reservoir problems

Reservoir Mechanisms and Problem types

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


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


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


Five Spot Pattern


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%


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 a

t br e

akth

roug

h


Aerial Sweep Problems

Original oil water contact

Proposed injector

Proposed oil producers


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


Homogeneous zone

InjectorProducerProducer


Discontinuous ZonesInjectorInjectorInjector Producer Producer


Sandstone Geology

Vertical stacking Isolated stackingLateral stacking


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

Dep

th, f

t


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


Favorable Permeability Profile

Injector

Producer

Oil

Sea level

Depos

ition

Fine

Coarse

Incr

easi

n g

ener

gy

Gamma Perm


Unfavorable Permeability Profile

Gamma Perm

Water level

Deposition

Coarse

Fine

Eros

ion

Injector

Producer

Oil


"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

t1t2t3t4


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

perm

eabi

lity

fra c

tion

Swi


Good WaterProduced with hydrocarbon

Cannot be shut-offwithout loosing hydrocarbon

What Are The Water Problem Types?

Simple Complex3 4 5 6 7 8 9 101 2


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


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 Flow02


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


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


Fissures to an Injector

Areal sweep problem Rapid breakthrough Test with tracers

Treat at injector Use flowing gel

05


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


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


Poor Areal Sweep Areal sweep

problem Heterogeneous Anisotropic Sand channel Fingering due to

mobility Treat at injector

Polymer flood Often not

economic

Aquifer08


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


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


Which Reservoir?

Reservoir Mechanisms and Problem typesReservoir Problem typesDisplacement efficiency Areal sweep efficiencyFive Spot PatternEffect of Mobility RatioAreal Sweep EfficiencyAerial Sweep ProblemsVertical sweep efficiencyHomogeneous zoneDiscontinuous ZonesSandstone GeologyPermeability Profile BrentRFT PressuresFavorable Permeability ProfileUnfavorable Permeability Profile"Good" WaterRelative PermeabilityWhat Are The Water Problem Types?Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Which Reservoir?

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