permeability in fractured rocks - · pdf filepermeability in fractured rocks irwan iskandar,...

Permeability in Fractured Rocks
Irwan Iskandar, PhD KK Eksplorasi Sumberdaya Bumi
Teknik Pertambangan
Fakultas Teknik Pertambangan dan Perminyakan ITB

Irwan Iskandar Earth Resources Exploration Research Group Faculty of Mining and Petroleum Engineering
Institut Teknologi Bandung

Dual porosity
Secondary porosity as main actor
Rock defects/Fracture/gouge
Connectivity?
Heterogeneity
Isotropy / anisotropy
K value from field/lab. test?

Dual Porosity
-100 m
-110 m
Depth

Connectivity
heterogeneity
-100 m
-110 m
-120 m
K105 : high
Depth Connected
K115 : low
Not Connected

Anisotropy
West East

-100 m
-110 m
Laboratory test from core
NOT RELIABLE High K value (rock mass)
K is very low impermeable

Pumping Test
Result
Transmisivity (Permeability)
Storativity
Radius of Influence
Limitation and Problem
Need construction, observation well (obs. well),
Sometimes obs. well not at right position

25 m
100 m Pumping well
Observation well 1
Observation well 2
No drawdown
5 meter drawdown

Packer test
Can be test at an interval depth
No need well construction, nor obs. well
Suitable in fracture rocks
Result
Transmisivity (Permeability)
Type of rock defects (filled, blocked, open)
Packer Test

-100 m
-110 m
-120 m
K105
K115
Water enter rock formation easily
K >>>
Packer Test

-100 m
-110 m
-120 m
K105
K115
Very limited number of water can enter the rock formation
K

Another approach:
In a rock mass flow can be more like a porous medium (Long et al 1982)
Based on structure observation K can be approached by
e.g.
1) ODA method (1985, 1996) and
2)HC-System (2010)
Limited number of Field Hydrogeological Test
In fractured and heterogenic rock, laboratory test is not reliable

ODA-method Upscaling approach for fractured medium
Permeability tensor depend on geometrical properties of fractures
Aperture area (a)
size (length) / persistence (l)
orientation ()
l
a

If a fractured rock is treated as a homogeneous, anisotropic porous medium, the permeability tensor, obeying Darcy's law, can be formulated as (Bear, 1972)
If a fractured rock mass is assumed to have an impermeable matrix and groundwater is assumed to only flow through fractures, the apparent flow velocity can be defined as
Field Hydraulic Gradient in Geometry and size of cracks (fractures)
Joint apperture

The permeability tensor ki,j is concisely expressed by a symmetric, second-rank tensor P, (called the crack tensor) which depends only on the geometrical properties of related cracks (crack shape, aperture, size and orientation)

ODA-method
Can be used at
A specific area of opening/face/blocks
Problems and limitations
Not easy to measure (from borehole)
Aperture area (a)
size (length) / persistence (l)
orientation ()

HC System Empirical approaches
Rock Quality Designation (RQD)
Depth Index (DI)
Gouge Content Designation (GCD)
Lithology Permeability Index (LPI)

HC-System
RQD (Rock Quality Designation)
From geotechnical log
idea : low RQD (poor rock)more permeable (High K)
Note:
100 % RQD impermeable?
0 10 cm
0 100 cm

Core photograph shows fractured of Carbonaceous Shale
Above-left: open and unfilled joint/ crack; upper-right: highly crushed samples from SOP-80D bore bole; bellow: joints orientation which follow the bedding plane orientation.

Depth Index (DI)
Idea :
Many researchers (for example Lee & Farmer, 1993; Singhal & Gupta, 1999) pointed out that rock mass permeability may decrease systematically with depth.
LT is the total length of a borehole
Lc is a depth which is located at the middle of a double packer test interval in the borehole 0 < DI < 1
0
300 m
200 m
220 m
DI =?
HC-System
The greater DI, the higher permeability

Gouge Content Designation (GCD)
the permeability of clay-rich gouges has extremely low values (Singhal & Gupta,1999).
Idea: If the fractures contain infillings such as gouges, permeability of the fractures will reduce.
HC-System
Rs value is defined as the cumulative length of core pieces longer than 100 mm in a run
Rs the total length of the core run
RG is the total length of gouge content
The greater GCD will reduce the permeability of the core run.

Lithology is the individual character of a rock in terms of mineral composition, grain size, texture, color, and so forth.
HC-System

HC-System

Rock mass permeability system
HC value
Hyd
rau
lic C
on
du
ctiv
ity
(m/s
ec)

EXAMPLE

Physical Model (Database)
Hole ID ID X Y Z Bottom 1 Bottom 2 Bottom 3 Bottom 4 Bottom 5 Bottom n

Data (Physical Model)
Topografi
X, Y, Z (ASCII file) atau (.DXF) 3D polyline
Log Bor
ID, X, Y, Z (ASCII) atau (.DXF) 3D polyline
Hydrologic Features (River, Lake, Sea, Pond, Stream) in dxf
Hydrogeological Parameter (K, S, ,) dalam 3 D data
(X, Y, Z, K, S, ) atau (ID, Layer, K, S, )

Physical Model (Grid Cell Based)
stratigraphy unit is not a must
Each cell unit is translated to valued grid
Each cell is has one value (K, S, and other parameter)
Block model of the grid would hydrostratigraphical pattern
depend on the structure
Adjustment and interpolation were made by Hydrogeologist
A lot of Number of cells
Time of simulation is relatively long

y = 8E-06x - 5E-06
0,00E+00
5,00E-07
1,00E-06
1,50E-06
2,00E-06
2,50E-06
3,00E-06
3,50E-06
4,00E-06
0,5 0,6 0,7 0,8 0,9 1
Hyd
rau
lic C
on
du
ctiv
ity
(m/s
)
RQD Factor = (1-RQD/100) Linear (RQD vs K) Poly. (RQD vs K)
Hydraulics Conductivity and RQD
Higher Hydraulic
Conductivity
Higher RQD
Lower Hydraulic
Conductivity
Lower RQD

Model Dimension Distance Grid
Size
Grid
Sum
Total
Block Grid
Easting
(column)
Min 403500 2000 10 200
3,200,000
Max 405500
Northing
(row)
Min 306000 2000 10 200
Max 308000
Elevation Min 400
800 10 80 Max 1200
10 x 10 x 10 meter
Contoh Grid Cell Based

Bor ID X (m) Y (m) Depth (m) k (m/s) log k
GW-01 24300 -1200 6.4 1.14 10-5 -4.943
24300 -1200 12.5 5.08 10-6 -5.294
24300 -1200 20.6 2.77 10-4 -3.557
24300 -1200 28.0 1.81 10-5 -4.742
24300 -1200 33.1 5.47 10-4 -3.262
24300 -1200 35.6 1.82 10-5 -4.739
GW-02 37.2 2.89 10-4 -3.539
GW-03 23000 1000 3.3 1.50 10-5 -4.822
23000 1000 6.5 1.85 10-5 -4.732
23000 1000 7.7 8.22 10-5 -4.085
GW-04 23800 0 12.4 2.89 10-5 -4.538
23800 0 18.1 3.39 10-4 -3.469
23800 0 24.4 7.29 10-5 -4.137
23800 0 36.4 1.25 10-4 -3.903
23800 0 39.4 4.78 10-4 -3.320
GW-05 25000 -1100 6 2.08 10-5 -4.681
25000 -1100 11.1 3.24 10-5 -4.489
25000 -1100 21.2 7.41 10-5 -4.130
25000 -1100 23.2 1.85 10-5 -4.732
25000 -1100 29.1 1.50 10-6 -5.822
25000 -1100 47.1 2.08 10-5 -4.681
GW-06 22500 -2300 6.5 1.10 10-4 -3.957
22500 -2300 16.7 2.55 10-5 -4.593
22500 -2300 21.5 3.88 10-5 -4.411
22500 -2300 26 6.74 10-5 -4.171
22500 -2300 30.5 2.35 10-5 -4.628
22500 -2300 35.9 1.04 10-4 -3.981
22500 -2300 39.5 5.65 10-6 -5.247
CGW-07 23200 -2000 3.5 3.44 10-5 -4.464
23200 -2000 12.5 7.13 10-4 -3.147
23200 -2000 32.9 1.27 10-4 -3.895
23200 -2000 40.3 2.69 10-4 -3.570
CGW-08 22700 -1300 6.2 3.89 10-5 -4.409
22700 -1300 13.4 2.67 10-6 -5.573
Data (Physical Model) Grid Cell Based
Contoh Grid Cell Based Data

Number of data 95 Minimum value -5.57
Mean -4.40 First quartile -4.74
Standard deviation 0.68 Median -4.46
Coefficient of variation -0.15 Third quartile -3.40
Skewness -0.20 Maximum value -3.15
Statistical summary of log transf

permeability in fractured rocks - · pdf filepermeability in fractured rocks irwan iskandar,...

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