SPE 63086 (originally SPE 49269) Miscibility Variation in - - PowerPoint PPT Presentation

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SPE 63086 (originally SPE 49269) Miscibility Variation in - - PowerPoint PPT Presentation

Mar 10, 2023 103 likes •452 views

SPE 63086 (originally SPE 49269) Miscibility Variation in Compositionally Grading Reservoirs Lars Hier, SPE, Statoil Curtis H. Whitson, SPE, NTNU and Pera BACKGROUND Miscible gas injection processes are well documented in the literature.

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SLIDE 1

SPE 63086

(originally SPE 49269)

Miscibility Variation in Compositionally Grading Reservoirs

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

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SLIDE 2

BACKGROUND

Miscible gas injection processes are well documented in the literature. Compositional variation with depth has also been studied the past 20 years. However, almost nothing in the literature is found on the variation of miscibility conditions with depth in reservoirs with compositional gradients.

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PURPOSE

Intuitively, it is difficult to picture the variation of MMP with depth for a reservoir with varying composition and temperature. This study shows that a simple variation does not exist, but that certain features of MMP variation are characteristic for most reservoirs.

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SLIDE 4

Fluid Systems

  • Three reservoir fluid systems, each with significant

compositional grading.

  • Lean and enriched injection gases.
  • Peng-Robinson EOS, typically with 15 components, five

C7+ fractions, and no grouping of intermediates.

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SLIDE 5

Calculating Miscibility Conditions

A Multicell Algorithm Developed by Aaron Zick

  • Defines “true” minimum miscibility conditions

(pressure or enrichment)

  • Identifies the developed-miscibility mechanism

– Condensing/Vaporizing Drive (C/V) – Vaporizing Gas Drive (VGD) – Condensing Gas Drive (CGD) – First Contact Miscible (FCM)

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SLIDE 6

Calculating Miscibility Conditions

  • Zick algorithm is fast and uses an internally-consistent

numerical solution.

  • Zick algorithm has been verified in this study by

numerous 1D numerical (“slimtube”) simulations for a large range of fluid systems, injection gases, and miscible mechanisms.

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SLIDE 7

MMP from Slimtube Simulations

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SLIDE 8

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

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SLIDE 9

MMP versus Depth

Example 1

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MMP versus Depth

Example 1 – Lean Gas Injection

VGD VGD VGD

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MMP versus Depth

Example 1 – Enriched Gas Injection

C/V C/V C/V VGD

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SLIDE 12

MMP versus Depth

Example 1

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MMP versus Depth

Example 1 – Varying Enrichment

C/V

C/V

C/V

C/V VGD

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SLIDE 14

Oil Reservoirs – Summary

MMP always increases with depth, both for VGD and C/V mechanisms.

  • VGD MMP is always greater than or equal to the

bubblepoint pressure.

  • C/V MMP can be greater than or less than the

bubblepoint pressure.

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SLIDE 15

Gas Condensate Reservoirs – Summary

In gas condensate reservoirs, MMP variation with depth follows exactly the dewpoint variation with depth

  • nly

when miscibility develops by a purely VGD mechanism.

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SLIDE 16

Gas Condensate MMP – Summary

For a depleted gas condensate reservoir, the composition of the retrograde condensate controls the C/V MMP.

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SLIDE 17

Gas Condensate MMP – Summary

MMP can be significantly lower than the dewpoint pressure. This requires that the C/V mechanism exists, which usually results from the injection of an enriched gas (or CO2 ?).

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SLIDE 18
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SLIDE 19

C/V Mechanism in Gas Condensates below Dewpoint Pressure

Key features in 1D slimtube simulations:

  • An oil bank develops, increases in size, and propagates

through the system.

  • The miscible front is located on the ‘’back side’’ of the

saturation bank, leaving behind a near-zero oil saturation.

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SLIDE 20

C/V mechanism in a depleted system

(gas condensate reservoir, 0.7 PV injected)

0.0 0.2 0.4 0.6 0.8 1.0 200 300 400 500 600 700 800 900 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Normalized Distance from Inlet Density, kg/m3 Oil Saturation Oil density Gas density Oil saturation
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Oil bank development

(depleted gas condensate reservoir)

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Normalized Distance from Inlet Oil Saturation Slug case: 0.24 PV injected 0.48 PV 0.72 PV 0.96 PV Continuous rich gas: 0.24 PV injected 0.48 PV 0.72 PV 0.96 PV
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CONCLUSION, MMP below Dewpoint Pressure

Dispersion has a strong influence on the development of miscibility by the C/V mechanism for lean gas condensates.

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Elimination of numerical dispersion

(gas condensate reservoir)

0.00 0.02 0.04 0.06 0.08 0.10 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 N -1/2 RF at 1.2 PV injected 100 200 500 1000 Pressure: (bara) 350 330 312 300 290 275 260
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SLIDE 24

Slimtube displacment STO recoveries

(gas condensate reservoir)

250 275 300 325 350 0.5 0.6 0.7 0.8 0.9 1.0 Pressure, bara RF at 1.2 PVinj Extrapolated to infinity 500 grid cells 200 grid cells 100 grid cells
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CONCLUSION, MMP in depleted reservoirs

For a depleted retrograde condensate reservoir, the composition of the retrograde condensate at the start of a cycling project controls the C/V MMP.

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SLIDE 26

CONCLUSION, MMP in depleted reservoirs

Simple 1D slimtube simulations demonstrate that slug injections as small as 10% PV of enriched gas in depleted gas condensate systems can develop miscibility at the same conditions as continuous enriched-gas injection.

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SLIDE 27

Recomendation MMP in depleted reservoirs

For depleted rich gas condensate reservoirs:

  • Perform 3D compositional simulations to evaluate

miscible gas (slug) injection versus traditional dry gas injection.

  • Measure the MMP by traditional slimtube displacement
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SLIDE 28

Key Observation

Miscibility variation with depth due to gravity-induced compositional gradients can be significant. The miscibility variation depends strongly on the mechanism

  • f developed miscibility:
  • Condensing/Vaporizing Mechanism ( C/V )
  • Vaporizing Gas Drive ( VGD )
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SLIDE 29

NOTE

If the condensing/vaporizing mechanism exists, then the true C/V MMP will always be less than the VGD (vaporizing) MMP.

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MMP variation with enrichment

at a specific depth in an oil zone

0.0 0.2 0.4 0.6 0.8 1.0 250 300 350 400 450 500 Enrichment Level, fraction EOS-Calculated MMP, bara Bubble Point Pressure E* VGD MMP C/V MMP
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Vaporizing MMP variation with depth (dry gas injection in SVO reservoir )

200 300 400 500 600
  • 2900
  • 2800
  • 2700
  • 2600
  • 2500
  • 2400
  • 2300
  • 2200
EOS-Calculated MMP, bara Depth, m SSL GOC Reservoir Pressure Saturation Pressure E = 0.0 (dry gas)
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SLIDE 32

MMP versus Depth

Example 2

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Gas Condensate Reservoirs – Summary

  • MMP on the gas side of the GOC is less than or equal

to the MMP on the oil side of the GOC.

  • MMP may decrease slightly at depths above the GOC

until a minimum is reached

  • MMP increases until the condensing part of the

mechanism disappears and the MMP equals the dewpoint (VGD MMP) variation with depth.