Compositional Grading Theory and Practice Lars Hier , Statoil Curtis - - PowerPoint PPT Presentation

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Compositional Grading Theory and Practice Lars Hier , Statoil Curtis - - PowerPoint PPT Presentation

Apr 06, 2023 190 likes •480 views

SPE 63085 Compositional Grading Theory and Practice Lars Hier , Statoil Curtis H. Whitson , NTNU and Pera Theory Simple 1D Gradient Models Isothermal Gravity/Chemical Equilibrium Defining General Characteristics Different

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SLIDE 1

SPE 63085

Compositional Grading Theory and Practice

Lars Høier, Statoil Curtis H. Whitson, NTNU and Pera

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SLIDE 2

“Theory”

Simple 1D Gradient Models

  • Non-Isothermal Models with Thermal Diffusion.

– Quantitative Comparisons

  • Different Models
  • Different Fluid Systems
  • Isothermal Gravity/Chemical Equilibrium

– Defining General Characteristics

  • Different Fluid Systems (SPE 28000)
  • Quantifying Variations
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SLIDE 3

“Practice”

  • Using Samples
  • Quantifying Uncertainties

… Develop a Consistent EOS Model

  • Defining Trends
  • Fluid Communication
  • Initializing Reservoir Models
  • Predicting a Gas-Oil Contact
  • History Matching
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SLIDE 4
  • Balance of chemical and gravity potentials
  • Given … { Href , pRref , Tref , ziref } … calculate

– zi(H) – pR(H) – psat(H)

  • IOIP(H) ~ zC7+(H)

Isothermal Gradient Model

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SLIDE 5

4500 4600 4700 4800 4900 5000 0.00 0.05 0.10 0.15 0.20 0.25 0.30

C7+, mole fraction Depth, m

400 425 450 475 500 525

Pressure, bara

Reference Sample Reservoir Pressure C7+ Saturation Pressure

Isothermal Gradient Model

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SLIDE 6

4500 4600 4700 4800 4900 5000 0% 5% 10% 15% 20% 25% 30%

C7+, mol-% Depth, m

400 425 450 475 500 525

Reference Sample GOC

STO Oil Added Using Gradient Calculation

IOIP(H) ~ zC7+(H)

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SLIDE 7
  • Component Net Flux = Zero

– Chemical Energy – Gravity – Thermal Diffusion ???

  • Given … { Href , pRref , Tref , ziref } … calculate

– zi(H) – pR(H) – psat(H)

Non-Isothermal Gradient Models

T(H)

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SLIDE 8

Non-Isothermal Gradients

Thermal Diffusion Models

  • Thermodynamic

– Haase – Kempers

  • Thermodynamic / Viscosity

– Dougherty-Drickhamer (Belery-da Silva) – Firoozabadi-Ghorayeb

  • “Passive”

– Thermal Diffusion = 0 , ∇T≠0

G T G T T G T

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SLIDE 9

Ekofisk Example

15 20 25 30

  • 10900
  • 10600
  • 10300
  • 10000
  • 9700
  • 9400

C7+ Mole Percent Depth, ft SSL

Isothermal GCE Haase Kempers Belery, da Silva (25%) Firoozabadi-Ghorayeb

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SLIDE 10

Cupiagua

4000 5000 6000 7000

  • 15000
  • 14000
  • 13000
  • 12000
  • 11000

Pressure, psia Depth, ft SSL

Reference Depth GOC Isothermal Model Field-Data Based Initialization

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SLIDE 11

Cupiagua

0.2 0.4 0.6 0.8

  • 15000
  • 14000
  • 13000
  • 12000
  • 11000

IOIP / HCPV, (Sm 3 / m3) Depth, ft SSL

Reference Depth Isothermal Model Field-Data Based Initialization GOC

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SLIDE 12

Cupiagua

10 15 20 25 30 35

  • 15000
  • 14000
  • 13000
  • 12000
  • 11000

C7+ Mole Percent Depth, ft SSL

Reference Depth GOC Field-Data Based Initialization Isothermal Model

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SLIDE 13

Theory – Summary

  • Isothermal model gives maximum gradient
  • Convection tends to eliminate gradients
  • Non-isothermal models generally give a gradient

between these two extremes

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SLIDE 14

Complicating Factors

when traditional 1D models are inadequate

  • Thermally-induced convection
  • Stationary State not yet reached
  • Dynamic aquifer depletes light components
  • Asphaltene precipitation
  • Varying PNA distribution of C7+ components
  • Biodegredation
  • Regional methane concentration gradients
  • Multiple source rocks
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SLIDE 15

“Practice”

  • Using Samples
  • Quantifying Uncertainties

… Develop a Consistent EOS Model

  • Defining Trends
  • Fluid Communication
  • Initializing Reservoir Models
  • History Matching
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SLIDE 16
  • Plot C7+ mol-% versus depth
  • zC7+ ~ 1/Bo = OGR/Bgd

– i.e. IOIP=f(depth)

  • Use error bars for depth & composition

– ∆C7+ ≈ ∆OGR / (Co + ∆OGR)

Co=(M/ρ)7+ (psc/RTsc)

Using Samples Quantifying Uncertainty

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SLIDE 17

3800 4000 4200 4400 4600 4800 5000 5 10 15 20 25 30 35

C7+ Mole Percent True Vertical Depth, mSS

Well D Well E Well C Well A DST 1 Well B Well A DST 2

Åsgard, Smørbukk Field

Geologic Layer “A”

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SLIDE 18

Develop a Consistent EOS

  • Use All Available Samples with

– Reliable Compositions – Reliable PVT Data

  • Fit Key PVT and Compositional Data

– Reservoir Densities – Surface GORs, FVFs, STO Densities – CVD Gas C7+ Composition vs Pressure – Reservoir Equilibrium Phase Compositions

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SLIDE 19

Defining Trends

Use All Samples Available

  • Sample Exploration Wells

– Separator Samples – Bottomhole Samples – MDT Samples (water-based mud only)

  • Oil Samples may be Corrected
  • Gas Samples with Oil-Based Mud should not be used
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SLIDE 20

Defining Trends

Use All Samples Available

  • Production Wells

– “Early” Data not yet affected by

  • Significant Depletion
  • Gas Breakthrough
  • Fluid Displacement / Movement
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SLIDE 21

Defining Trends

  • Any sample's “value” in establishing a trend is

automatically defined by inclusion of the samples error bars in depth and composition.

  • Samples considered more insitu-representative

are given more "weight" in trend analysis.

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SLIDE 22

Fluid Communication

  • Compute isothermal gradient for each and every

sample

  • Overlay all samples with their predicted gradients

– Don’t expect complete consistency – Do the gradient predictions have similar shape ? – Do the gradient predictions cover similar range in C7+ ?

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SLIDE 23

3800 4000 4200 4400 4600 4800 5000 5 10 15 20 25 30 35

C7+ Mole Percent True Vertical Depth, mSS

Well D Well E Well C Well A DST 1 Well B Well A DST 2

Åsgard, Smørbukk Field

Geologic Layer “A”

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SLIDE 24

Orocual Field

Venezuela

12,000 13,000 14,000 15,000 16,000 5 10 15 20 25 C7+ Mole Percent Mid-Perforation Depth, ft SS ORS-65 ORC-25 ORS-54 ORS-54 ORS-56

Structurally High Wells

ORS-66

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SLIDE 25

Initializing Reservoir Models

  • Linear interpolation between “select” samples

– Guarantees Automatic “History Matching” – Check for consistent of psat vs depth

  • Extrapolation

– Sensitivity 1 : isothermal gradient of outermost samples – Sensitivity 2 : constant composition of outermost samples

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SLIDE 26

3800 4000 4200 4400 4600 4800 5000 5 10 15 20 25 30 35

C7+ Mole Percent True Vertical Depth, mSS

Well D Well E Well C Well A DST 1 Well B Well A DST 2

Åsgard, Smørbukk Field

Geologic Layer “A”

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SLIDE 27

3800 4000 4200 4400 4600 4800 5000 5 10 15 20 25 30 35

C7+ Mole Percent True Vertical Depth, mSS

Well D Well E Well C Well A DST 1 Well B Well A DST 2

Åsgard, Smørbukk Field

Geologic Layer “A”

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SLIDE 28

Predicting a Gas-Oil Contact

… “Dangerous” but Necessary

  • Use Isothermal Gradient Model

– Predicts minimum distance to GOC

  • Most Uncertain Prediction using Gas Samples

– 10 – 50 m oil column per bar uncertainty in dewpoint ! – 2 – 10 ft oil column per psi uncertainty in dewpoint !

… Treat dewpoints (and bubblepoints) with special care