Upload
tboxranger
View
2.093
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Discussion on Pore Geometry Observations in Carbonate Reservoirs
Citation preview
11
Pore Geometry Effects in Pore Geometry Effects in Carbonate ReservoirsCarbonate Reservoirs
22
Common Cretaceous Carbonate Rock Textures
Unlike sandstones, carbonate pore systems do not
generally exhibit a relationship between pore throat size and
pore body size.
The connectivity between pores in
carbonates is generally fairly
chaotic.
33
Pore Geometry Model
Hi K
Low K
PoreBody
Plug Scale
Pore Throat
PoreBodyPore
Body
PoreBody
PoreBody
t = o + e
44
Rock Type 1
•Largest pore throats•Well connected•Lowest Swi•Highest K•Intermediate porosity•Little or no microporosity
Rock Typing Pore Geometry
55
Back-ups?
Rock Type 3
•Strongly Bimodal -Large and small pore throats•Some macro pores connected via micropores•Higher Swi at a given H•Intermediate K•Intermediate to low porosity•Abundant microporosity within grains and matrix (where present)
Rock Typing Pore Geometry
66
Pressure @ 400 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
Pore Body SizePore Body Size
Throat Size Throat Size
Greater probability of
large pore bodies
77
Pressure @ 2 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
88
Pressure @ 5 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
Winland Rock Type
f(k/)
99
Pressure @ 10 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
1010
Pressure @ 20 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
1111
Pressure @ 40 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
1212
Pressure @ 60 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
Non Winland Behavior
1313
Pressure @ 80 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
1414
Pressure @ 100 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
1515
Pressure @ 200 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
1616
Pressure @ 400 psi
Sw>0.0 & <=0.2
Sw>0.2 & <=0.4
Sw>0.4 & <=0.6
Sw>0.6 & <=0.8
Sw>0.8 & <=1.0
K (
md)
Phi (%)
0.01
10000
0.1
1
10
100
1000
0 5 10 15 20 25 30
Significant volume of
poorly connected
porosity
1717
Hydrocarbon Habitat Hydrocarbon Habitat
Pc = 0
SwiTransition
Zone
60 to 90 psi
Oil in both efficient and occluded pore
volumesOil in efficient pore volume
only
t = o + e
1818
Impact of Efficient Porosity
Pore Geometry Effects
Total Porosity
Efficient Porosity•Logs & Core sense total porosity.
•Efficient porosity contains hydrocarbons at low buoyancy.
•Pores connected by efficient porosity predominately oil wet.
•Occluded pores water wet and charged only at high buoyancy.
EfficientOccluded
Efficient PhiTotal Phi
t = o + e
1919
Pore Geometry & Formation EvaluationWhat is your confidence on Sw?
m = 2.38
m = 1.75
a=1 m=2.03 n=1.98 Rw=0.018@FT
Uncertainties:•How to vary Archie exponents as a function of rock type (incorporate Sw from TDT?)
•Capillary Pressure variables ( cos )
•Pore Geometry effects upon wettability and water saturation
With confidence:•Connate water properties (Rw, water)
•Oil properties (oil)
•Pc=0
100
150
200
250
300
0% 20% 40% 60% 80% 100%Sw
He
igh
t A
bo
ve
Pc
=0
SW-OH
Sw-TDT
RT-1
RT-2
RT-3
RT-4
Sw
Aquifer Well
2020
Effects of AcidizationEffects of Acidization
Acid Effects on CH CNL
2121
Pore Geometry Model
Hi K
Low K
PoreBody
Plug Scale
Pore Throat
PoreBodyPore
Body
PoreBody
PoreBody
t = o + e
2222
Pore Geometry ModelPore Geometry Model
• Conductivity Equation – conductive matrix model
n
o
ne
e
oSwCw
SwCw
CtFF
n
w
mon
ew
me
o
oe
SwaR
SwaR
Ct
Efficient Efficient
2323
Conductive Matrix ModelConductive Matrix Model
Assumptions:
Swo = 100%
Swe = 20%
t = 25%
Pore Geometry Model
t = o+e
0.1
1
10
0% 10% 20% 30%
Efficient Porosity
Res
isti
vity
Rt
Ro
Ft = 25%
Rw =0.018
me =2.1
mo =1.7
n =2.0
2424
Conductive Matrix ModelConductive Matrix Model
Assumptions:
Swo = 100%
Swe = 20%
t = 25%
Pore Geometry Model
t = o+e
0.1
1
10
0% 10% 20% 30%
Efficient Porosity
Res
isti
vity
0%10%20%30%40%50%60%70%80%90%100%
Rt
Ro
Swt
2525
Pore Geometry ModelPore Geometry Model
Efficient filled low in
column
Multiple rock types with
similar degrees of Efficient
Occluded filling slowly with height
•Multiple Rock Types can exhibit the same type of Efficient , making them indistinguishable at low buoyancy pressures.
•The high conductivity of the Occluded dominates the resistivity measurement, especially at low column heights.
Occludedincreasing
2626
Questions & ConsiderationsQuestions & Considerations
DiscussionDiscussion
2727
Full Cycle Impact of Pore GeometryFull Cycle Impact of Pore Geometry
• Well Planning– The position of the target interval as a function of buoyancy is a
critical factor.• High in the column there is a greater probability that the oil is
charging the occluded pore systems.• Near Pc=0 only the large pore systems will contain oil.
– Near the contact low drawdown is necessary to prevent coning.• Horizontal wells that will have small drainage radii.• Consider using MRC wells to effectively increase drainage area.• Minimize porpoising. Sumps cut down the effective flowing cross
section, especially in low influx wells.• Strongly consider OBM drilling fluids combined with UBD and/or
CTD. Also pre-consider the deployment of ICDs.
2828
Full Cycle Impact of Pore GeometryFull Cycle Impact of Pore Geometry
• Drilling the well– Over balance drilling with non-wetting fluid introduces a relative perm dominated
skin which can be significant in low perm rock.– Over balance drilling conveys cuttings into the large pore system further reducing
to eliminating perm by reducing or blocking pore throats.– OBM allows you to easily detect if water is the mobile phase.
• Completions– Acid is conveyed as ions in water suspension and will only react if they come in
contact with the rock surface. Occluded pore volumes are connected by small pore throats and are most likely effected. Significant volumes of “trapped” water can be mobilized.
– Acidization dramatically alters the Kv/Kh in the near wellbore region.– Acid rinds in perforated completions can never be isolated by conventional
squeezes. The first continuous filament of water entering is conveyable through the entire continuous perforation length.
– If required in perforated production wells, consider short perforation intervals and numerous blanks to facilitate conformance at the well.
2929
Full Cycle Impact of Pore GeometryFull Cycle Impact of Pore Geometry
• Formation Evaluation– Computing total porosity is straight forward but what of efficient
porosity?– Do you trust your Sw computations?
• Archie exponents should be a function of RRT• Induction tools are conductivity seeking devices• Does the Archie Sw favorably match capillary response?• How do you measure drainage RI in oil wet rocks?• Is there a better way to obtain Sw using logs? Limitations?
– Do you understand your flow SCAL?• Which volume of porosity are you flowing through in the lab?• What would your Rel-k curves look like if the occluded pore volume was
eliminated (low buoyancy model)? • Is the hydrocarbon in the right pore geometry when you execute the test?• Do you do Deane-Stark on results to verify flood out ROS?• Have you made experiments that cover the entire column height range?
3030
Full Cycle Impact of Pore GeometryFull Cycle Impact of Pore Geometry
• Recovery Process– Do you understand the relative distributions of
hydrocarbons in the efficient and occluded pore geometries?
– At low sweep speeds, displacement should be more piston-like within the efficient pore system.
– Caution that water is often more mobile than the oil.– ROS will most probably be contained within the
occluded pore volume. The higher the column, the greater that volume.
• What mechanisms facilitate mobilizing hydrocarbons locked in occluded pore volumes?
3131
backupsbackups
3232
Heterogeneity at the Plug Level
Hi K
Low K
PoreBody
Plug Scale
Pore Throat
PoreBodyPore
Body
PoreBody
PoreBody
3333
Sample Preparation for RRTSample Preparation for RRT1 ½ x 3 inch host plug (Routine & SCAL)
1 inch RHC
P&P @ 800 psi
FF
Kbrine, miniperm
MICP
1 inch RHC
P&P @ 800 psi
Miniperm
TS
MICP spare
1 inch RHC
P&P @ 800 psi
Miniperm
TS spare
MICP spare
1 ½ inch RHC
P&P @ 800 psi
P&P @ elevated PSI
FF
Kbrine, miniperm