formed in
point bar have typical well logging response of relative low
value of gamma ray log (Fig 7) As shown inFig 7, different
lithofacies have different logging responses Channel sands
including lithofacies of Spe, Sh, Sp, Sr, Sw, Sm and St have
relatively low GR response due to its poor content of shale
volume Channel bars and Bedforms (Element GB) composed
of lithofacies including St and Spe shows even lower GR
value Mudstone and horizontal cross-bedded sands in of low
energy currents have high shale volume and GR value in well
logging
In this work, well logging reveals that coarse sands can be
classified into two different types The first type of coarse
sands has relative low value of GR, SP and DEN and relative
low value of RLLD and RLLS Low value of GR, SP and DEN
can be interpreted as its higher porosity and permeability and
low value of RLLD and RLLS should be ascribed to its less or
no hydrocarbon content They should be interpreted as
sedi-ments of channel fills (Figs 8 and 9)
Besides characteristics of low values of GR, SP and DEN,
the second type of coarse sands have relative high value of
RLLD and RLLS According to well logging interpretation, these coarse sands have much higher porosity and perme-ability than type one and its high value of RLLD and RLLS indicates high content of hydrocarbon accumulated in pore Based on former study on facies and petrology, they should be sediments of channel bar (Figs 8 and 9)
6.3 Scale of sandstone bodies Width and spacing of the sand bodies are key factors to success rate of exploration well, and degree of interconnec-tedness determines the strategies of field development [17]
(Miall 1996)
In this study, mapping of sandstone bodies were conducted using data derived from a well-developed field (well spacing rang from 300 m to 800 m) Subsurface mapping reveals that channel sandstone bodies distribute widely from both lateral and longitudinal cross section profiles and have relatively poor connectivity (Figs 8 and 9) This indicates a frequent diver-sion of braided stream Channel sandstone is interbedded in floodplain deposits Multistory channel fill sandstone bodies have thicknesses ranging from 7 m to 18 m with an average of
12 m Channel width is estimated in range of 930 me1465 m with an average of 600 m through the dip oriented (WE) cross section profile Then width-to-thickness ratio is estimated to
be 50:1
Fig 7 Correlation between lithofacies derived from core and well logging response, showing well section of 3064 e3081 m, Well Zhao 20 Coarse sands have typical well logging response of low value of gamma ray log (VF ¼ very fine; F ¼ fine; M ¼ medium; C ¼ coarse) Lithofacies: (a) Horizontal cross-bedded sand (Sh), interlayered with ripple and climbing-ripple sand (Sr); (b) Upper, trough cross-bedded sand (St), lower, massive sand (Sm) to granular sand (Spe); (c) Sand-granular-pebble sand (Spe); (d) Planar cross-bedded sand (Sp); (e) Fine grained sand (Fs); (f) Mudstone (Fm).
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Trang 8Coarse-grained channel bars which have relative high
porosity, permeability and high hydrocarbon content are the
effective reservoir Coarse-grained channel bar sandstone
bodies have thickness ranging from 5 m to 8 m with an
average of 6.2 m; and its width ranges from 70 m to 130 m
with the mean value of 105 m Strike-oriented scale of coarse
grained channel bar sandstone bodies is estimated to be
230 me650 m, with the mean length of 475 m The geometry
of channel bar sand bodies can be depicted as an elongated
lens
7 Conclusions
This work presents an approach to architecture elements
analysis on basis of outcrops survey and quantitative
assess-ment to channel fills and channel bar sandstone bodies
Ar-chitecture elements including sandy bedforms (element SB),
gravel bars and bedform (element GB), and biochemical
de-posits of overbank environment and floodplain fines, were
identified from outcrops or cores The characteristics of
different elements (thickness, bounding surfaces and
lithofacies) were studied It can be concluded that the sedi-mentary setting of Lower Permian Shihezi Formation should
be braided river
Sandstone components and rock types were studied in detail Monocrystalline quartz with approximately 76% bulk volume and lithic up to 5%e45% bulk volume are the two main components Litharenite and lithic quartz sandstone with less quartz sandstone are the main rock types Examination through thin section reveals that secondary pore developed well in coarse sand
Scale of coarse grained channel fills and channel bar sandstone bodies are quantitatively estimated Subsurface mapping reveals that channel sandstone bodies distribute widely from both lateral and longitudinal cross section profile, and are poorly connected The geometry of channel bar sand bodies can be depicted as an elongated lens Width-to-thickness ratio of channel fills is estimated to be at 50:1
Lower Permian Shihezi sandstone is the main gas reservoir
of Ordos Basin This study did some work from the aspect of sedimentology and carried out some quantitative assessment for channel fills and channel bar sand bodies Intensive study
Fig 9 Mapping of sand bodies, showing poor connectivity and widespread distribution Strike-oriented cross-sections (NS) through Shihezi Formation, showing
longitudinal connectivity and scale of sandstone bodies (Channel fills composed of lithofacies including Spe, Sh, Sp, Sr, Sw, Sm and St; Channel bar composed of
lithofacies including St and Spe Modified from Miall [28] , 2003).
Fig 8 Stratigraphic interpretation of sandstone bodies through Shihezi Formation Dip oriented (WE) cross section, showing lateral connectivity and scale of
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Trang 9on reservoir heterogeneity and detailed reservoir model are
recommended for further work
Foundation item
Supported by China National Science& Technology Major
Project (2016ZX05062, 2016ZX05015-006); PetroChina R&D
Project (2014F-4701-03)
Conflict of interest
The authors declare no conflict of interest
Acknowledgments
The authors would like to thank Dr Lijuan Wang, Dr Na
Luo, Dr Hanqing Zhu and Dr Qunming Liu for numerous
discussions in the field and meaningful suggestions to this
work
References
[1] H.N Fisk, Geological Investigation of the Alluvial Valley of the Lower
Mississippi River, The Mississippi River Commission, Vicksburg,
Mis-sissippi, 1945, p 78.
[2] A.D Miall, Fluvial sedimentology: an historical review, in: A.D Miall
(Ed.), Fluvial Sedimentology Can Soc Petrol Geol Mem 5, Canada
Society of Petroleum Geology, Calgary, 1978, pp 597 e604.
[3] A.D Miall, Architectural-element analysis: a new method of facies
anal-ysis applied to fluvial deposits, Earth-Science Rev 22 (1985) 261 e308.
[4] A.D Miall, Architectural elements and bounding surfaces in channelized
clastic deposits: notes on comparision between fluvial and turbidite
systems, in: A Taira, F Masuda (Eds.), Sedimentary Facies in the Active
Plate Margin, Terra Scientific, Tokyo, 1989, pp 3e15.
[5] M.C Cuevas-Gozalo, A.W Martinius, Outcrop data-base for the
geological characterization of fluvial reservoirs: an example from distal
fluvial fan deposits in the Loranca Basin, Spain, in: C.P North,
D.J Prosser (Eds.), Characterization of Fluvial and Aeolian Reservoirs,
Geological Society Special Publication 73, Geological Society, London,
1993, pp 79 e94.
[6] O Dubrule, Estimating or choosing a geostatistical model? in:
R Dimitrakopoulos (Ed.), Geostatistics for the Next Century, Kluver
Academic Publishers, Dordrecht, Holland, 1994, pp 3 e14.
[7] O Falivene, P Arbues, A Gardiner, G Pickup, J.A Mu~noz, L Cabrera,
Best practice stochastic facies modeling from a channel-fill turbidite
sandstone analog (the Quarry outcrop, Eocene Ainsa Basin, northeast
Spain), AAPG Bull 90 (2006) 1003 e1029.
[8] F.P Ivan, H David, R Jonathan, A new approach for outcrop
charac-terization and geostatistical analysis of a low-sinuosity fuvial-dominated
succession using digital outcrop models: Upper Triassic Oukaimeden
Sandstone Formation, central High Atlas, Morocco, AAPG Bull 93
(2009) 795e827.
[9] T Dreyer, L.M Falt, R.K Høy, R Steel, J.L Cuevas, Sedimentary
ar-chitecture of field analogs from reservoir information (SAFARI): a case
study of the fluvial Escanilla formation, Spanish Pyrenees, in: S.S Flint,
I.D Bryant (Eds.), The Geological Modeling of Hydrocarbon Reservoirs
and Outcrop Analogs, International Association of Sedimentologists
Special Publication 15, 1993, pp 57 e80.
[10] C.P North, K.S Taylor, Ephemeral-fluvial deposits: integrated outcrop
and simulation studies reveal complexity, AAPG Bull 80 (1996)
811 e830.
[11] R Klingbeil, S Kleineidam, U Asprion, T Aigner, G Teutsch, Relating
lithofacies to hydrofacies: outcrop-based hydrogeological
characterization of quaternary gravel deposits, Sediment Geol 129 (1999) 299 e310, http://dx.doi.org/10.1016/S0037-0738(99)00067-6 [12] I.A Lunt, J.S Bridge, R.S Tye, A quantitative, three-dimensional depositional model of gravelly braided rivers, Sedimentology 51 (2004) 377 e414, http://dx.doi.org/10.1111/j.1365-3091.2004.00627.x [13] R Labourdette, R.R Jones, Characterization of fluvial architectural el-ements using a three-dimensional outcrop data set: Escanilla braided system, south-central Pyrenees, Spain, Geosphere 3 (2007) 422 e434,
http://dx.doi.org/10.1130/GES00087.1 [14] N Tayler, R.J Finley, Architecture controls on the recovery of hydro-carbons from sandstone reservoir, in: A.D Miall, N Tayler (Eds.), The Three-Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery: Concepts
in Sedimentology and Paleontology, vol 3, 1991, pp 1e5, http:// dx.doi.org/10.2110/csp.91.03.0001
[15] D Chen, X Pang, Z Jiang, J Zeng, N Qiu, M Li, Reservoir charac-teristics and their effects on hydrocarbon accumulation in lacustrine turbidites in the Jiyang Super-depression, Bohai Bay Basin, China, Mar Pet Geol 26 (2009) 149 e162, http://dx.doi.org/10.1016/j.marpetgeo 2008.03.003
[16] J.D.A Clarke, Influence of fluvial architecture assumptions on aquifer models: lessons from the Lower Balonne, southern Queensland, in: I.C Roach (Ed.), Regolith, CRC LEME, 2004, pp 62 e66.
[17] A.D Miall, The Geology of Fluvial Deposits: Sedimentary Facies, Basin Analysis and Petroleum Geology, Springer-Verlag Inc., Heidelberg,
1996, p 582.
[18] C.R Fielding, R.C Crane, An application of statistical modelling to the prediction of hydrocarbon recovery factors in fluvial reservoir sequences, in: F.G Ethridge, R.M Flores, M.D Harvey (Eds.), Recent De-velopments in Fluvial Sedimentology, Soc Econ Paleontol Mineral Spec Publ 39, 1987, pp 321e327.
[19] J.A Robinson, P.J McCabe, Sandstone-body and shale-body dimensions
in a braided fluvial systems: salt wash sandstone member (Morrison Formation), Garfield County, Utah, AAPG Bull 81 (1997) 1257e1291 [20] J.S Bridge, R.S Tye, Interpreting the dimensions of ancient fluvial channel bars, channels, and channel belts from wireline logs and cores, AAPG Bull 84 (2000) 1205 e1228.
[21] A.V Kjemperud, E.R Schomacker, T.A Cross, Architecture and stra-tigraphy of alluvial deposits, Morrison formation (Upper Jurassic), Utah, AAPG Bull 92 (2008) 1055 e1076.
[22] M Zhai, Chinese Petroleum Records, vol 12, Petroleum Industry Press, Beijing, 1992.
[23] J Yang, Tectonic Evolution and Petroleum Distribution in Ordos Basin, Petroleum Industry Press, Beijing, 2002.
[24] R Chen, X Luo, Z Chen, Z Wang, B Zhou, Estimation of dendudation thickness of Mesozoic stata in the Ordos Basin and its geological sig-nificance, Acta Geol Sin 80 (2006) 685 e693.
[25] Z He, J Fu, S Xi, S Fu, H Bao, Geological features of reservoir for-mation of Sulige gas field, Acta Pet Sin 24 (2003) 6 e12.
[26] J Nan, S Wang, S Liu, X Shi, S Wang, The contributing factors of lower porosity and permeability resevoir in permian in Sulige Gas field, Ordos Basin, J Northwest Univ Nat Sci Ed 35 (2005) 207e210.
[27] J.R.L Allen, Studies in fluvial sedimentation: bars, bar complexes and sandstone sheets (low sinuosity braided streams) in the Brownstones (L Devonian), Welsh Borders Sediment Geol 33 (1983) 237 e293.
[28] A.D Miall, B.G Jones, Fluvial architecture of the Hawkesbury sand-stone (Triassic) near Sydney, Australia, J Sediment Res 73 (2003)
531 e545.
[29] B.R Rust, B.G Jones, The Hawkesbury sandstone south of Sydney, Australia: Triassic analogue for the deposit of a large braided river,
J Sediment Petrol 57 (1987) 222 e233.
[30] D.G Smith, N.D Smith, Sedimentation in anastomosed river systems: examples from alluvial valleys near Banff, Alberta, J Sediment Pet 50 (1980) 157 e164.
[31] P.F Friend, Towards the field classification of alluvial architecture or sequence, in: J.D Collinson, J Lewin (Eds.), Modern and Ancient Fluvial Systems, International Association of Sedimentologists Special Publication 6, 1983, pp 345 e354.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130
Trang 10[32] P.J McCabe, Depositional environments of coal and coal-bearing strata,
in: R.A Rahmani, R.M Flores (Eds.), Sedimentology of Coal and
Coal-Bearing Sequences, International Association of Sedimentologists
Spe-cial Publication 7, 1984, pp 13 e42.
[33] N.D Smith, T.A Cross, J.P Dufficy, S.R Clough, Anatomy of an
avulsion, Sedimentology 36 (1989) 1 e23.
[34] P.E Ashmore, How do gravel-bed rivers braid? Can J Earth Sci 28
(1991) 326 e341.
[35] G.J Rettalack, Field recognition of paleosols, in: J Reinhardt, W.R Sigleo (Eds.), Paleosols and Weathering through Geological Time:
Principles and Applications, Geological Society of America Special Paper 216, 1988, pp 1 e20.
[36] D He, A Jia, C Tian, J Guo, Diagenesis and genesis of effective sandstone reservoirs in the Sulige Gas Field, Pet Explor Dev 31 (2004) 69 e71.
[37] X Zhu, Sedimentary Petrology, Petroleum Industry Press, Beijing, 2008,
p 113.
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2
3
4
5
6
7
8
9
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