1. Addressing uncertainties in estimates of recoverable
gas for underexplored shale gas basins
Understanding the basic processes of hydraulic
fracturing, stimulation of natural faults and fractures,
and induced seismicity using numerical modelling
TNO Petroleum Geosciences, the Netherlands
Jan ter Heege, Unconventional gas team @ TNO

2. Upfront modelling and simulations of hydraulic fracturing
and gas production to quantify and reduce uncertainties
characterization hydraulic fracturing
basin modelling
natural fractures
gas production
TNO’s workflow to
determine
recoverable gas in
shale gas basins
upfront 
well-based estimates

3. Example application of workflow to underexplored shale
gas basin: the Jurassic Posidonia shale in the Netherlands

4. Limited (well log, core, seismic) data is available for
(uncertainty assessment of) estimates of recoverable gas
no wells targeting the Posidonia
no well tests or frac jobs
data from wells drilled through the
Posidonia (for example targeting
deeper Triassic tight gas sands)
current analysis based on data from
well WED-03, 3D seismics, core data
key aspect underexplored shales:
resource estimate, incl. uncertainty

5. Petrophysical and geomechanical toolboxes to
characterize bounds on relevant input parameters
Zone
ATBR
ATWDU
ATWDM
ATWDL1
ATWDL2
ATWDL3
ATWDL4
ATWDL5
ATWDL6
ATWDL7
ATWDL8
ATWDL9
ATWDL10
ATWDL11
ATWDL12
ATWDL13
ATWDL14
ATWDL15
ATWDL16
ATPO1
ATPO2
ATPO3
ATPO4
ATPO5
ATAL1
ATAL2
ATAL3
ATAL4
ATAL5
ATAL6
ATAL7
ATAL8
ATAL9
ATAL10
ATAL11
ATAL12
ATAL13
ATAL14
Underburden
Rock type
COARSE
OVER-BURDEN
SHALE
FINE
POSIDONIA
OVERBURDEN
UNDERBURDEN

6. In absence of well tests, bounds on local stresses are
determined using geomechanical theory
Bounds on Shmin:
-Hydrostatic pore pressure
Δ푃
Δ푧
=10 MPa/km
-Poisson effect of overburden
weight (normal faulting)
푆ℎ푚푖푛 =
휐
1−휐
푆푣 − 훼푃 + 훼푃
-frictional faulting theory (FFT)
(strike slip faulting, Shmax=Sv)
푆ℎ푚푖푛 =
푆퐻푚푎푥 − 훼푃
휇2 + 1
1
2 + 휇
2 + 훼푃

7. The fast commercial simulator MFRAC is used to test
sensitivity of fracture properties to input parameters
scenario input low base high
rock properties
permeability 0.19 3.36 16.04
leakoff coefficient 3.1 21.0 169.4
Young's modulus 5.7 8.5 19.7
Poisson's ratio 0.34 0.39 0.41
fracture toughness 0 2000 4000
stress state scenarios
vertical stress 43.7 48.3 52.8
min. hor. stress (extreme) 21.9 37.3 52.8
min. hor. stress (Poisson) 33.3 38.9 43.3
min. hor. stress (FFT) 27.0 30.4 52.8
treatment schedules
injection rate 1 10 20
total injection volume 10 250 500
number of stages 2 11 21
fluid/proppant type FR01/7140 FLD1/0001 H521/C002
total proppant mass 1 2 4
proppant injection ramp up constant 0.5x/1.5x

8. Hydraulic fracturing simulations for ranges of input
parameters show main variations of fracture properties
slickwater + 70/140
mesh proppant

9. Characterization of natural faults and fractures at
different length scales using different methods
seismic
outcrop
analogues
core plugs
thinsections
Fault length (m)
Cumulative number
Posidonia
Shale Fm
TNO
Torabi & Berg (2011)
faults from 3D
seismics
Whitby, UK
hydraulic fracturing

10. Variations in local stress field yield large variations in
stimulated natural fracture network
SHmax
Shmin
map views of
fracture network
increasing stress anisotropy
meters
wellbore
note different
scales

11. Variation in natural fracture spacing yield large
variations in stimulated natural fracture network
SHmax
wellbore
increasing fracture spacing
meters
Shmin
0.5 meter 2 meter 5 meter
map views
of fracture
network
(note
different
scales)

12. Optimization of hydraulic fracturing and well planning
based on subsurface faults and fractures

13. Primary fracture conductivities & propped fracture length
are used to test sensitivity of gas production to fracturing
frac job design
geological
uncertainty

14. BHP decline for sustained flow rates through evenly
spaced fractures along a 1 km horizontal well section
(closed reservoir system
MPROD simulator,
Meyer 2014)

15. Interference of gas flow from fractures shows optimum of
~10 fractures along a horizontal well section of 1 km
10

16. Gas production simulations for range of input parameters
show main variation of flow rates & cumulative production
hor. well section of 1 km
evenly spaced fractures
5-10-15 fractures
5-10-15 years production

17. Understanding the basic processes of hydraulic
fracturing, stimulation of natural faults and fractures,
and induced seismicity using numerical modelling
Jan ter Heege, Geomechanics team @ TNO
TNO Petroleum Geosciences, the Netherlands

18. KIP review
Finite difference modelling of stimulation of faults
and fractures
Pore
pressure
variation
within
intersecting
natural
fractures
Pore pressure
interference during
cyclic well tests
(coll. Renner, RUB)
coupled
modelling

19. Relation hydraulic fracturing and induced seismicity
Wassing et
al. 2013

20. Research hydraulic fracturing: Discrete element models
Goal: Predict “fraccability” and productivity of gas shales using
discrete element models and rock mechanical properties from lab
experiments and available well logs
Example: Discrete element
simulation of hydraulic fracturing
in rock sample by injection in the
centre of the sample (fractures are
visualized by blue/red discs)
Outcome: Fracture properties for different stimulation conditions
and (lateral & vertical variable) properties of gas shales

21. Discrete element modelling of hydraulic fracturing
a
• fluid domains based on
element topology
• pressure in fluid domains
• single phase fluid flow
over element-element
contacts (Darcy parallel
plates)
2D
3D
2D
3D
2D 2D
3D

22. characterization hydraulic fracturing
basin modelling
natural fractures
gas production