Exploring for Shale gas: Case study of the Tanezzuft Shale, Ghadames Basin, North Africa

2. INTRODUCTION
 Shale gas systems are self containing petroleum
systems (i.e. source, reservoir and seal all inclusive)
 They form continuous accumulation that is being
successfully exploited commercially in the US. This is
largely driven by government policy, technology and
rising natural gas price .
 Currently, natural gas production from shale gas plays in
the US stands at over 46% and it is projected to rise to
60% in the nearest future.
 The successful exploitation of shale gas plays in the US
have sparked up exploitation in Europe, North America ,
etc, where shale gas plays are thought to occur.

3. showing continuous shale gas accumulation (modified after Shenk and
Pollastro, 2002 )

4. NATURAL GAS IN SHALE PLAYS
 The composition of shale gas is dominantly methane,
with lesser percentages of propane, butane (Natural
gas)
 According to Kennedy et al. (2012), natural gas
commonly exists in shale reservoirs as:
 ‘free gas’ (in matrix pore network and natural
fractures),
 ‘Sorbed gas’ (adsorbed to Organic matter and natural
fractures or absorbed by the organic matter and
matrix pores) and
 ‘Dissolved gas’ (in liquid hydrocarbons)

5. NATURAL GAS IN SHALE PLAYS

6. COMPOSITION OF SHALES

7. AIM AND OBJECTIVES
• Organic richness (TOC) of Tanezzuft gas shale
• Type of Kerogen present in the gas shale
• Thermal maturity and thermal maturity history / distribution
• Relative proportion of clay minerals, quartz and calcite
• Comparison of Tanezzuft shale properties with established
shale gas plays in the USA

8. GHADAMES BASIN BACKGROUND
• ‘Large Intracratonic - Sag
basin’ (about
350,000km2) covering
parts of Tunisia, Algeria
and Libya.
• Basin fill: 8000m
• Conventional hydrocarbon
Reserves: 32BBOE
• Ongoing exploration for
Shale gas resources in
the Tunisian end of the
basin.
• Estimated resource 80-
120TCF (Troudi et.al,
2012)Ghadames Basin
(modified after Underdown and Redfern, 2008)

10. TANEZZUFT SHALES
• Deposited in the Early Silurian
at the onset of widespread
flooding in a Passive Margin
tectonic setting
• World class source rock
– Dominantly Type 2 kerogen
– present day TOC (0.5% to >
15%)
– HI values (250-450mgHc/g).
• 3 major lithostratigraphic units
– Quartz rich upper layer
– Calcite rich Intermediate
layer
– Basal clay rich hot shale
(best source rock quality)
Tanezzuft
Shales
Ghadames Basin Stratigraphy
(after Yahi et al, 2001)

11. Data set available
• Data (TOC data, Maturity data,
HI) from 37 wells was used for
this study.
• Some data was obtained from
Underdown (2006), Basu et al.,
(1997) and Yahi et al., (2001)
SHALE GAS EXPLORATION
WORK FLOW

12. INITIAL TOC WITH 2% CUT OFF
Initial TOC conversion formula
(Daly and Edman, 1987)
Initial TOC generally
increases towards the
west
latitude longitude
N
Initial TOC 3D Surface Map

13. Ro = 0.0180 x Tmax – 7.16
maybe unreliable where S2
values are <0.2(mg HC/g Rock)
THERMAL MATURITY (≥ 1.0% RO)
Latitude
Longitude
Thermal maturity
generally increases
towards the west
(Jarvie et al., 2001)
Thermal Maturity 3D Surface Map

14. SWEET SPOT
Wells used for Basin
Modelling
ONE-1 Well
BRD-4 Well
‘Combining initial
TOC map (2% TOC
cut off) with the
thermal maturity
map (1% Ro cut-off)’

15. BASIN MODELLING KEY INPUT
PARAMETERS
• Heat flow model
Underdown and Redfern (2008)
Event Begin
Age
(Mya)
Eroded
thickness
(m)
Alpine 36.7 100
Austrian 120 600
Hercynian 292 3600
Dixon et al., (2010) and Underdown (2006)
• Amount of exhumed
overburden

16. HEAT FLOW MODEL CALIBRATION

17. BURIAL HISTORY PLOTS
BRD-4
ONE-1

18. ADSORPTION POTENTIAL
SCHEMATIC
Pore Pressure (PSI)
AdsorptionPotential

19. COMPARISON
After Troudi et al., 2012

20. COMPARISON

21. CONCLUSION
•Identification of areas with sufficient organic richness (i.e. >2% initial
TOC).
•Tanezzuft gas shale is predominantly of oil prone Type II Kerogen
•1D maturity modelling reveal Tanezzuft shale to be in wet gas stage -
main stage of gas generation around the ‘sweet spot’
•Interbeds of quartz rich silt and fine sands exist in the Tanezzuft shale
stratigraphy. Its thickness increases towards the ‘sweet spot’
•The Tanezzuft shale shares a lot of similarity with the Marcellus and
Utica shales

22. CONFIDENCE/ PROBABILITY MATRIX

23. RECOMMENDATIONS
 Evaluation of the Mineralogy of the Tanezzuft Shale
 Investors should bare in mind the following questions:
• Is there adequate supply of water?
• What are the likely environmental issues to face?
• Is there adequate infrastructure?
• Are specialized oil field services readily available?
• Is there political backing for exploration?

24. ACKNOWLEDGEMENTS
•Thanks to God for his grace
•Mr James Armstrong for his wonderful supervision
•Other members of staff for support and encouragement
•Plate River Associates (BasinMod Software)
•TETFUND for sponsorship
Thanks for Listening