Page 1
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 22 (2017) pp. 12844-12851
© Research India Publications. http://www.ripublication.com
12844
The Development of Palaeokarst Systems in the Middle Miocene Carbonate
Reservoir, South Song Hong Basin
Phong Van Phung1*, Anh Vu The1 and Tung Nguyen Thanh1
1 Vietnam Petroleum Institute, Hanoi City, Vietnam.
*Orcid: 0000-0001-7298-7746 Abstract
Paleokarst systems are considered as one of the main factors
resulting in carbonate reservoir characteristics. Nonetheless,
few effictive workflows have been proposed to interpret the 3D
distribution of such systems. An integrated approach of 3D
seismic interpretations, attributes, well log sequence
stratigraphic analysis and nearby analogous fields has been
applied to reveal and understand numerous paleokarst features
in the Middle Miocene limestone preserved on the Tri Ton
high, South Song Hong Basin. Seismic scale mapping and
visualization of the paleokarst systems can be used to achieve
by interpreting circular. The typical seismic and geological
evidences of paleokarst development were observed clearly on
the top and slope of a regional uplift beneath an unconformity.
Images of paleokarst networks is demonstrated based on
erosional topography and seismic geomorphologic patterns for
sinkholes, rivers/canyons, and hills, revealing a mature surface
drainage system.
Keywords: Paleokarst, seismic attributes, seismic
interpretations.
INTRODUCTION
More than half of the proven hydrocarbon reserves in the world
are in carbonate reservoirs [5], which their reservoir features
such as palaeokarst networks, sinkholes, collapses and caves
play a significant role on producing hydrocarbon.
Karstification is, in general, a result of diagenetic processes and
independent of depositional characteristics, althrough it may
have been influenced by fractures and joints. The karstification
patterns may be existed extensively from pervasive with large
sizes of karst holes to more localized with a dentritic pattern or
even a footprint of a tiny bird. The results of several studies
have been not only recognized karst features but also map their
spatial distribution such as the Northern Marion Carbonate
Platform in Australia; the Luconia Platform, offshore Sarawak
in Malaysia [4]; and the Ngimbang and Kujung Formations of
Java in Indonesia [9].
Tertiary carbonates have been exceedingly appreciated in the
oil and gas industry within the Southeast Sea region, the Middle
Miocene Carbonate belong the South Vietnamese margin
included [6]. Though little explored, exploration of Middle
Miocene carbonates in the South Song Hong Basin, up to now,
has been focusing on by several hydrocarbon fields drilled.
Based on old available data in the area, there are abundant
paleokarst networks observed in the Middle Miocene carbonate
in the South Song Hong Basin, while adjacent rocks have good
petroleum generation conditions, with an excellent marine
caprocks overlaid. However, the 2D old seismic data is not
clear enough to map paleofeatures distribution because of its
low resolution and a large distance of 2D line spacing. In order
to investigate the prospect of buried hill carbonate reservoirs in
the study area (Figure 1), a high-resolution 3D survey and
geolocial analysis in term of well log sequence stratigraphic
correlation were carried out. It helps to understand and map the
growth of the palaeokarst distribution and provide ideal future
well locations to develop as well as produce hydrocarbon.
Figure 1: Regional map shows the outlines of main basins.
The red square indicates the study area (After Fyhn, 2013[3]).
Page 2
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 22 (2017) pp. 12844-12851
© Research India Publications. http://www.ripublication.com
12845
DATABASE AND METHODOLOGY
This study is mainly based on interpretation of more than 2000
km2 of 3D seismic data acquired by CGGVertas in 2012,
complemented with four wells. The 3D survey was covered
fully the study area with a dominant frequency of 35Hz and a
Xline/Inline spacing of 25mx25m. Moreover, four wells with
full raw log data can be used and integrated with seismic to
build up more detailed sequence stratigraphic correlation.
These data were used to interpret and understand the paleokarst
features in the study area under methodology following.
Arcording to the guideline of modern karstology and combined
with the available geological and seismc data, the structural
interpretation and reservoir characterization with
palaeotectonics and palaeogeography studies were carried out
for a more understading of karst development. The major steps
and techniques include: Seismic interpretation, Seismic
attribute analysis, 3D visualazation, Stratigraphic well
correlation and comprehensive evaluation.
CARBONATE KARST CONCEPTS
Representative near suface karst of soluble rocks was modelled
in a block diagram by Loucks (1999) (Figure 2) that was
reconstructed after investigation of modern cave systems and a
summary of work by several other authors (i.e, Ford and
Williams, 1989; Palmer, 1995; White et al., 1995). The scheme
represents the basic elements of a karst system. A exceptional
drainage system forms at a karst related unconformity on
carbonate strata and consists of surface rivers and streams
eroding into the carbonate host rock and commonly
disappearing into the cavern system below. Also, sinkholes and
tower karst are formed by erosion and dissolution along this
surface. In the shallow subsurface (phreatic and vadose zones),
cave development produces tubes, canyons, and chambers
(rooms), which commonly contain breakdown breccia and
cave-sediment fill. Cave sediments result mainly from
sediment originating outside the cave system and later being
transported into the cave.
Figure 2: A block diagram of near-surface karst terrain,
inclunding surface, phreatic, and vadose cave features (modifed
from Loucks, 1999; used with permission of AAPG).
Passages within a cave system can be stable for thousands to
millions of years, as long as the cave system is not buried in the
deeper subsurface (Loucks, 1999). On burial at greater depths,
the stress of the overburden will promote passage collapse
(Figure 3). The depth of collapse is quite variable where open
voids in karstified carbonates against depth was plotted, as
evidenced by bit drops during drilling (Loucks, 1999).
Figure 3: A schematic diagram showing the geometry and
component facies of a single cave passage buried in deeper sub-
surface where collapse and extensive brecciation occurred
(modifed from Loucks, 1999; used with permission of AAPG).
As the cave passage subsides into the subsurface, the ceiling
and walls collapse, forming more breccia (Figure 3). Also, as
the original void collapses, a damage zone forms around the
void, creating a much broader zone of breccias, fractures, and
faults (Figure 3) (Loucks, 1999). As burial continues, larger
blocks and slabs with voids between them will become
mechanically unstable and brecciate, thus increasing the
abundance of smaller clasts and decreasing large voids.
In areas where the density of cave passages is high, fractures
and faults have been considered as joints among individual
cave-collapse damage zones. The collapse of each cave passage
increases the cumulative effect of overall substance in the
lithified strata above (suprastratal deformation of Loucks,
2003), forming one large damage zone (Loucks, 2007). A
buried coalesced-collapsed paleocave system will therefore
consist of (1) numerous linear collapsedcave passages of
variable length and filled with breccia and sediment and (2)
broader damage zones of faults and fractures connecting these
collapsed tubes. The final product can be hundreds of meters
thick (includes both the karstified zone and the suprastratal
deformation above) and kilometers wide and long.
Page 3
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 22 (2017) pp. 12844-12851
© Research India Publications. http://www.ripublication.com
12846
RESULTS AND DISCUSSIONS
Generally, a surface of carbonate has a unique topography as
karst plain formed from the dissolution of soluble rocks such as
limestone or dolomite during the diagenetic histories. It is
characterized by underground drainage systems with sinkholes
and caves. The karstification of a landscape may result in a
variety of large or small-scale features on both the surface and
subsurface. On the figure 4, the dip angle of top structural
carbonate reservoir of the study area displayed in 3D view
presents several topographic carbonates features presevred,
including sinkholes, channels/dry valleys. They are the results
of diagenetic stages. These features have developed the whole
study area.
As Anh The Vu stated that the thickness of the Middle Miocene
platform carbonate developed over the Tri Ton High structure
decreases swiftly toward the East, Hoang Sa grabens due to
carbonate production limited in the deep marine environment
(Figure 5) [1]. According to seismic facies such as chaotic
features relating to plentiful collapses/sinkholes can be
observed clearly through the whole carbonate section and other
ones appear vertivally inside body of the carbonate interval
(Figures 5a and 5c). This could relate to the ancient water table
during diagenetic times [3]. These features are up to 500 m in
relief.
Figure 4: Paleokarst and Pore observed from conventional core and thin sections. Figure 11c shows vuggy features (After Hoang,
2015; used with permission of PetroVietnam Journal).
Figure 5: The dip angle of top structural carbonate reservoir in 3D view presents several topographic carbonate features such as
sinkholes, channels/dry valleys among the sur
Page 4
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 22 (2017) pp. 12844-12851
© Research India Publications. http://www.ripublication.com
12847
Seismic attributes have been provided important information
not only to understand but also to predict carbonate resevoir
properties such as karsts, collapses, sinkholes as well as
fractures. They can be interpreted on the basic of a reflection
terminals, geometry and morphology shown by continuity
slices. In this paper, Relative Acoustic Impedance, Trace
Envelope and Coherence seismic attributes were carried out
and used to analyze karst/sinkhole features. Figure 6, 7 are
horizontal slices of 100m beneath top carbonate from the
Realtive Acoustic Impedance attribute cube with impress karst
networks. Figure 8 is a comparison of palaecollapses among
Trace Envelope, Coherence attribute at 1800 depth slice and a
real sinkhole. All seismic attributes express karst networks
obviously. Individual collapsed-paleocave complexes in the
study area area vary in size and shape. Large collapsed-
cave/sinkholes have diameters ranging from 150 to 500 m and
height up to 300 m (including intrastratal and suprastratak
deformation) and are well above seismic resolution.
Figure 6: Seismic (a) and Geological section (b) is to present the carbonate interval capped by thick deep marine shale and
several palaeofeatures can be observed clearly.
Base Carbonate
Top Carbonate
1.0km 1.0km
2.0km 2.0km
1.5km 1.5km
2.5km 2.5km
a
A2
3km
1.0km 1.0km
2.0km 2.0km
1.5km 1.5km
2.5km 2.5km
Basement
Carbonate reservoir
Marine shale
A2
W E
b
3km
Base Carbonate
Top Carbonate
1.0km 1.0km
2.0km 2.0km
1.5km 1.5km
2.5km 2.5km
c
A2
Collapse/Karst features
W E3km
Figure 11
Page 5
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 22 (2017) pp. 12844-12851
© Research India Publications. http://www.ripublication.com
12848
Figure 7: The palaeofeatures such as dryvalleies, drainage systems is on the horizonal slice and to comapare to conceptal model
of palaeofeatures of carbonate rocks (a-Conceptal model of palaeofeature of carbonate rocks; b-a horizonal slice, c-seismic
section).
Figure 8: An example of 50-100m width of karst on the horizontal slice 2 below top of carbonate 100m.
Similar to 3D visualization, time-slice (horizontal slice) flying
is a significant powerful tool to map karst/collapse/sinkhole
features from top to bottom of carbonate reservoir. It allows
interpreter to look and scan into the 3D cube in multiple
directions and/or at different angles. Starting form the
calibration point, it is easy to trace amplitude or map karsts or
caves. Figure 9 shows the result of mapping karst features at
the time sclice. The karstification was observed and mapped
broadly and accurately excepted the areas which are influenced
by the shallow gas above.
Top Carbonate
Surface 1: Below100m Top Carbonate Time slice along Surface 14
Nab
c
Dry valley
Drainage features
The poor area due to
shallow gas accumulations above
2km
Well A4
Well A3
Well A2
(50-100m)
2
2
Top Carbonate
Plan view at 100m below Top Carbonate Line1
N
Well A4
Well A3
Page 6
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 22 (2017) pp. 12844-12851
© Research India Publications. http://www.ripublication.com
12849
Figure 9: Comparison karst/sinkhole features through the depth-slice at 1800m of seismic attributes (a-Coherence, b-Trace envelop,
d- seismic section) and a real sinkhole (c-400m diameter, 145-m-deep Great Blue Hole, Belize. Note the speedboat for scale).
Moreover, working with well log sequence stratigraphy is one
of aspects to understand and predict a development of karst
networks within the seismic sequence framework. According
to the principle of geological concept in term of log shape
charateristic, the Highstand systems tract (HST) and the
Transgress systems tract (TST) were defined and correlated
among these wells. Sequence boundary (SB) is considered as
the result of sea level droped below the shelf-break during the
Lowstand systems tract (LST). Sequence boundary
(Unconformity surface) then was formed as representative the
Lowstand system tract (LST). During LST, carbonate section
was exposed on the surface and eroded through diagenetic
times. Commonly, the karstification was developed along and
beneath the sequence boundary strongly. Figure 10 is a
conceptual welllog sequence stratigraphic correlation within
the seismic sequence stratigraphic framework.
Figure 10: The map of karst distribution on the horizontal slice below top carbonate 100m
(a-uninterpreted and b-Interpreted karst distribution)
According to information from well data such as welllog
interpretation, core image and thin section, the karst features
can be observed clearly. Figure 11 demonstrates the paleokarst
on thin section and welllog interpretation in term of small scale
vuggy associated with karst processes.
a b
dc
2km
2km
a b
Well A4
Well A3
Well A2
Well A4
Well A3
Well A2
Page 7
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 22 (2017) pp. 12844-12851
© Research India Publications. http://www.ripublication.com
12850
Figure 11: The seismic facies show probability system tracts developed on the study area.
To make a drilling decision, a comprehensive analysis for all
kinds of information is needed from the analysis for
hydrocarbon reservoir and surrouding features as well as the
palaeotectonic, palaeogeography. The balanced section can
reestablishrebuild the palaeotectonics and palaeogeography
environment; the seismic attribute cubes can be presented the
palaeochannels and palaeofeatures. The final results of the
comprehensive analysis are a 3D structure map and a karst
distribution map. From that future develoment and production
wells will be easy to locate and fit the future purposes
CONCLUSIONS
Integration of all available seismic and geological data shows
that the karstification was formed and developed in the whole
part of the Tri Ton high with complex features of karst,
collapses, sinkholes and obvious drainage systems on the
surface of carbonate. By combining different kinds of data, the
karst distribution could be mapped and expected well-
connected to locate the future wells.
The 3D seismic geomorphology of the surface paleokarst
drainage system is similar to that of modern karst drainage
systems. Interpreted geomorphologic and depositional
elements include channels/canyons that cut into the carbonate
terrain on the higher plateau in the upstream area, fluvial
valleys in the downstream area, numerous sinkholes that are
scattered throughout the area but are more clustered in the
updip area, and tower karsts and hills.
REFERENCES
[1] Anh The Vu, Michael Bryld Wessel Fyhn, Cuong
Trinh Xuan and others. Cenozoic tectonic and
stratigraphic development of the Central Vietnamese continental margin. Marine and Petroleum Geology
86 (2017), 386-401.
[2] Budd, P., Montgomery, J., Barreiro, B., Thomas,
R.G. Differential diagenesis of strontium in archaeological human tissues. 2000.
Appl.Geochem.15, 687–694.
[3] Cullen, A.B., Reemst, P. Henstra, G. and others.
Rifting of the South China Sea: new perspectives.
Petroleum Geoscience. 2010. 16, 273-282.
[4] Gartner, B.G.L., Schlager, W., and Adams, E.W.,
2004, Chapter 16: Seismic expression of the boundaries of a Miocene carbonate platform, Sarawak, Malaysia. AAPG Memoir 79, p. 351–365.
[5] Loucks, R. G., 1999, Paleocave carbonate reservoirs: origins, burial-depth modifications, spatial complexity, and reservoir implications: AAPG
Bulletin, v. 83, p. 1795–1834.
[6] Loucks, R. G., 2003, Understanding the development of breccias and fractures in Ordovician carbonate reservoirs. -in T. J. Hunt & P. H. Lufholm, The Permian Basin: back to basics, West Texas
Geological Society Fall Symposium: West Texas
Geological Society Publication No. 03-112, 231-252.
[7] Loucks, R. G., 2007, A review of coalesced, collapsed paleocave systems and associated suprastratal deformation. Time in Karst, Postjna. Page: 121-132.
[8] Michael B. W. Fyhn, Lars O. Boldreel andLars H.
Nielsen., 2013. Tectonic and climatic control on growth and demise of the Phanh Rang Carbonate Platform offshore south Vietnam. Journal of Asian
Earth Sciences. Page:152-168.
1400m
1800m
2200m
Well A3
1400m
1800m
2200m
HST/TST
Backsteping forward
TST
Depth(m)
Page 8
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 22 (2017) pp. 12844-12851
© Research India Publications. http://www.ripublication.com
12851
[9] Purwaningsih, M.E.M., Satyana, A.H., Budiyani, S.,
Noeradi, D., and Halik, N.M., 2002, Evolution of the late Oligocene Kujung reef complex in the Western East Cepu High, East Java Basin: seismic sequence stratigraphic study, Proceedings Indonesian
Association of Geologists (IAGI), 31st Annual
Convention, p. 655-671.