Low-Permeability Black Oil/Gas Condensate Reservoirs Using - - PowerPoint PPT Presentation
Low-Permeability Black Oil/Gas Condensate Reservoirs Using - - PowerPoint PPT Presentation
Analysis of Short-term (Flowback) and Long-term (Online) Production Data from Low-Permeability Black Oil/Gas Condensate Reservoirs Using Analytical/Semi-Analytical Methods C.R. Clarkson University of Calgary Outline Introduction A
Outline
Slide 2
Introduction
- A few facts
- Problem statement and objectives
Methods
- Modification of pseudovariables
- Iterative integral
- Dynamic drainage area
Special Application of RTA Methods:
- Fracture Height Estimation
Future Work Conclusions
Introduction
Slide 3
1000 m+ Horizontal Well Perforations Induced Hydraulic Fracture Network Extent of Contacted Reservoir Area
Fact:
- When producing from MFHWs completed in ultra-low permeability
reservoirs:
- a complex series of processes occurring at multiple scales are
initiated that we don’t completely understand
From: Clarkson et al. (JNGSE, 2016)
Introduction
Slide 4
Fact:
- When producing from MFHWs completed in ultra-low permeability
reservoirs:
- a complex series of processes occurring at multiple scales are
initiated that we don’t completely understand
meters Reactivated Natural Fractures Induced Hydraulic Fracture centimeters Natural Fracture Matrix millimeters Matrix with fine-scale laminations and fractures
A
0.5 mm STYLIOLINAmicrometers Matrix with interspersed organic and inorganic matter nanometers Nanopore structure
- f organic and
inorganic matter
From: Clarkson et al. (JNGSE, 2016)
Introduction
Slide 5
Fact:
- Reservoir characterization methods that account for the appropriate
physics are in their infancy
- Understanding how to advance characterization methods is
critical for sustainable development through primary and enhanced recovery processes
Multi-Phase Flow
Pressure Distance from hydraulic fracture Gas phase Condensate phase Hydraulic fracture pi pd pw Zone A B C?
Pore Confinement Effects
Free gas Adsorbed gas
Velocity ≠ 0
Complex Fracturing
etc.
Introduction
Slide 6
Reservoir and Hydraulic Fracture Characterization:
Reservoir Sample Analysis
km, kf, So, Sg, Sw, kro, krg, krw, ρm, ρb, øm, PSD, PTD, Pc, a, m, n, OM, IOM, Ro, Gc, Es, νs
Development Stage Pre-Drill Pre-Frac Frac Treatment Drill/Post-Drill Post-Frac Long-Term (Online) Production Analysis Type Properties Derived Seismic, 2D, 3D Analysis Category Reservoir and Hydraulic Fracture Characterization Log Analysis
km, kf, h, So, Sg, Sw, ρb, øm, øf, PSD, OM, IOM, ED, νD
Pre-Frac Welltest (DFIT)
khsys, Pclosure , Preservoir
Frac Monitoring (Microseismic) Flowback Analysis Frac Modeling Post-Frac Welltest (F/BU) Production Analysis
Frac geometry, SRV khf , khsys, Pbreakthrough, xf khsys, OGIP/OOIP , CGIP/COIP , xf, Ac, FcD khsys, xf, Ac, FcD xf, Ac, FcD
From: Clarkson et al. (JNGSE, 2016)
Introduction
Slide 7
RTA – Flowback/Online:
From SPE 166279
Introduction
Slide 8
RTA – Flowback/Online:
From: Clarkson et al. (TLE, 2014)
Flow Period Illustration of Flow Periods Flow-Regimes
X-Section View Plan View
Flowback: Depletion (Fracture) Before Breakthrough
- f Formation Fluids
(single-phase flow in fracture) Flowback: Transitional After Breakthrough
- f Formation Fluids
(multi-phase flow in fracture, single or multi-phase flow in formation) Long-Term Production: Linear Flow Formation Fluid Production Dominant (multi-phase flow in fracture, multi-phase flow in formation)
Flow-Period Illustration of Flow-Periods Flow-Regimes
X-Section View Plan View
Flowback: Depletion (Fracture) Before Breakthrough
- f Formation Fluids
(single-phase flow in fracture) Flowback: Transitional After Breakthrough
- f Formation Fluids
(multi-phase flow in fracture, single or multi-phase flow in formation) Long-Term Production: Linear Flow Formation Fluid Production Dominant (multi-phase flow in fracture, multi-phase flow in formation) ASSESS DATA VIABILITY
Review Production Data Review Well History Gather Reservoir, Completion and PVT Data
CHECK FOR DATA CORRELATION PRELIMINARY DIAGNOSIS
Filter Data for Clarity Review/Edit Data
IDENTIFY FLOW REGIMES PERFORM STRAIGHT- LINE ANALYSIS
Obtain Preliminary Estimate of Hydraulic Fracture Properties Obtain Preliminary Estimate of Reservoir Permeability Obtain Preliminary Estimate of Hydrocarbons-in-Place
PERFORM TYPE-CURVE ANALYSIS
Validate Hydraulic Fracture Property Estimates Validate Reservoir Permeability Estimate Validate Hydrocarbons- in-Place Estimate
PERFORM FORECAST WITH MODEL FIT EMPIRICAL MODEL TO FORECAST
STEP 1: STEP 2: STEP 3: STEP 4: STEP 5: STEP 6: STEP 7: STEP 8:
Introduction
Slide 9
Problem Statement:
- Analytical solutions used in RTA commonly assume:
- Single-phase flow of liquids
- Static reservoir and fracture properties
- Darcy’s Law is valid
- Constant rate or pressure production
- …..
Introduction
Slide 10
Objectives:
- Develop approaches that account for:
- Multi-phase flow
- Stress-dependent fracture and matrix properties
- Pore confinement effects: non-Darcy flow
- Pore confinement effects: fluid properties
2 4 6 8 10 12 14 10 20 30 40 50
Unpropped Fracture Gas (N2) Permeability (D) Effective Stress (MPa)
Mean Pore Pressure = 0.19 MPa Mean Pore Pressure = 0.53 MPa Mean Pore Pressure = 0.88 MPa Mean Pore Pressure = 1.23 MPa
Pore Confinement Effects
Free gas Adsorbed gas
Velocity ≠ 0
5 10 15 20 25 30 35 40 45 50
- 150
- 100
- 50
50 100 150 200 250 300 350 400
Pressure (MPa) Temperature (oC)
Phase Envelope of a Gas-Condensate Fluid Under Confinement
pore width = 300 nm pore width = 10 nm pore width = 5 nm pore width = 2 nm
“Dewpoint Suppression”
Methods
Slide 11
Multiple Approaches to Account for Non-Linearities:
- Modification of pseudovariables
- Iterative integral method
- Dynamic drainage area
Methods: Modification of Pseudos
Slide 12
1.Linearization Technique
- Linearization of governing PDE
- Using Pseudovariables
2.Method of Calculation
- Pseudovariables calculations
- Saturation pressure relationship
3.Backward Modeling
- Liquid solution
- Validation
Image Courtesy of Hamid Behmanesh
Methods: Modification of Pseudos
Slide 13
Images Courtesy of Hamid Behmanesh
Pseudopressure Pseudotime Liquid Solution Analogy!
- Calculation procedure: model inversion - linear flow analysis
(2P flow – JNGSE 2015, SPE 172928)
- Linearization
Methods: Modification of Pseudos
Slide 14
- Calculation procedure: model inversion - linear flow analysis
(2P flow – JNGSE 2015, SPE 172928)
- Pseudovariable Calculations:
(1) (2) (3) p PVT So (4) (5) pp
Image Courtesy of Hamid Behmanesh
a
Slide 15
Image Courtesy of Hamid Behmanesh
ta
t
(1) (2) (5) (6) (7)
p
(3) (4) p
Ginv. Material Balance Ginv. Np Gp
Methods: Modification of Pseudos
- Pseudovariable Calculations:
- Calculation procedure: model inversion - linear flow analysis
(2P flow – JNGSE 2015, SPE 172928)
Methods: Modification of Pseudos
Slide 16
Images Courtesy of Hamid Behmanesh
- Calculation procedure: model inversion - linear flow analysis
(2P flow – JNGSE 2015, SPE 172928)
- Inverse Modeling
- Infinite-acting linear flow solution - CP
Methods: Modification of Pseudos
Slide 17
- Application: model inversion - linear flow analysis (2P flow –
JNGSE 2015, SPE 172928)
1200 2400 3600 4800 1 10 100 1000 10000 100 200 300 400 500 Flowing Bottomhole Pressure, psia
Gas Rate (Mscf/D), Oil, Water Rate (STBdD)
Time, days Oil Rate Gas Rate Water Rate pwf
10 20 30 40 50 60 100 200 300 400 500 CGR and WGR, STB/MMscf Time, days Condensate Gas Ratio Water Gas Ratio
Constant CGR
- MFHW, tight (lean) gas condensate reservoir
Methods: Modification of Pseudos
Slide 18
- Application: model inversion - linear flow analysis (2P flow –
JNGSE 2015, SPE 172928)
1/qgas, 1/(qoil) versus √t
mCP
xf√k
Initial Properties
p
Distance of Investigation Material Balance
fCP
Cartesian coordinates
0.0 0.5 1.0 1.5 2.0 5 10 15 20
Inverse of Gas Rate, 1/(MMscf/D) Square Root of Time, days0.5
xf√k* = 21.5 ft.md0.5
- MFHW, tight (lean) gas condensate reservoir
Method: Iterative Integral
Slide 19
- Calculation procedure: model inversion - linear flow
analysis (2P flow – JNGSE 2013; 2016 and SPE 167176)
Image Courtesy of Farhad Qanbari
- Integrate non-linearities over the domain
t m q p f p m
CP
- w
c w
) ( ) (
1 1
) ( ) ( 1 :
D D D D c
dm m m g f
0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1000 2000 3000 4000 fc pw(psi) Bubble point pressure dSo/dp = 2 10-4 psi-1 dSo/dp = 1.75 10-4 psi-1 dSo/dp = 1.5 10-4 psi-1 (c)
. ˆ )) ( ( 2 exp ˆ )) ( ( 2 exp 1
ˆ ˆ
d d erfc m d d erfc m g m
D D D D D
) ( : guess Initial erfc mD
Method: Iterative Integral
Slide 20
- Calculation procedure: model inversion - linear flow
analysis (2P flow – JNGSE 2013; 2016 and SPE 167176)
Image Courtesy of Farhad Qanbari
Pressure Distance from hydraulic fracture Gas phase Condensate phase Hydraulic fracture pi pd pw Zone A B C?
Method: Iterative Integral
Slide 21
- Application: model inversion - linear flow analysis (2P flow
– JNGSE 2013; 2016 and SPE 167176)
- Example 1: MFHW, tight (rich) gas condensate reservoir
2000 4000 6000 8000 10000 12000 14000 5 10 15 20 25 30 (∆m)1P/qg/fc1P; (∆m)2P/qg/fc2P; (∆m)3P/qg/fc3P 106 psi2/cp/MMscf Gas linear superposition time (√day) Single-phase gas Two-phase gas+condensate Three-phase gas+condensate+water Three phase + stress-sensitivity (Ac√k)2P = 1.3 (Ac√k)1P (Ac√k)3P = 1.5 (Ac√k)1P Correction for condensate dropout Correction for water Correction for stress- sensitivity of permeability
Clarkson et al. (JNGSE, 2016)
Method: Iterative Integral
Slide 22
- Calculation procedure: model inversion - linear flow
analysis (2P flow – JNGSE 2013; 2016 and SPE 167176)
Image Courtesy of Farhad Qanbari
Pressure Distance from hydraulic fracture Oil phase Gas phase Hydraulic fracture pi pb pw Zone A B C
Method: Iterative Integral
Slide 23
- Application: model inversion - linear flow analysis (2P flow
– JNGSE 2013; 2016 and SPE 167176)
- Example 2: MFHW, tight oil reservoir
10 20 30 40 50 60 70 5 10 15 20 25 30 35 40 45 50 Δp/qo, (Δmo)/qo/fc2P; (Δmo)/qo/fc3P Oil linear superposition time (√day) Single-phase oil Two-phase oil+gas Three-phase oil+gas+water (Ac√k)O+G = 0.97 (Ac√k)O (Ac√k)O+G+W = 2.67 (Ac√k)O
Image Courtesy of Farhad Qanbari
Method: Iterative Integral
- Calculation procedure: model inversion - linear flow analysis
(Pore confinement – SPE 171357 and 180264)
1
) ( ] )[ ( ) ( 1 ˆ ) ˆ ( ) ˆ ( ) ˆ ( ) ( ) ( ) (
D D d r g D D c p p g g CP g c w i
d k c c c f p d p B p p k p t m q f p p
Bulk w i c ti gi ai i Confined w i c ti gi ai i Bulk f Confined f
p p f c k Z p p f c k Z x x ) ( ) ( ) ( ) (
Stress sensitivity and adsorption layer Changes in gas critical properties Desorption
Square-root-time plot
Slide 24
Clarkson et al. (JNGSE, 2016)
500 1000 1500 2000 2500 3000
- 200
- 100
100 200 300 Pressure, psia Temperature, oF 2-Phase boundary 2-Phase boundary confined Reservoir pressure path Critical point Critical point 0.5 1 1.5 2 2.5 3 2000 4000 6000 8000 10000 z-factor Pressure, psia z bulk z confined 0.0025 0.0035 0.0045 0.0055 0.0065 0.0075 0.0085 0.0095 2000 4000 6000 8000 10000 Bg, bbl/scf Pressure, psia Bg bulk Bg confined 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 2000 4000 6000 8000 10000 µ, cp Pressure, psia µ bulk µ confined
Method: Dynamic Drainage Area
Slide 25
- Calculation procedure: model inversion - linear flow analysis
(2P flow – SPE 180230)
1 inv ,
- S
1 inv
p
Hydraulic Fracture
yinv1
ye1
yinv2
2 inv ,
- S
2 inv
p
Method: Dynamic Drainage Area
Slide 26
Slide Courtesy of Farhad Qanbari
ti gi i i c inv D inv tD inv D inv gD g wf g inv g
c t k A T p k p c p p q p m p m 56 . 576 ) ( ) ( ) ( ) ( ) ( ) (
) ( 615 . 5 ) ( ) ( ) ( ) ( 615 . 5 1000 4
, , inv
- inv
- inv
inv s inv gd inv g inv
- i
- i
i si gdi gi i inv ft p
p B S p p R p B S p B S R B S h y x G
ti i i i inv
c t k y
- Calculation procedure: model inversion - linear flow analysis
(2P flow – SPE 180230)
- An approximate semi-analytical/empirical method
- Uses boundary-dominated solution for transient flow
Method: Dynamic Drainage Area
Slide 27
- Calculation procedure: model inversion - linear flow analysis
(2P flow – SPE 180230)
Slide Courtesy of Farhad Qanbari
- An iterative process
- Time instead of superposition time
- Average pressure instead of initial pressure
- Coefficient of linear flow equation is different
A√k
t q p m p m
g wf g inv g
) ( ) (
f (A√k)
Method: Dynamic Drainage Area
Slide 28
SPE 180230
- Application: model inversion - linear flow analysis (2P flow –
SPE 180230)
- Example 1: MFHW, wet gas reservoir (CGR=20 STB/MMscf)
500 1000 1500 2000 2500 3000 500 1000 1500 2000 2500 3000 200 400 600 800 1000 1200 pwf (psia) qg (Mscf/Day) Time (days) Gas Rate - Field Fata Flowing Bottomhole Pressure
(a)
Method: Dynamic Drainage Area
Slide 29
- Application: model inversion - linear flow analysis (2P flow –
SPE 180230)
- Numerical history-match and DDA-corrected linear flow plot
1000 2000 3000 4000 5000 10 20 30 DDA-Corrected Gas RNP (psi2/cp/scD) √Time (√day) 500 1000 1500 2000 2500 3000 500 1000 Gas Rate (Mscf/Day) Time (days) Gas Rate - Field Fata Gas Rate - Numerical Simulation
Parameter RC1 Total Ac√ki – numerical simulation 8200 Total Ac√ki – DDA-corrected linear flow plot 7400 (10%)
Method: Dynamic Drainage Area
Slide 30
SPE 180230
- Application: model inversion - linear flow analysis (2P flow –
SPE 180230)
- Example 2: MFHW, gas condensate reservoir (CGR = 100
STB/MMscf)
500 1000 1500 2000 2500 3000 500 1000 1500 2000 2500 3000 100 200 300 400 pwf (psia) Gas Rate (Mscf/Day) Time (days) Gas Rate - Field Fata Flowing Bottomhole Pressure
(a)
100 200 300 400 500 100 200 300 400 Condensate Rate (STB/Day) Time (days)
Method: Dynamic Drainage Area
Slide 31
SPE 180230
- Application: model inversion - linear flow analysis (2P flow –
SPE 180230)
- Numerical history-match
500 1000 1500 2000 2500 3000 500 1000 1500 2000 2500 3000 100 200 300 400 Well Bottomhole Pressre (psia) Gas Rate (Mscf/Day) Time (days) Gas Rate - Field Fata Gas Rate - Numerical Simulation
(a)
100 200 300 400 500 100 200 300 400 Condensate Rate (STB/Day) Time (days) Condensate Rate - Field Fata Condensate Rate - Numerical Simulation
(a)
Method: Dynamic Drainage Area
Slide 32
- Application: model inversion - linear flow analysis (2P flow –
SPE 180230)
- DDA-corrected gas linear flow plot
100 200 300 400 500 10 20 DDA-Corrected Gas RNP (psi2/cp/scfD) √Time (√day)
Parameter RC2 Total Ac√ki from numerical simulation 23500 Total Ac√ki from DDA-corrected linear flow plot 26200 (12%)
Method: Dynamic Drainage Area
Slide 33
- Calculation procedure: long-term forecasting (2P flow –
SPE 175929)
1 inv ,
- S
1 inv
p
Hydraulic Fracture
yinv1
ye1
yinv2
2 inv ,
- S
2 inv
p
Method: Dynamic Drainage Area
Slide 34
- Calculation procedure: long-term forecasting (2P flow –
SPE 175929)
ft inv wf g inv g i wf v ft inv
- i
- i
wf
- inv
- i
- x
y T p m p m h k p R x y B p m p m h k q 2 1424 ) ( ) ( 1000 ) ( 2 2 . 141 ) ( ) (
) p ( B S ) p ( ) p ( R ) p ( B . S ) p ( B S R B . S h y x t q N
inv gd inv , g inv inv v inv
- inv
,
- inv
gdi gi i vi
- i
- i
i inv ft
- p
6 6
10 615 5 10 615 5 4
- + analogous equations for gas…
- Pseudopressure calculations require S-P relationships – used
empirical approach
Method: Dynamic Drainage Area
Slide 35
- Application: long-term forecasting (2P flow – SPE 175929)
- MFHW, tight gas condensate reservoir
2000 4000 6000 8000 10000 12000 14000 16000 18000 200 400 600 800 1000 Gas Rate (Mscf/d), BHP (psia) Time (day) Gas Rate - Field Data BHP Gas Rate - DDA 500 1000 1500 2000 2500 3000 3500 4000 200 400 600 800 1000 Cumulative Gas (MMscf) Time (day) Gas Rate - Field Data Gas Rate - DDA 200 400 600 800 1000 1200 1400 1600 1800 2000 200 400 600 800 1000 Condensate Rate (STB/d) Time (day) Condensate Rate - Field Data Condensate Rate - DDA 20 40 60 80 100 120 140 160 180 200 200 400 600 800 1000 Cumulative Condensate (MSTB/d) Time (day) Condensate Rate - Field Data Condensate Rate - DDA
Slide Courtesy of Farhad Qanbari
Method: Dynamic Drainage Area
Slide 36
- Calculation procedure: flowback forecasting (2P flow – URTeC
2460083)
Flow Period Illustration of Flow Periods Flow-Regimes
X-Section View Plan View
Flowback: Depletion (Fracture) Before Breakthrough
- f Formation Fluids
(single-phase flow in fracture) Flowback: Transitional After Breakthrough
- f Formation Fluids
(multi-phase flow in fracture, single or multi-phase flow in formation)
Flow-Period Illustration of Flow-Periods Flow-Regimes
X-Section View Plan View
Flowback: transient/depletion Before Breakthrough
- f Formation Fluids
(single-phase flow in fracture) Flowback/Early Production: transitional/linear Breakthrough
- f Formation Fluids
(multi-phase flow in fracture, single or multi-phase flow in formation)
Element of symmetry yinv1 wf ye xf Swi,m Soi,m pi,m Swi,f Soi,f pi,f (Sw,inv,f)1 (So,inv,f)1 (pav,inv,f)1 (Sw,inv,m)1 (So,inv,m)1 (pav,inv,m)1 (Sw,inv,f)2 (So,inv,f)2 (pav,inv,f)2 (Sw,inv,m)2 (So,inv,m)2 (pav,inv,m)2 yinv2 xinv1
Source: Clarkson et al. (URTeC 2016)
Method: Dynamic Drainage Area
Slide 37
- Application: flowback forecasting (2P flow – URTeC 2460083)
- MFHW, tight oil reservoir
2000 4000 6000 8000 10000 0.1 1 10 100 1000 10000 2 4 6 8 10 12
Pwf (psia) and GOR (SCF/STB) Gas (Mscf/D), Water and Oil (STB/D) Rate
Time, days
Fluid Production Rates
Water Rate Oil Rate Gas Rate Pwf GOR
From Clarkson et al. (TLE, 2014)
Method: Dynamic Drainage Area
Slide 38
- Application: flowback forecasting (2P flow – URTeC 2460083)
- MFHW, tight oil reservoir
100 200 300 400 500 600 2 4 6 8 10 qo (STB/day) Time (day) Oil rate - field data Oil rate - DDA
a)
0.2 0.4 0.6 0.8 1 1.2 2 4 6 8 10 Np (MSTB) Time (day) Cumulative oil - field data Cumulative oil - DDA
b)
100 200 300 400 500 600 2 4 6 8 10 qg (Mscf/day) Time (day) Gas rate - field data Gas rate - DDA
a)
0.2 0.4 0.6 0.8 1 1.2 2 4 6 8 10 Gp (MMscf) Time (day) Cumulative gas - field data Cumulative gas - DDA
b)
500 1000 1500 2000 2500 3000 2 4 6 8 10 qw (STB/day) Time (day) Water rate - field data Water rate - DDA
a)
1 2 3 4 5 6 7 8 2 4 6 8 10 Wp (MSTB) Time (day) Cumulative water - field data Cumulative water - DDA
b)
Special Application: Fracture Height
Slide 39
Concept
With known initial compositions of two layers (target and bounding), it is possible to estimate penetration height ratio (h1/h2) based on the short-term flow rate and composition of the production stream
Impermeable Layer
Source: Ghaderi and Clarkson (JNGSE, in press)
Special Application: Fracture Height
Slide 40 Source: Ghaderi and Clarkson (JNGSE, in press)
- Calculation procedure:
- Writing material balance for each individual component, it can be
concluded that:
It is important to find a proper average pressure to evaluate these properties for each layer with different composition
Special Application: Fracture Height
Slide 41 Source: Ghaderi and Clarkson (JNGSE, in press)
- Calculation procedure:
Behmanesh (2014) proposed the following relationship for average pressure: It is possible to show that the above equation is equivalent to: If we make the equation more general we can it use more efficiently:
Special Application: Fracture Height
Slide 42 Source: Ghaderi and Clarkson (JNGSE, in press)
- Comparison with numerical simulation:
82.00 82.20 82.40 82.60 82.80 83.00 83.20 83.40 83.60 83.80 84.00 5 10 15 20 25
η, mole percentage Time, day
- Config. I
- Config. II
82.00 82.20 82.40 82.60 82.80 83.00 83.20 83.40 83.60 83.80 84.00 5 10 15 20 25
η, mole percentage Time, day
- Config. III
- Config. IV
y = 1.0017x - 0.0008 R² = 0.9924 2 4 6 8 10 12 2 4 6 8 10 12 h2/h1 (Analytical) h2/h1 (Simulation)
τ = 0.80
Future Work
Slide 43
Continue development
- f
multi-phase RTA analysis, including improvement of our previous work on boundary- dominated flow (FMB; SPE 169515) Incorporation of fluid chemistry (e.g. salinity) into the analysis Extension of methods to account for inter-well/stage communication Application of fracture height-growth method to field data
Conclusions
Slide 44
Conventional RTA methods use simplified solutions that do not capture the physics of flow and storage in unconventional reservoirs Our research group have applied 3 different approaches (pseudovariables, interative integral, dynamic drainage area) to account for unconventional reservoir complexities These approaches have been successfully applied to extract reservoir and hydraulic fracture information from multi-fractured horizontal wells producing from tight
- il/gas condensate reservoirs
Acknowledgements
Slide 45