02 Reservoir Problems
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Transcript of 02 Reservoir Problems
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Reservoir Mechanisms and Problem types
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2 WC Reservoir and Problems14-Jun-02
Reservoir Problem types
• Reservoir water flow mechanisms– Displacement efficiency– Vertical sweep efficiency– Areal sweep efficiency
• “Good” water, “Bad” water
• Problem types
• Well and facilities
• Scale
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3 WC Reservoir and Problems14-Jun-02
Displacement efficiency
• Fraction of oil displaced from rock swept with water
• Oil available = (1 - Sor - Swi)
• Total oil = (1- Swi)• Not target for water control• Sor can be changed by
surfactant flood Swi
Sor
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4 WC Reservoir and Problems14-Jun-02
Areal sweep efficiency
• Fraction of horizontal section swept by water
• Dependent on– Areal permeability
distribution– Permeability anisotropy– Deposition environment– Flood pattern– Fluid mobility
• Limited target for water control
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5 WC Reservoir and Problems14-Jun-02
Five Spot Pattern
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6 WC Reservoir and Problems14-Jun-02
Effect of Mobility Ratio
M=0.4
Breakthrough
83%
WOR = 0.6
87%
WOR = 4.7
96%
M=1.4
Breakthrough
65%
WOR = 0.5
70%
WOR = 2
82%
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Areal Sweep Efficiency
0.1 0.2 0.3 0.5 1 2 3 5 100.5
0.6
0.7
0.8
0.9
1
Mobility Ratio
Ea
at
bre
akth
rou
gh
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Aerial Sweep Problems
Original oil water contact
Proposed injector
Proposed oil producers
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Vertical sweep efficiency
• Fraction of vertical section swept by water
• Dependent on– Vertical permeability profile– Permeability contrast– Deposition environment– Gravity segregation– Fluid mobility
• Prime target for water control
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Homogeneous zone
InjectorProducerProducer
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Discontinuous Zones
InjectorInjectorInjector Producer Producer
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12 WC Reservoir and Problems14-Jun-02
Sandstone Geology
Vertical stacking Isolated stackingLateral stacking
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Permeability Profile Brent
0 2 4 6 8 10 12(9,700)
(9,600)
(9,500)
(9,400)
(9,300)
(9,200)
(9,100)
(9,000)
Permeability, Darcies
De
pth
, ft
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14 WC Reservoir and Problems14-Jun-02
RFT Pressures
5,2005,400
5,6005,800
6,0006,200
6,400(9,700)
(9,600)
(9,500)
(9,400)
(9,300)
(9,200)
(9,100)
(9,000)
Pressure, psi
Dep
th, f
t
Initial reservoir pressure
Upper Jurassic
Rannoch
Etive
NessTarbut
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Favorable Permeability Profile
Injector
Producer
Oil
Sea level
Deposition
Fine
Coarse
Incr
easi
ng
ener
gy
Gamma Perm
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Unfavorable Permeability Profile
Gamma Perm
Water level
Deposition
Coarse
Fine
Ero
sion
Injector
Producer
Oil
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"Good" Water• Needs to be produced with oil• Cannot be shut-off without shutting off oil
• Down-hole separation may be a solution
Injector Producer
t1
t2
t3
t4
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Relative Permeability
0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
Water saturation, fraction pore space
rela
tive
per
mea
bili
ty f
ract
ion
Swi
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Good WaterProduced with hydrocarbon
Cannot be shut-offwithout loosing hydrocarbon
What Are The Water Problem Types?
Simple Complex
3 4 5 6 7 8 9 101 2
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20 WC Reservoir and Problems14-Jun-02
Tubing / Casing / Packer Leak
Leak in the wellbore
– Detect with spinner or temperature log
Solution case specific
– Shut-off fluids Leak Matrix
– Mechanical shut-off
01
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21 WC Reservoir and Problems14-Jun-02
Problem in or near wellbore
– Poor cement
– Cave due to sanding
– Channel in formation
Solution is case specific
– Cement in channel
– Gel in formation
– Resin
Near-Wellbore Flow
02
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22 WC Reservoir and Problems14-Jun-02
OWC moving up Bottom water uniform
sweep
– OWC move up slowly
– Low vertical permeability
Solution
– Abandon perforations from the bottom Bridge plug
(through tubing) Cement plug
03
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23 WC Reservoir and Problems14-Jun-02
High Perm. Layer - No Crossflow Vertical sweep
problem
Edge water
– Water flood or aquifer
– Thief layer
– High perm streak
Shut off layer
– Producer or Injector
– Mechanical or fluid
04
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24 WC Reservoir and Problems14-Jun-02
Fissures to an Injector
Areal sweep problem
– Rapid breakthrough
– Test with tracers
Treat at injector
– Use ‘flowing gel’
05
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25 WC Reservoir and Problems14-Jun-02
Fissures to a Water Layer Oil bypassed
– Natural fissures
– Hydraulic fracture
– Fault
– Water flow in fissures
– Oil in matrix
Treat producer
– Flowing gel
– Over displace
06
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26 WC Reservoir and Problems14-Jun-02
Water Coning Bottom water
– Near oil/water contact
Critical oil rate
– Depends on Kv
– Depends on gel radius
Laterals
Treat with layer of gel
– Near bottom perforations
– Large volumes required
– Long delay times
07
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27 WC Reservoir and Problems14-Jun-02
Poor Areal Sweep Areal sweep
problem
– Heterogeneous
– Anisotropic
– Sand channel
– Fingering due to mobility
Treat at injector
– Polymer flood
– Often not economic
Aquifer
08
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28 WC Reservoir and Problems14-Jun-02
Gravity Segregated Layer Vertical sweep
problem
Edge water
– Water flood or Aquifer
– One main zone
– High vertical permeability
– Local coning
Laterals
Modify profile
– Producer
09
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High Perm. Layer - with Crossflow Vertical sweep
problem
Edge water
– Water flood or aquifer
– Thief layer
– High perm streak
Shut off layer
– Deep gel penetration
– Difficult to place
– Often not economic
10
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30 WC Reservoir and Problems14-Jun-02
Which Reservoir?