Sedimentary Facies of the Coal-bearing Walloon Coal Measures in

Tipton Field, Surat Basin

Yong Yang

, Aifang Bie

, Hanyu Bie

, Ming Zhang

, and Zhaohui Xia

Research Institute of Petroleum Exploration and Development, Petrochina;

School of Energy Resources, China University of Geosciences (Beijing)

Email: yangyong@cnpcint.com

Keywords:

Geometry, coal ply, coalbed methane, sedimentary facies, geological model

Abstract: The Walloon Coal Measures(WCM) is the main producing formation in Tipton coalbed methane(CBM)

field in the Jurassic Surat basin of the southeast Queensland, Australia. The numerous, thin, pinching out,

merging, and splitting coal seams in the WCM show highly variable in the spatial continuity. Accurate

determination of the facies, lithological attributes and geometries is important in the CBM exploration and

development planning for Tipton field. In the paper, high resolution sequence stratigraphy is used to build

an isochronal stratigraphic framework of sublayers and coal plies by utilizing all available data from cores

and logs. The key methodology in this procession is to identified single fining-upwards cycles with

sandstone at the bottom and coal, siltstone or shale at the top. Five lithologies of coal, shaly coal, sandstone,

siltstone and shale are classified by density and gamma ray well logs. Six members, 20 sublayers and 125

single coal plies are picked and correlated for the whole WCM. The distributions and geometries of coal and

channel are analysed for each sublayer. The characteristics of the following depositional facies are

interpreted: coal swamp and swamp, major channel, minor channel, floodplain, lacustrine. A concept model

of sedimentation is reconstructed to emphasize the relationships of major facies which is essential for the

further geological modelling, potential sweet spots determining and filed development of the Tipton field.

1 INTRODUCTION

Tipton coalbed methane (CBM) field is in the central

part of Surat Basin, Queensland, Australia. It covers

an area of 200 km

and the structure is a southwest

dipping unicline with two near-vertical faults

developed in the north area (Figure 1). A total of 167

wells are drilled and most of them have log data

such as LSD, SSD, gamma ray. The average well

distance is about 600m.

The target formation of the Tipton field is the

Walloon Coal Measures (WCM), which is the main

coal-bearing formation and CBM producing interval

in the Surat basin (Bohacs and Sutter, 1997). WCM

is a formation of middle Jurassic underlain by the

Eurombah Formation and Hutton Sandstone and

overlain by the Springbok Sandstone (Figure 2).

Juandah and Taroom are two main sedimentary

members of WCM with Tanglooma sandstone in

between. The individual seam packages within the

Juandah coal measures are Kogan, Macalister,

Wambo and Argyle. The Taroom has two

recognized coal seams: UpperTaroom and

Condamine which is the thicker and deepest seam.

The WCM consists coal-rich mire and a fine-

grained meandering fluvial system which develops

interbedded sandstone, siltstone, carbonaceous

mudstone, shale and coal (Fielding, 1993). The coal

is low rank with the vitrinite reflectance of 0.4-0.6%

and the net coal thickness is 20-30m deposited in a

fluvial sedimentary system. Many coal plies are

developed with splitting, merging, pinching out and

show highly variable in the spatial continuity.

Moreover, not much knowledge except Tangalooma

sandstone is known about the sandstone channels in

WCM, which have much influenced on the coal beds

continuity and the behaviors of CBM.

Due to these complicated geology, the paper uses

high resolution sequence stratigraphy to build an

isochronal stratigraphic framework of sublayers and

coal plies, and identifies five lithologies to analyze

the distributions of the coal ply and sandstone. The

depositional facies including channel, floodplain,

lacustrine, coal swamp and swamp are characterized

and the concept depositional model is built to better

Yang, Y., Bie, A., Bie, H., Zhang, M. and Xia, Z.

Sedimentary Facies of the Coal-bearing Walloon Coal Measures in Tipton Field, Surat Basin.

In Proceedings of the International Workshop on Environment and Geoscience (IWEG 2018), pages 233-238

ISBN: 978-989-758-342-1

233

understand the coal heterogeneity and the

relationships of these major facies.

Figure 1: The structure of Tipton field.

Figure 2: WCM formation of Surat basin.

2 METHODOLOGY

This methodology constitutes a systematic and

effective workflow to delineate the characteristics of

the coal ply and sandstone, and the distribution of

the depositional facies.

Firstly, all wells in the gas field are investigated,

including core data analysis, depth shifting, logs

normalization, lithology and facies interpretation.

Then the ply and sandstone are correlated and the

isochronal stratigraphy framework is built. The

correlation is based on the fining-up sequence cycle,

in which the sandstone bodies are the fluvial

channels at the base then the flooding plains of

siltstones upwards and then the development of the

lacustrine clays and coal swamps. The roof and floor

of the coal plies are manually picked in well section

in order to descript the splitting and merging of the

coal plies in areal and vertical directions. The

boundaries of the sandstone are also picked in order

to better improve channel description quality.

Based on the core descriptions, photographs and

logs of all wells, lithologies and sedimentary facies

are studied to describe the fluvial depositional

system in the gas field. The horizontal distributions

of the coal ply and sandstones are mapped. The

geometry parameters such as the coal thickness, the

area of coal distribution, the width, orientation,

amplitude, wavelength of the channel belts are

studied.

Then finally, the concept depositional model is

generated in which channel, floodplain, lacustrine,

coal swamp and swamp are integrated to describe

the interrelationships of these facies and to improve

the understanding of swamp heterogeneity in fluvial

system.

3 WCM THREE-ORDER

CORRELATION AND

ISOCHRONAL

STRATIGRAPHIC

FRAMEWORK

Correlation within the WCM package are complex

with an absence of marker beds and significant

lithological variations across small aerial distances

(Zhou, 2017). Individual seams are generally not

easy to be correlated due to the very high frequency

of seam pinches, swells, coalescence and

truncations.

For WCM isochronal correlation, a three–order

cycle correlation methodology is used to complete

the work guided by sequence stratigraphy theory.

The correlations in three-order cycle are made on the

basis of log comparison, using similar coal seams to

correlate over short distances and fining upward

IWEG 2018 - International Workshop on Environment and Geoscience

234

packages to correlate over longer distances. The first

order is the correlation of wells between coal

members, and then the sublayers. The third order is

the correlation of wells of single coal ply and

sandstone within each sublayer.

For the coal member division, the best markers

are the Macalister and Condamine which are

considered massive and relatively continuous

(Hamilton, 2014). There is often a gamma baseline

shift between the Macalister and Wambo seam

packages, with an increase in gamma response in the

Wambo. The Tangalooma sandstone at the base of

Argyle can also be regarded as a marker for its

relative lateral continuity.

The Kogan package which is the uppermost of

WCM generally contains one to three coal seams.

The Macalister package generally consists of one or

two well-developed seams and the highest

percentage of coal with a number of smaller

stringers. The Wambo generally consists of thin,

poorly correlatable coal seams. The Argyle package

usually consists of one or two major coaly intervals

with banded coals and muds, and Tangalooma

sandstone is at the base of Argyle which may be

continuous and consists of individual sand lenses in

some area. The Upper Taroom package is generally

a thick zone of thin coal seams, and forms a

relatively thick and continuous single seam at the

base. The Condamine is occasionally present as a

well-developed single seam up to 10m thick.

Sublayer is the general result of one fluvial

decrease period. The sandstone bodies are the fluvial

channels at the base then the flooding plains of

siltstones upwards and then the development of the

lacustrine clays and coal swamps. For sublayer

correlation, the typical single fining upwards cycle

with coal, clay or siltstone at the top and sandstone

at the base. The total of 20 sublayers are picked and

correlated for the whole WCM.

A ply refers to an individual depositional coal

seam and often quickly splits, merges or pinches out

laterally due to the sedimentary complexity. A total

of 125 coal plies, 54 sandstones are divided and

correlated in all 20 sublayers of the six members.

Figure 3 shows the plies correlation in sublayer3 of

Wambo member. Four fining upwards cycles (in red

triangular) are identified with the normalized density

and gamma ray logs. In each cycle sandstones are

divided and plies are picked for correlation. Three

sandstones are picked and the only lowest seems

continuous. The six correlated coal plies show the

high degree changing of lateral heterogeneity.

From members, sublayers to plies, the three-

order sequence stratigraphy correlation framework

are built for the whole WCM in Tipton field.

Figure 3: Coal ply and sandstone correlation.

4 COAL AND SANDSTONE

DISTRIBUTION

Based on the isochronal stratigraphic framework, the

thickness of each ply in each sublayer at well points

are summarized. The main thickness of coal plies is

about 0.5m, and only a few coal plies have the

thickness larger than 5m in WCM of Tipton field

(Figure 4). The horizontal thickness surfaces of each

ply are mapped with the coal ply thickness point

data. From these surfaces the maximum coal ply

thickness and the areal coal area can be picked. Thus

the correlation between coal ply thickness and the

extension area is established (Figure 5). It can be

seen that the coal seam area increases with the ply

thickness.

Figure 4: Histogram of coal ply thickness.

Sedimentary Facies of the Coal-bearing Walloon Coal Measures in Tipton Field, Surat Basin

235

Figure 5: Relationship between coal area and ply

thickness.

The sandstone thickness surfaces are also created

using the thickness from well points. From these

surfaces the channel belts can be identified. Figure 6

is the thickness surface of M1-sand. The red lines

show the major channel, the brown lines the minor

channel and yellow lines the crevasse splay. The red

arrows are the provenance direction. Then the key

parameters such as the amplitude, orientation, width

and wavelength of the channel belts can be obtained.

Table 1 is the parameter summary of major

sandstones in each sublayer of Tipton field. The

main orientation of the channel is from north to

south, and the width is 700- 1500m. The channel

amplitude is 800-1900m, and the wavelength is

1400-4000m. These channel geometry parameters

are important inputs for the facies object modelling

in the future research.

Figure 6: The sandstone thickness surface of M1-sand.

Table 1: The parameters of the channels of each sublayer

Memb

Sand

name

Orientation

Amplitude

(m)

Wavelength

(m)

Width

(m)

Thickn

ess (m)

Kogan

K2-sand

E, E 1000 1800

1000-1500

3-12

K1-sand

W, N 1200-1800

1900-4000

1200-1500

3-20

Macalist

M3-sand

W, N 1000-1200

2000-3000

1000-1200

2-15

M2-sand

1200-1500

2500-2700

1000-1400

2-10

M1-sand

, NW 1100-1300

1800-2700

1300-1500

5-20

Wambo

W4-sand

, NW 900-1000

1900-2000

1000

2-10

W3-sand

1000 2400

800

4-10

W2-sand

, NW, NE 1000 2400-2600 1200 2-12

W1-sand

E, NW, N 1000 2200-2400 900-1200 4-15

Argyle

A4-sand

E, NW 1000 2000-2200 1000-1200 3-15

A3-sand

E, N 1000 2000-2600 800-1200 4-12

A2-sand

E, N 800-900 1900-2200 700-900 4-12

A1-sand

W, N 800-1500 2000-2100 700-900 3-16

Upper

Taroom

T4-sand

W, N 1000-1900 1800-3000 900-1000 4-17

T3-sand

1000-1300 1600-2100 1000-1300 3-16

T2-sand

800-1000 2200-2500 800-1000 2-16

T1-sand

W,NE 900-1200 1900-2400 1000-1200 4-16

Condam

ine

C3-sand

900-1000 2300-2600 1100-1200 4-16

C2-sand

, NE 1000 1400-2000 800-1200 2-13

C1-sand

, NE 800-900 2400 1100-1200 1-10

5 MAJOR FACIES FEATURES

AND GEOLOGICAL CONCEPT

MODEL

The calibrated facies features of coal-bearing fluvial

system are summarized by combination of core

sample data, lithology log, mud log description,

lithology report and normalization logs (Hoffman,

2009). Six depositional facies are interpreted as

major channel, minor channel, floodplain, coal

swamp, swamp and lacustrine. The lithologies of

coal, shaly coal, siltstone and shale are

approximately corresponded the facies of coal

swamp, swamp, floodplain, lacustrine, respectively.

The sandstone is for the facies of major channel and

minor channel considering the thickness (Martin,

2013). Major channel thickness is usually large than

5m. Note that some thick crevasse splays could have

been interpreted as minor channel. Figure 7 is the

well section interpreting the distribution of the facies

between wells. The red star is the eroded coal by

channel, and the red triangular is the coal overlain on

the abandoned channels. The coal plies severely vary

in lateral with the splitting, merging, pinching out, or

erosion by channels.

Figure 7: Geological concept model of coal-bearing

environment.

IWEG 2018 - International Workshop on Environment and Geoscience

236

5.1 Coal Swamp and Swamp

Coal swamp and swamp are deposited in the

flooding plain. Coal swamp was relative pure coal

and swamp was the coal with shaly or siltstone

which may be more influenced by major or minor

channel system than coal swamp. The coal swamp

facies formed sheet-like deposits which rarely

exceeded 3m in thickness and usually ranged from

0.1 to 2.0m. They are usually underlain by shallow

water, and in some instances they are interbedded

with each other to form coal seams which may

occasionally exceeded 5m in thickness. Channel

system usually has great influence on the geometry

of the coal swamp and swamp (Stuart, 2014).

Usually the coal seams are eroded by the channels,

and coal can also deposit in the abandoned channels.

5.2 Channel

Channel deposits in WCM of Tipton field are

dominated mostly by sandstones which form long

belts tens of kilometers long from the north

direction, with typically 700- 1500m wide, mostly in

1000-1200m width and 2- 20m thick, although they

may occasionally exceed these dimensions (Shields

and Esterle, 2015). Major channels usually has the

thickness larger than 5m and sandstone is

dominating. Minor channel refers to the thickness

larger than 2m and sandstone is major. In Tipton

field the sandstone in both channels is generally fine

grained, and sometimes medium to coarse

sandstones may present. The major and minor

channels may include crevasse splays and levee

bank with relatively fine sandstone, which are

difficult to separate them from channels.

5.3 Floodplain

The floodplain is the background facies including

commonly fine-grained siliciclastic rocks such as

siltstone, mudstone, shale. Even levee bank and

crevasse splay which are not easy to separated are

also included in the floodplain facies. Sometimes

thin and isolated shaly coal is also included in some

places in the Tipton field.

5.4 Lacustrine

Dark, gray shale, claystone or siltstone in shallow

water are the main lithologies in the lacustrine. The

sedimentation rates and energy are low, and the

sediments generally occur as sheets which ranged

from a few centimeters to a few meters in thickness.

The organization of the major facies of the WCM

depositional environment is summarized in Figure 8,

which is a simplification and synthesis of geological

concept facies models. Major channels of variable

sinuosity are the main pathways of sediment

dispersal across the floodplain. These major

channels feed a hierarchy of minor channels,

crevasse splays and levee bank, depositing

sediments in floodplain. Sediments infilling the

shallow water, abandoned channel systems and

floodplain enable conditions to be established in

which coal could form and develop.

Figure 8: Geological concept model of coal-bearing

environment.

6 CONCLUSIONS

The isochronal stratigraphic framework of sublayers

and coal plies in WCM of Tipton field is built using

high resolution sequence stratigraphy, and the

geometries, distributions and interrelationships of

the coal plies and channels are obtained to better

reveal the lithology heterogeneity and continuity. A

number of sedimentary facies have been identified

and geological concept model is built which would

enhance the understanding of the depositional

environments of Tipton field.

ACKNOWLEDGEMENTS

The authors would like to thank the support of

Arrow Energy and Department of Asia and Pacific

E&P, RIPED, Petrochina.

Lacustrine

Floodplain

Lacustrine

Major channel

Minor channel

Crevasse splays

Coal eroded by channel

Coal in abandoned channel

Coal pinch out and split

Sedimentary Facies of the Coal-bearing Walloon Coal Measures in Tipton Field, Surat Basin

237

REFERENCES

Bohacs K and Sutter J 1997 Sequence stratigraphic

distribution of coaly rocks: fundamental controls and

paralic examples. AAPG Bull 81 (10) 1612-1639

Fielding C R 1993 The middle jurassicWalloon Coal

Measures in the type area, the rosewood Walloon

coalfield, SE Queensland. Aust. Coal Geol 9 4-15

Hamilton S K, Esterle J S and Sliwa R 2014 Stratigraphic

and depositional framework of the Walloon Subgroup,

eastern Surat Basin, Queensland. Aust. J. Earth Sci.

61(8) 1061-1080

Hoffman K L, Totterdell J M, Dixon O, Simpson G A,

Brakel A T, Wells A T and McKellar J L 2009.

Sequence stratigraphy of jurassic strata in the lower

Surat Basin succession, Queensland. Aust. J. Earth

Sci. 56 461-476.

Martin M A, Wakefield M, MacPhail M K, Pearce T and

Edwards H E 2013 Sedimentology and stratigraphy of

an intra-cratonic basin coal seam gas play: Walloon

Subgroup of the Surat Basin, eastern Australia. Pet.

Geosci. 19 21-38.

Shields D and Esterle J 2015 Regional insights into the

sedimentary organisation of the Walloon Subgroup,

Surat Basin, Queensland. Aust. J. Earth Sci.62 949-

967.

Stuart J, Moundney N P,McCaffrey W D, Lang S and

Collinson J D 2014. Prediction of channel connective

and fluvial style in the flood basin successions of the

Upper Permian Rangal Coal Measures (Queensland).

AAPG 98(2) 191-212.

Zhou F, Shields D, David T, Tyson S and Esterle J 2017

Understanding the geometry and distribution of fluvial

channel sandstones and coal in the Walloon Coal

Measures, Surat Basin, Australia. Marine and

Petroleum Geology 86 573-586

IWEG 2018 - International Workshop on Environment and Geoscience

238