presentation 021110
TRANSCRIPT
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Horizontal Wells: What WeKnow and What We Will
Never Know
Dr. S.D. Joshi
Joshi Technologies International, Inc.
Tulsa, OK 74135
Email: [email protected]
Website: http://www.joshitech.com
http://www.joshioilandgas.com
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Reservoir Applications
Naturally fractured reservoirs
Austin Chalk
Bakken Shale
Formations with water & gas coning
Gulf of Mexico
Elk Hills, California
Heavy oil reservoirs/Thermal application
California
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Reservoir Applications
Depleted gas/Gas storage reservoirs
Oklahoma
Texas
Low permeability shale gas reservoirs
Barnett, Woodford, Haynesville, Fayetteville,Marcellus, etc.
Waterflooding/CO2 flooding
California
East and West Texas
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U.S. Annual Horizontal Completions – Formation Summary
0
500
1000
1500
2000
2500
2007 2008 2009
YEAR
N U M
B E R O
F
C O M
P L E T I O N S
Bakken Barnett Cleveland Fayetteville
Haynesville Marcellus Woodford
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U.S. Horizontal Completions - State Summary
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History of Horizontal Drilling
Short radius drilling
Medium radius, 1985
Downhole mud motors
Re-entry drilling, 1995
Coiled tubing drilling(underbalance drilling)
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History of Horizontal Drilling
RSS: Rotary Steerable System
Fracture stimulation of horizontal wells
Open hole fracturing
Cased hole fracturing
Simo fracs
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Productivity Improvement Factor Distribution of Productivity in 96 horizontal wells
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Horizontal Wells Drilled in Western Canada
(1988-2001)
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The productivity improvement factor (PIF)ranges from 3 to 5. The short term PIF = 4.
The long term PIF = 1.8.
After 5 years of production, the cumulative oil
production from horizontal wells is about 2times greater than the cumulative production
from vertical wells.
About one in three horizontal wells has been
an economic failure. Thus economic successrate for horizontal wells is 66%.
Comparison of Horizontal and Vertical Wells
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Review the Field Results
Horizontal wells are mostly developmental(in-fill) wells
Commercial success ratio is 65 to 80%
Commercial success rate
Oil & gas price
Production rate
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North Slope, Alaska
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Bakken wells: 2008(8 fractures per well)
0
200
400
600
800
1000
1200
I
. P .
( B O P D )
1 2 3 4 5 6
VARIOUS WELLS IN BAKKEN SHALE
INITIAL PRODUCTION RATES
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Horizontal Well Rates
Stabilized rates of horizontal wells are 2 to 4fold more than stabilized rates of verticalwells.
Rates of fracture stimulated wells are 5 to 11times more than conventional wells.
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Horizontal Well Rate:
Important Parameters
Producing well length (Not the drilled length)
Formation damage/stimulation
kv/kh (vertical to horizontal permeability)
Reservoir permeability, kh
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Horizontal Well Rate:
Important Parameters
3 additional unknowns in fractured horizontal wells:
Number of fractures (producing)
Fracture conductivity
Fracture length
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Measurements
What can we measure?
Well rate
Well testing ( If practical)
Build up or drawdown
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Early Times Late Times
Horizontal Pseudo-Radial FlowVertical Radial Flow
mqB
k k Lv y1
162 6
. k v
k x
k y
Field Units
Metric Units Replace constant ‘162.6’ by ‘2.149 x 106’ in above equations
hk k
qBm
y x
6.1623
Horizontal Well Testing
Concepts
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Maximum three measurements
Rate
Slopes m1 & m3
We have at least 4 unknowns and
possibly 7 unknowns
Producing length, kv/kh, kh,
Skin factor ,Sm (damage or stimulation)
Results
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Results
Every answer is a right answer!
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Multiple Wells in The SameReservoir
Most reservoir properties show log normaldistribution. Therefore, productivity of several
horizontal wells drilled in the same reservoir
would also show a log normal distribution.
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Sandstone Reservoir
98959080502052 101
10
100
PROBABILITY (%)
P R O D U C T I V I
T Y
I N D E X
( B O P D / P S I )
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Log-normal Distribution of
Horizontal Well Productivities
98959080502052 100.1
1
Probabili ty (%)
P R O
D U C T I V I T Y
I N D E X
( B O P D / p s
i )
Sandstone Reservoir
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Reasons for Failure
Mechanical
Casing collapse, well collapse
Sanding & bridging of liner
Hole collapse after well stimulation
Difficulty in installing liner especially inmultilateral wells
Highly ‘sinusoidal’ well shape
Wrong well trajectory: drilling in unproductivezone, drilling in the water zone etc.
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Reasons for failure
Mechanical, continued
Pressure drop from toe to heel of a horizontal well
Difficulty in fracture initiation
Screen out of fractures
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Pressure Drop in aHorizontal Well
%10:Desirable Dpipe
pp
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Senlac/Winter Cummings/Dina
Pool, Canada
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Reasons for Failure
Geological /Reservoir
Formation damage: production from a horizontal
well is less than the nearby vertical wells
Reservoir heterogeneity (Producing length shorterthan the drilled length)
Economic failures
Low product prices
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CO2 WAG
HorizontalInjection Wells
South Cowden Unit,
Texas
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Gamma Ray - tool or other lithological toolson MWD assembly
Lithological logging
Production logging
•slotted liner completion (?)
Estimate from well test
Mud log
Measurement of Length
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Well Rate and
Producing Length
Double the producing length of a well and theproduction rate will increase by a factor of 1.44
Reduce producing well length by a factor of 4
and production rate will decrease by a factor of 2
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Permeability Ratio, kv/kh
Core data
kv/kh is generally an estimate
Geological literature for median length of
shale barriers
offshore bars (10 met long)
deltaic environment (400 met long)
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Continuity of Shale Intercalations as a
Function of Depositional Environment
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Reserves
Horizontal well reserves?Horizontal well flow
Initially transient flow
Once well encounters boundaries
Decline ( Steady State or Pseudo steady state Flow)
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660’
L
2000’
1320’
2xeh = 3,3202xev
2yev
1320’
2yeh
Vertical Well
Drainage Area = 40
Acres
xev/yev = 1
Horizontal Well
Drainage Area = 100
Acres
xeh/yeh = 2.5
Reservoir with Uniform HorizontalPermeability (ky/kx = 1)
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Anisotropic Reservoirs
If we drill a horizontal well along the low
permeability direction (perpendicular to the high
permeability direction) then the horizontal well
drainage area will be significantly larger than theconventional well drainage area.
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4174’
209’417’
2xev 2xeh=2417’
2yev
L=2000’
ky/kx = 100
Vertical Well
40 Acre Drainage Area
xe/ye = 0.1
Horizontal Well
232 Acre Drainage Area
xe/ye = 0.58
2yeh
Drainage Area
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Producing Characteristics & Recovery
for Vertical and Horizontal wellsin Austin Chalk, Niobrara and Bakken formations
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Review the Field Results
Reserves are difficult to estimate if wells are
(initial flow period) in transient flow.
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Single Phase Flow
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Type Curve for a Horizontal Well in the
Center of a Square Drainage Area
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Bakken Shale Example
5000’ Horizontal Well
8 Fracs
7744 psia Reservoir Pressure at 10780’
42’ Pay
8% Porosity
0.08 – 0.006 md Permeability
640 acre drainage area
14 years to Pseudo-steady state with 0.08 md !
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Bakken Shale Example
Exponential DeclineBakken Shale Exam ple Expon ential Decline
1
10
100
1,000
0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000Cumlative Oil, stb
O i l R
a t e ,
s t b / d
Data
Decline Fit
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Bakken Shale ExampleBakken Shale Exam ple Decline
1
10
100
1,000
1,000 10,000 100,000 1,000,000
Cumlative Production, stb
O i l R
a t e ,
s t
b / d
Data
Decline Fit
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Bakken Shale ExampleBakken Shale Exam ple Decline
1
10
100
1,000
10 100 1000 10000
Time, days
O i l R
a t e , s
t b / d
Data
Decline Fit
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Bakken History MatchBakken Shale Exam ple
0
100
200
300
400
500
600
700
800
0 50 100 150 200 250 300
Time, days
O i l R
a t e , s
t b / d
Data
8 Fractures 80'
4 Fractures 200'
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What We Know
1. Production rate
2. Drilled length
3. Number of fracture jobs
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What We Do Not Know
1. Producing well length2. kv/kh, Ratio of vertical & horizontal
permeability
3. Number of producing fractures
4. Effective fracture conductivity
5. Reserves in the transient flow period
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Conclusions
Horizontal well analysis requires engineering
judgment
It is difficult to get unique answer
Reserves are difficult to estimate during the
transient flow.